Chapter 5 Scintillator detector fabrication

Chapter �

Scintillator detector fabrication

�� Overview

This Chapter describes the MINOS scintillator system� The �rst Section gives an overviewof the baseline design� Section �� sets the performance criteria for the scintillator systemand Section �� describes the interfaces of the scintillator system with other MINOS systems�Together� these �rst three Sections provide a complete overview of the scintillator system�Section �� discusses in detail the elements of the scintillator WBS�� including components�capital equipment costs� assembly procedures and calibration procedures� Finally� Section ��discusses future engineering and optimization of the design�

�� Description of the scintillator system

The MINOS detector uses extruded plastic scintillator which is read out by wavelengthshifting �WLS� �bers coupled to multipixel photodetectors� This technique provides excellent energy and spatial resolutions� The baseline design relies only on existing technology forwhich performance measurements have been made� The major components of the scintillatorsystem are

� Scintillator strips� The active detector planes are composed of extruded polystyrenescintillator strips� � cm thick and �� cm wide� Each detector plane is an octagonalarray of �� parallel strips� Each scintillator strip is coextruded with a TiO� outerlayer for re�ectivity and a groove for a wavelengthshifting �ber� Several existingscintillator formulations and producers can meet MINOS speci�cations�

� Fibers� Wavelengthshifting �WLS� �bers are glued into a groove in each scintillatorstrip� In the far detector the �bers are read out from both ends� while the shorter neardetector �bers are read out from only one end� Fibers with acceptable light outputand attenuation are produced by Bicron and Kuraray� Figure �� shows a sketch of asingle scintillator strip with the �ber readout�

� Scintillator modules� The scintillator strips are assembled into either ��wide or��wide �� cm or �� cm wide� modules for shipment to the near and far detectorsites at Fermilab and Soudan� The shapes of the modules are designed to cover the

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8 m

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Figure �� Sketch of a single scintillator strip� Light produced by the passage of particlesis multiply re�ected inside the strip by an outer re�ective coating� and eventually may beabsorbed inside the WLS �ber� The �ber reemits light isotropically and some of this lightis captured within the �ber and transmitted to the photodetectors�

octagonal steel planes� The strips within a module are glued to a lighttight outeraluminum skin� forming a rigid structure for easy handling and mounting� The endsof the modules have lighttight plastic manifolds which route the WLS �bers to bulkoptical connectors�

� Light guides to photodetectors� Clear �ber ribbon cables carry light from thedetector modules to multiplexing boxes where the photodetectors are mounted� Opticalconnectors are used for all �ber optics connections� The ribbon cables plug into thefront faces of the multiplexing boxes�

� Multiplexing boxes� Each detector plane is divided into eight �logical modules��Each logical module consists of �� adjacent strips �about �� cm in width�� Eight �bers�one from each of eight logical modules� are multiplexed onto a single photodetectorpixel and its associated electronics channel� Demultiplexing is straightforward becausethe local order of �bers on one side of the detector is permuted with respect to theother side� giving unique patterns of light on the two sides� Each box serves twodetector planes for one side� i�e�� a total of three PMTs resides in a box� The �foldmultiplexing is practical because of the limited spatial extent of neutrino events withina single detector plane� Figure �� shows a schematic of the readout chain for thescintillator strips� Figure �� shows a schematic of the multiplexing scheme�

� Photodetectors� The photodetector is the ��channel Hamamatsu R��U��M��photomultiplier� These PMTs are housed in the multiplexer boxes and will coupledirectly to the frontend electronics� Each pixel of the PMT reads � signal �bers fromdi�erent logical modules� A total of �� pixels �� photomultipliers� are required to readout each side of a detector plane� Figure �� shows a schematic of how photodetectorsare placed in the MUX boxes and interface to the electronics boxes� The assembly ismodular and acts as a Faraday cage for the PMTs and electronics�

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� Calibration� Calibration of the scintillator system is performed regularly using acombination of light injection to give the response curve of the photodetectors� andcosmic ray muons to normalize the response curve to energy� This necessitates anextrapolation over two orders of magnitude in light�energy� A calibration module�which can be placed in a test beam of hadrons and electrons� is used to determine thehadronic energy scale and the EM energy response and resolution� Radioactive sourcespermit quick checks on scintillator response�

Table �� gives a summary of the scintillator system components�

Item Each far Each far Full far Near Totalplane supermodule detector detector

Number of scintillator planes � �� Area of scintillator �m� �� Mass of scintillator �kg �� Number of scintillator strips �� Length of scintillator strips �m �� Length of WLS �ber �m �� Number of ��wide modules � �� Number of ��wide modules � �� Number of M�� PMTs � �� Number of M�� PMT pixels �� Number of readout channels �� Number of MUX boxes � �� Number of �fold multiplexed pixels �� Number of notmultiplexed pixels �� Number of �fold multiplexed pixels �� Length of �single� clear �ber �m ��

Table �� Summary of basic quantities of the MINOS detector components� The valuesshown are approximations of exact engineering calculations�

Our choice of twoended readout of the scintillator strips o�ers the following advantages

� Better uniformity in light response from two ends� which may reduce systematic differences between the near and far detectors�

� Higher observed light level than with oneended readout for the same scintillator lightoutput�

� Redundant trigger capabilities� permitting detailed studies of trigger e�ciency acrossthe detector�

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Figure �� The MINOS scintillator system multiplexes eight �bers onto each PMT pixel�The multiplexing scheme combines one �ber from each of eight �logical modules� within asingle scintillator plane� The �bers on a single pixel are separated by approximately onemeter on the face of the detector� The pixel assignments of �bers on opposite sides of theplane are permuted with respect to the other side to permit demultiplexing in software�Because neutrino events are narrower than the � m multiplexing pitch� this approach savesmoney in PMTs and electronics without degrading sensitivity to neutrino physics�

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Figure �� Sketch of the layout of a multiplexer box with phototubes and interface to theelectronics� Both the multiplexer box and electronics are modular and the phototubes canbe removed from the assembly insitu by removing the electronics board�

�� Reasons for selection of solid scintillator

Solid scintillator has been used extensively in many particle physics detectors and in particular has frequently been the active detector of choice for sampling calorimeters� Extrudedscintillator has already been employed in the D� upgrade�� Some of the features whichmake solid scintillator attractive are

� Good energy resolution� We expect the energy resolution for �� cm steel platesto be about ��

pE for EM showers and ��

pE for hadronic showers �E in GeV��

� Excellent hermeticity� There are very small gaps between strips�

� Good transverse segmentation� Analyses of simulated events show little improvement in physics measurement capabilities as strip widths are reduced below � cm� Thebaseline design uses �� cm wide strips�

� Flexibility in readout� With solid scintillator� it is particularly easy to implementtwoended readout which o�ers several advantages as described above�

� Fast timing� Scintillation detectors have the intrinsic property of permitting nanosecond timing� This has advantages for the study of atmospheric neutrinos and permitsa sensitive search for delayed signals in the neutrino beam�

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� Simple and robust construction� Assembly of solid scintillator strips into detectormodules requires little hardware and experience� Techniques for �ber connections havebeen completely worked out and implemented in major systems for both the D� andCDF upgrades�

� Potential for distributed production� Because of the simplicity� the assembly andtesting of complete modules could easily be distributed to multiple sites�

� Long�term stability� Our tests of extruded plastic scintillator show no serious agingor crazing problems� Since the stresses on the plastic are small in our design� crazingis not expected to be a problem in any case�

� Ease of calibration� A complete scheme for performing calibrations using a testbeam module� muons� laser pulses� radioactive sources and charge injection� has beendesigned and is described in this document�

� Low maintenance� We expect the system to be quite robust and to require littlemaintenance�

� Reliability� There are no catastrophic failure modes for solid scintillator which cannotbe externally repaired� A possible longterm decrease in light output can be correctedusing calibration data� Because there is little to go wrong� the detector is likely toachieve its intrinsic measurement capabilities�

�� Scintillator light output� transmission and detection test

In order to demonstrate the feasibility of the scintillator system we have constructed prototypes and measured their light output and uniformity using cosmic rays� All of the components related to the production� transmission and detection of light� which are described inthis Chapter� were tested in the following prototype assembly� The setup consisted of twoprototype scintillator modules� each with �� strips� Other features included

� � m long scintillator strips �� cm � �� cm wide� coextruded with a re�ective coatingand with a WLS �ber groove�� See Section �� for a more detailed description�

� �� mm diameter Kuraray wavelengthshifting �bers�� were glued in the grooves usingan the baseline optical epoxy �Epon resin and TETA hardener��

� End manifolds which route the appropriate lengths of WLS �bers from the strips tobulk optical �ber connectors�

� To simulate a real detector situation the wavelength shifting �bers were extended by� m by adding a �� mm diameter clear�ber ribbon cable running to a box housingthe photodetectors� A connector was used on each end of the clear �ber cable�

� The light was routed to the photodetectors through an additional �� cm of clear �berinside the photodetector box�

� The photodetectors were ��pixel Hamamatsu R��U��M�� PMTs�

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� The prototype module readout was triggered on cosmic rays by a system of externalscintillation counters placed in several locations along the strips�

Figure �� shows the mean e�ective light yield at each end and for the sum of thesignals from both ends� expressed in terms of the number of photoelectrons registered bythe Hamamatsu photomultipliers� The events for which the photoelectron yield is plottedwere selected to be isolated minimum ionizing cosmic rays� The di�erence in the light levelson the two sides is due to di�erent WLS �ber lengths extending beyond the ends of thescintillator strips on the two ends of the module� �The end with the longer WLS extensionsgives lower light�� We observe that

� The sum from both ends gives an average of more than �� photoelectrons at all pointsalong the scintillator strip�

� The light yield of the sum has a weak dependence on the distance from the end of thestrip �i�e�� the distance to a photodetector��

As described in Section �� the observed light yield is adequate for MINOS� Speci�cally�the light yield is more than twice the minimum amount necessary for physics measurements�as determined by Monte Carlo simulations� This provides contingency for possible variationin� or degradation of� light output which might occur in the construction and operation ofthe experiment during its lifetime�

�� Calibration systems

Calibration of the hadronic energy response is of great importance in MINOS� In order toensure a wellunderstood calibration at the required level of precision and accuracy� we willemploy a combination of several calibration techniques

� A testbeam calorimeter module for setting the overall energy scale and resolution�

� A combination of a light injection system and cosmicray muons for calibration ofshortterm and longterm variations�

� Radioactive sources for troubleshooting and to cross check other calibration methods�

Measurement of the total hadronic energy of events in MINOS is crucial to a completeset of neutrino oscillation measurements� The ability to measure �m� precisely depends onthe absolute calibration of the hadronic energy measurement� In order to reduce systematiclimitations� we plan to calibrate the near and far detector hadronic energy responses to about�� relative and �� absolute uncertainty� Since it is impossible to illuminate the near and fardetectors insitu with highenergy hadron test beams� we must make careful use of severalcalibration tools to achieve this goal�

The fundamental calibration of the hadronic energy scale is achieved using a specialcalibration module for a series of testbeam and other calibration runs� Data are acquired ina test beam for muons� electrons and hadrons� Data from cosmicray muons� a radioactivesource and lightinjection are also collected during the testbeam running to help translatethe calibration to the near and far detectors�

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Figure �� Results of photon yield measurements for single cosmic ray muons from a fullscale prototype using �� mm diameter �bers� The light measured at each end and the sumof the two ends is shown as a function of position along the strips� The di�erence in thelight from the two ends is due to di�erent lengths of WLS �ber extending beyond the endsof the scintillator strips�

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Cosmicray muons provide the best means of calibration of the far detector and perhapsthe best means of calibration for the near detector as well �although muons from upstreamneutrino interactions may play as important a role there�� The calibration is obtained bycomparing muon energy deposition at di�erent points in the detector with muon energydeposition in the testbeam module and hence with the hadronic energy data from the testbeam� Due to di�erences in muon energies at the di�erent depths of the detector sites� thecalibration module could eventually be deployed at each detector site for a direct comparisonof cosmicray muon data� This would ensure that there is no systematic error in translationof the testbeam calibration� The need to check for systematics of this type will depend onthe outcome of neutrino oscillation measurements�

It is important to be able to track shortterm variations in the response of the system�Light is injected into the WLS �bers to measure the response of the photodetectors andelectronics through the full dynamic range of the system� This is one of the two mainfunctions of the light injection system� The second function is to identify any connector or�ber problems� In addition to the light injection system� the electronics is calibrated bydirect charge injection �see Chapter ��

Muons provide the energy normalization for the light injection system� Because it requiresabout a month of muon data per strip at the far site �much less time is needed at the near site�to provide an absolute calibration� the light injection system is used to keep the photodetectorgains approximately constant during the time over which the muons are recorded�

The responses of all scintillator modules are mapped in detail using a radioactive sourceduring module construction� In addition� a tube which can hold a radioactive source isinstalled at each end of every scintillator module to permit insertion of a wire source� afterthe detector plane has been installed� for shortterm cross checks on other calibrations anddebugging at installation time�

�� Description of the scintillator factories

Construction of the components for the scintillator system requires a few di�erent typesof �factory� operations� Most of these operations are quite compatible with resources andskills available in collaborating laboratories and universities while some require industrialproduction� Many of the basic components of the system are already available as �catalog�items� Examples include the photodetectors� WLS �ber and clear optical �ber�

Some of the other components require specialized industrial production based on speci�crequirements for MINOS� Examples of these items include the scintillator strips� the endmanifold and coil bypass components of the scintillator modules� and bulk optical connectors�We have carried out an extensive development program for extruded scintillator over the lastyear in order to develop an industrial product which meets our light output demands foran acceptable cost� At present� we have a production technique which involves a cooperative e�ort between MINOS and an industrial extrusion house� Quick Plastics�� Since thisindustry is not experienced in the production of scintillator and the subtleties of measurement of light output� we envision a continued cooperative e�ort for production of scintillatorfor MINOS� In addition� two commercial producers of plastic scintillator �Kuraray�� andPolycast�� have been actively pursuing production of extruded scintillator� Kuraray hasdelivered scintillator of good quality and continues their development program� We are in

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close contact with both of these companies to ensure that their products will meet the speci�cations of the scintillator for MINOS� Because these products are not yet �nalized� weassume here that the production will be via a direct cooperative e�ort of our own technicalsta� with industrial plastic extruders� However� we expect that Kuraray and Polycast willbe able to provide comparable products and we will evaluate bids for production when weare ready to place orders�

The three main systems which must be fabricated �in house� by MINOS are the scintillator modules� assembled clear�ber ribbon cables �with connectors attached and polished�and multiplexing boxes which house the photodetectors and route light from signal �bersto the appropriate pixels on the photodetectors� The assembly of the scintillator modulesrequires the most manpower and equipment�

The scintillator modules could be produced at a single production site running two shiftsper day� However� we expect that the optimal production scenario will include two factory locations for module production� This permits faster production �or contingency in theschedule� and more e�cient use of collaboration resources while keeping costs low� Attractive features of the assembly of plastic scintillator modules are that the cost of specializedassembly equipment is relatively low� the space required for assembly is not particularly largeand the level of skill required in the assembly is relatively low� The necessary space� skillsand oversight capabilities exist at several collaborating laboratories and universities�

The production of scintillator modules involves the following major steps

�� Gluing WLS �bers into scintillator grooves�

�� Assembly of strips into ��wide and ��wide modules�

�� Routing of �bers through the end manifolds and into the bulk optical connectors�

�� Potting and polishing of optical connectors�

�� Closing the completed assemblies and checking for light leaks�

�� Mapping of modules using radioactive sources�

Specialized machinery and �xtures have been designed to facilitate this work�The production of optical �ber ribbon cables and boxes to house photodetectors require

relatively simple equipment� readily available in most laboratory and university shops� Theonly specialized equipment needed are assembly jigs and �y cutters for polishing of opticalconnector faces�

We plan to begin routine production of scintillator components for MINOS detectors inOctober �� The �rst commercial orders for various components would precede this byseveral months�

�� Requirements and performance criteria

The technical requirements on the scintillator system have been set from a combination ofphysics studies� general considerations about detector response and practical considerations�They are

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�� Light output� The light output must be su�cient so that the hadronic energy resolution is better than ��

pE and that the e�ciency for observation of a muon crossing

a strip is greater than �� This is expected to be the case as long as the total numberof observed photoelectrons per minimumionizing particle crossing a scintillator layeris greater than �� with discrimination at the single photoelectron level� A factor ofabout � times more light than this �� is desirable to account for assembly variationand aging of components� The current baseline design meets this requirement� To theextent that higher light output will help with other technical considerations �e�g�� noiselevels�� higher light output will be pursued as long as the overall cost of the detectoris not signi�cantly impacted�

�� Uniformity� In order to ensure that it is possible to correct for position dependenceof showering events� the light output of the scintillator strips should vary by no morethan �� with respect to a nominal response at that location �after correcting forattenuation in the WLS �ber��

�� Attenuation� The light observed from the near and far side of a strip �by the detectorat the near end� should di�er by no more than a factor of ��

�� Timing� The time resolution from the sum of strips within a scintillator plane shouldbe less than � ns for �� pe�s and � ns for � pe�s�

�� Stability� The light output of the scintillator system should have longterm stabilitywith an expected decaytime of at least �� years� Shortterm variations must be measurable so as to permit relative energy calibration for hadronic showers between thenear and far detectors at the level of ��

�� Calibration� The hadronic energy response should be able to be calibrated to arelative error between the near and far detector of no more than �� up to at least�� GeV� An absolute calibration of �� will be made using a test beam measurement�

�� Linearity� The detector response to hadronic showers should be linear to within ��between � GeV and �� GeV�

�� Crosstalk� The crosstalk between scintillator channels should be less than ��

�� Transverse pitch� The scintillator strips should be � cm in width for pattern recognition on EM showers�

�� Modular construction� The scintillator strips must be assembled into modules whichare easy to handle� relatively rugged and provide lighttight seals�

�� Cost� The cost should be as low as possible given the above considerations� Theoverall cost of the scintillator system should be reviewed with respect to other detectorcosts prior to �nal production in order to produce a best overall optimization of physicscapability�

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�� Interfaces to other MINOS systems

Interfaces between the scintillator system and the other MINOS systems have been de�nedas follows

� The scintillator fabrication task provides the scintillator modules� clear optical cables�multiplexer boxes� phototubes� HV bases and the various calibration hardware�

� Scintillator modules mount to the steel using mounting bars at the ends and strapsattached to plates welded to the steel at intermediate points� The scintillator modulesare designed to be mounted on the steel prior to lifting the steel plane into place�

� The interfaces between the scintillator system and electronics system are the mechanical and electrical connectors between the multiplex boxes and the electronics modules�High voltage for the phototubes is provided from these modules by the electronics task�

� Packing and shipping of scintillator modules is part of the scintillator system production responsibility� Handling of the modules at the near and far detector sites is theresponsibility of the installation tasks�

� All test and calibration equipment for the scintillator system �including their use duringinstallation� is the responsibility of the scintillator task�

� The cavern out�tting task provides the rack platforms� located along the �� faces ofthe octagons� for mounting the scintillator multiplexing �MUX� boxes and electronicsracks and modules� The scintillator task is responsible for production and testingof the MUX boxes and the clear �ber cables between the modules and MUX boxes�Installation and insitu testing of the MUX boxes and cables is the responsibility ofthe installation tasks�

� The general experiment database system provided by the electronics task is used tomanage various construction and calibration information� Data from assembly andtesting of scintillator modules are stored in this database for use during installationand analysis� Scintillator modules are marked with bar codes for reading at installationtime� The barcode reader and associated software are supplied by the scintillator task�

�� Description of WBS elements

�� Scintillator strips �WBS ��

The recent development of extruded scintillator which can be inexpensively mass producedin very long strips is one of the reasons that solid scintillator can be used in MINOS� Theproduction of extruded scintillator for MINOS has built upon work done by Fermilab inconjunction with the D� upgrade��

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Figure �� Sketch of a scintillator strip with groove and re�ective coating�

�� Description of scintillator strips

The scintillator strips are made of polystyrene� infused with the �uors PPO �� and POPOP�� This compound is melted and extruded in the shape of a rectangular bar with anarrow groove along the center of one of the wide sides� as shown in Figure �� The grooveis �� mm deep� su�cient to contain a �� mm diameter wavelengthshifting �ber� A thin�� mm thick� re�ective jacket� composed of TiO� infused in polystyrene� surrounds theentire scintillator bar except for a small region near the groove� Each scintillator strip is�� cm wide� �� cm thick� and up to � m long� as shown in Figure ��

Traditionally� the manufacturing of scintillator strips has been accomplished in two steps��rst mixing �uors into polystyrene� extruding that mixture and letting it cool and then ina later step remelting the scintillator mixture to extrude strips of a speci�ed shape� Inthe last year� we have developed a onestep process where the �uors are infused with rawpolystyrene pellets in the same machine which is used to extrude �nal scintillator strips� Intest production� this technique has proven to be reliable and cost e�ective and we have nowspeci�ed it as the baseline� We consider the twostep process to be a contingency option incase scaling up the onestep process proves too di�cult�

In the onestep or �inline� production process� �uors are �rst tumbled with dry polystyrene pellets which have been held under an argon atmosphere for several days prior toextrusion� The PPO and POPOP are premeasured into convenient packages for addition toa set amount of polystyrene pellets during the mixing process� The mixture of pellets and�uors are fed into an extrusion machine which melts the polystyrene� allowing the �uors to

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Figure �� Detailed crosssection of a scintillator strip�

di�use uniformly� The scintillator mixture is extruded through a die to produce the desiredstrip cross section� As the scintillator is extruded through the die� the outer re�ective coatingof polystyrene mixed with TiO� �� by weight� is added through material injected from asecond� �satellite� extrusion machine which mixes the polystyrene and TiO�� As the plasticemerges from the die� it is further formed using vacuum sizing and cooled with air andwater� The scintillator is extruded continuously and strips are rough cut to lengths of ��and �� m�

The total weight of plastic scintillator to be installed in the near and far detectors isapproximately �� pounds� We estimate that it will require �� pounds of rawpolystyrene to produce all of the scintillator strips because of ine�ciencies in the extrudingand cutting processes� About �� of the scintillator strips on the far detector are � m long�The remainder are between � m and �� m long� as the octagonal shape of the detectordictates� By cutting a single �� m long strip into two sections� it is possible to keep theamount of waste material small and still have each strip of exactly the right length for itsoctagon location� The length of near detector strips ranges from �� m to �� m� Scintillatorstrips are rough cut at the extruding facility and are cut to the exact lengths required at themodule assembly factories�

The commercial production of this quantity of scintillator strips is within the capacityof typical commercial extruders over a � year time span� Faster production could be accomplished by having additional extrusion machines operating in parallel� However for ourexpected needs a single machine is su�cient� We currently have contracts with two extruding

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companies� Quick Plastics�� and Royalite Thermoplastics�� to produce prototype scintillator strips for MINOS� Kuraray has also expressed interest in the scintillator production forMINOS as has Vladimir Technoplast in Russia�

�� Performance measurements

It is important to understand the light production� collection and uniformity properties ofextruded plastic scintillator� These properties will vary with factors such as the shape of thestrip� re�ective coating and clarity of the material� We must also determine the uniformitywhich can be achieved during actual mass production of extruded strips�

The TiO�loaded coextruded layer on the strips requires less manpower than wrappingstrips with a re�ective material such as Tyvek� We have extruded the strips both with andwithout the TiO� coating to measure the re�ection e�ciency of the coating compared toTyvek� We found no observable di�erence in the amount of light collected with the TiO�

compared to Tyvek� making the coextrusion an attractive and coste�ective re�ector�We have compared the collection of light from a WLS �ber laid in an extruded groove on

the broad side of a scintillator strip with that from a �ber placed in an extruded hole in thecenter of a scintillator strip� A dry �unglued� �ber in the groove yields about �� less lightthan a dry �ber in the hole� However� for our geometry and scintillator material� we �ndthat a �ber glued in the groove yields �� times more light than a dry �ber� Since gluing ismuch easier in a groove than a hole� we have chosen to glue �bers in grooves for our baselinedesign�

Our studies of the aspect ratio of scintillator strips �width and thickness� have shownthat� for �cm thick extrusions� a �cm wide strip gives about �� times more light than a�cm wide strip� Simulations of neutrino events show that changing from �cm to �cm stripshas very little e�ect on physics capabilities� The lower light yield of �cm strips still meetsMINOS requirements� and the cost is lower than for narrower strips� We have thereforechosen �cm wide strips for the baseline design� The optimal aspect ratio may be sensitiveto the re�ectivity of the outer surface and to the clarity of the polystyrene to scintillationlight� we are continuing our studies of these e�ects�

For the baseline scintillator strips� we have measured a number of strips for uniformityin the light output� both along the strip lengths and transverse to their long axes�

�� Longitudinal uniformity

We have studied the uniformity of the light output of several scintillator strips bymeasuring photomultiplier tube current while moving a beta source along the strips�The measured light output at each location has been corrected for the �ber attenuation�The results are shown in Figure �� for strips which were intentionally taken fromdi�erent times of an extrusion production run� The variation in the light collectione�ciency of the WLS �ber at di�erent locations is negligible� Hence� the �� spreadin the measurements is probably due to the nonuniformity of the scintillator strips andthe variation in optical coupling between �bers and strips�

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Figure �� Scintillator longitudinal uniformity Responses of the scintillator strips �arbitrarynormalization�� corrected for �ber attenuation� are plotted versus the position in �a�� andthe projection is histogrammed in �b��

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Figure �� Scintillator transverse uniformity�

�� Transverse uniformity

We have measured the uniformity of the light output of scintillator strips transverseto their lengths using cosmicray muons� The muon trigger consisted of two narrowscintillators above and below the scintillator strips� Measurements of two strips areshown in Fig� �� The light output decreases by about �� near the edge� mostly dueto the fact that the thickness of the scintillator in these extrusions was slightly smallernear the edge� This was the result of an early production process� all of our commercialextruders have assured us that �nal scintillator strips will have no such variation� Weexpect our �nal strips to have thickness uniformity to better than about ��

�� Fibers �WBS ��

�� WLS �bers

The wavelengthshifting �WLS� �bers which shift the blue scintillation light to green area critical component in the overall light collection scheme� Blue photons produced in thescintillation process make many re�ections from the highly re�ective outer layer of the coextrusion� The blue photons eventually hit a �ber where they are absorbed by the WLS Y��uor and reemitted as green photons� The absorption spectrum of the Y�� uor� centeredat a wavelength of �� nm �blue�� has only a very slight overlap with the emission spectrum�centered in the green beyond �� nm� so that selfabsorption in the �ber is small� The �bersthen act as light guides to channel the green light� through optical connectors and lengthsof clear �bers� to the photodetectors� This provides a very e�cient means of �focusing� thelight into a smallarea photodetector� whose cost is roughly proportional to photocathode

��

area� This is one of the main features which makes scintillator readout practical for MINOS�Measurements and Monte Carlo calculations have been used to study the various factors

a�ecting light collection i�e�� re�ectivity of the outer coextrusion� and scintillator��ber sizesand geometry� We have chosen to use �� mm diameter �bers which maximize the use ofthe available area of photocathode on the PMT and give the required light output with ourextruded scintillator strips� The total length of WLS �ber required �including allowance forspares and waste� is about �� km� The �bers are doubleclad to give a maximum trappingfraction for the green light the inner core containing the WLS �uors is polystyrene �refractiveindex n� � �� a thin intermediate layer is acrylic �n� � �� and the thin outer claddingis a poly�uor �n� � �� For green light produced on the axis of a �ber� the fraction oflight trapped and traveling in one direction is given by �n� � n��n�� This factor is ��Both experiment and photonbookkeeping have veri�ed that this simple treatment is correct��Light produced o�axis has a greater trapping fraction� but these rays are attenuated morerapidly��

One of the most crucial properties of the WLS �ber for determining the light yield at thephotodetector is its e�ective attenuation length when the source of green light is remote fromthe photodetector� MINOS requires a very large number of �bers with lengths in excess of� m� signi�cantly longer than the requirements of any previous experiment� We have mademeasurements of many �bers from the two vendors� Bicron�� in the U�S� and Kuraray�� inJapan� Performances of some batches of WLS �bers are shown in Figure �� All of the�bers measured from the batches represented here are acceptable for use in MINOS� Theresults shown here come from three di�erent batches of �ber� two from Bicron and one fromKuraray� The Bicron �bers are all � mm diameter BCF��A while the Kuraray �bers areall � mm diameter� doubleclad� nonStype �bers with �� ppm Y�� uor� �Although notshown� we have measured that �� mm diameter �bers have the same attenuation length as�� mm diameter�� The batches of Bicron �bers represent production of about �� m of�ber while the Kuraray �ber was from a �� m sample� Further orders have been placedto study possible variation in larger production batches� The better batch of Bicron �berrepresents a newer production of that �ber� We conclude that either of these manufacturerscan supply �ber of high quality for MINOS� The Kuraray �bers are somewhat sti�er thanthe Bicron �bers and require somewhat more space in the endmanifold design�

Aside from the di�erences in the absolute light output in di�erent batches� all WLS �bersshow similar characteristics� The attenuation is approximated quite well by a sum of twoexponentials one with a short attenuation length of less than � m and one with a much longerattenuation length of � to � m� the crucial component for MINOS� The short component isdue to selfabsorption of the green light in the WLS �ber and the short attenuation lengthagrees reasonably well with emission and absorption data provided by the manufacturers�

We have found that di�erent batches made months apart can have signi�cantly di�erentvalues for the longer attenuation lengths� The best long attenuation length that we havemeasured is �� m� in �bers from Bicron� This appears to be the best ever producedby that company� and also appears to be the longest attenuation length reported in theliterature� It seems likely that this is the best that can be achieved and may represent thelimit set by the properties of the polystyrene core of the �bers� The attenuation length ofMINOS WLS �bers must be at least �� m�

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Figure �� Light collection and attenuation in WLS �bers� The current from a phototube ismeasured as a scintillator is placed at various positions along the length of the �ber� Bicron �and Bicron � are two batches produced in the summer and fall of �� respectively� TheKuraray batch was produced in December of �� All results shown here are acceptable forMINOS� See text for additional details�

�� Clear �bers

Clear�ber ribbon cables are used to transmit light from the WLS �bers to the multiplexingboxes� We plan a similar approach as used for construction of these ribbon cables for theCDF endplug upgrade�� MINOS ribbon cables consist of eight or ten clear �bers enclosedin an outer black plastic coating which provides protection and light tightness� Mitsubishio�ers a cable of this type and has provided a quotation for production for MINOS purposes�The �bers are �� mm diameter� doubleclad polystyrene� manufactured by Kuraray� and arespaced �� mm apart� When coupled to WLS �bers� the clear �ber cables act as extensionsof the WLS �bers� but with better attenuation length� �Hence� more light is observed thanif a similar length of WLS �ber were used�� The attenuation length of clear�ber cables hasbeen measured to be �� m for light which is already collimated �as it is coming from a fewmeters along a WLS �ber��

The clear �bers are routed along the edges of the steel detector planes� from the scintillator modules to the MUX boxes� The routing for the far detector is shown in Figure ��This routing minimizes the length of clear �ber required while keeping readout isolated be

��

tween scintillator planes� The total length of clear �ber required for construction of theribbon cables for both the near and far detectors is about �� km� slightly more than thetotal length of WLS �ber�

MUX box

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Figure �� Clear �ber routing and scintillator module layout for readout of one view ofscintillator modules for the far detector� Each octagon has eight modules with bulk opticalconnectors at each end�

�� Scintillator modules �WBS ��

�� Design features and requirements

The baseline design simultaneously optimizes several di�erent concerns

� Gaps between individual strips are kept as small as practical�

� The scintillator fully covers the steel in order to keep the �ducial mass as large aspossible�

� Scintillator modules are designed to be lighttight and permit rapid testing�

� Light�ber connections to the scintillator modules use reliable bulk connectors�

� The mechanical design of the modules gives good light output and longterm stability�

� Assembly work at the near and far detector sites is kept to a minimum in order topermit rapid installation� A modular design of preassembled and pretested strips isideal for this purpose�

��

� Total costs for production of scintillator modules are minimized by balancing capitalequipment� component� manpower and shipping costs and use of existing resources�

� Assembly operations and equipment are simple� and permit production and testing ofmodules in both national laboratory and university facilities� sta�ed by local physicists�students and technicians�

All of these features have been achieved in the design described here� The modulesare either �� or �� strips wide glued to a thin aluminum skin which provides mechanicalstrength� lighttightness and �re protection for the polystyrene scintillator� Wavelengthshifting �bers are routed to ��wide bulk connectors at each end of the module through asimple manifold which curves the �bers through a natural bend radius� protects them fromharm and provides a lighttight enclosure� The components have been designed to be ruggedand permit easy assembly and handling of the modules� The thin aluminum skin permitsmapping of the scintillator modules with radioactive sources to test for any problems in theassembly� Fibers are glued into the scintillator strips to maximize light output� The modulesare mounted onto the steel plates using a simple steelstrap technique which permits verynarrow gaps between neighboring modules and a minimal gap between steel plates�

�� Overview of module construction

This Section provides an overview of the hardware architecture of a plane of scintillatorstrips in the far detector� The packaging of scintillator strips into light sealed modules isdescribed �rst� End manifolds� which route WLS �bers to optical connectors at the end ofeach module� are discussed next� Hardware used to attach the modules to the steel absorberplanes is then described�

Each plane contains a total of �� scintillator strips� All of these strips have an identical�� cm by � cm nominal cross section� as described in Section �� However� the lengthsvary from �� m to � m to match the octagonal shapes of the near and far detector absorberplanes�

The scintillator strips are grouped into modules of �� or �� strips strips each� yieldinga total of � modules per plane� The number of strips has been set to permit four ��widemodules in the center of each octagon and two ��wide modules on each outer side of theoctagon� The layout of the modules on a plane is illustrated in Figure �� The modulesare enclosed in aluminum cases to provide a lighttight seal�

A total of four separate module geometries are required for one plane� Two styles ofmodules have ends angled at �� to their length� The next module style has perpendicularends� all strips in this style are � m in length� The last style also has perpendicular ends�but requires a bypass at its center to provide clearance for the magnet coil� The same partsare used for the di�erent styles to minimize the number of unique parts required and tomaximize assembly e�ciency� For example� the two styles having �� ends di�er only inlength� both lengths use the same end manifold components�

The parts comprising a module can be subdivided into three functional groups� The�rst is the scintillator strips themselves� By the time of assembly into a module� the WLS�bers and re�ective extrusion groove cover have been glued to the strips� as described inSection �� Second� a twopiece light seal and structural box is included about the entire

��

periphery of a module� as described in Section �� Third� an end manifold assemblyroutes and protects the WLS �bers extending from the ends of the scintillator strips� thecomponents in the manifolds are described in Section ��

The innermost two modules have a fourth functional component the bypass assemblyto accommodate the magnet coil� The bypass is described in Section ��

The scintillator modules are fastened and supported on the steel plane using severaltechniques� as described in detail in Section �� Eight meter long modules are fastenedto the absorber planes at the end manifolds and at four equallyspaced points along theirlength� �Some of the shorter modules do not require all four intermediate mounts�� Furthersupport is provided by a shelf positioned at the bottom �� edge of an absorber plane �shownas the bottom right �� edge in Figure �� The hardware used to tie the modules to theplanes is described in Section ��

�� Coupling of �bers to scintillator

In prototype tests with extruded scintillator strips� we have found that a signi�cant improvement in light collection is achieved when �bers are glued into the scintillator strip ratherthan just being placed into a dry groove or hole� For the baseline strips and �bers� we�nd a consistent factor of �� more light observed at the photodetector for �bers glued intothe grooves compared to �bers placed into grooves dry� This is independent of the positionalong the strip��ber assembly� Hence� we have decided that in MINOS� �bers will be gluedinto grooves� It should be noted that in some previous applications of WLS �ber readoutof scintillators �tile calorimeters for instance� no signi�cant di�erence has been observed inthe light output when �bers were glued� This is the result of di�erences in materials andgeometry between those detectors and the extruded strips for MINOS�

We have tested several glues which meet MINOS requirements� We have chosen a verycost e�ective glue which has properties very similar to those of Bicron �� epoxy �which hasbeen used extensively in other detectors� but at about �� the cost� The baseline glue isShell Epon ��C resin�� with triethylenetetramine �TETA� hardener mixed at �� parts to�� parts by weight�� We have performed assembly and aging tests using this glue and havecon�dence that it will meet our needs� One concern with use of glue is possible aging andyellowing� Previous aging measurements on BC�� glue over a � year period have shown itto be quite resistant to yellowing� and it does not attack WLS or clear �bers�� We haveperformed our own accelerated aging tests using Bicron �� and the baseline glue and foundthem to have very similar performance �with the baseline being slightly better��

�� Optical properties The index of refraction of the Shell Epon glue is very close to thatof polystyrene� This good match ensures minimal loss of light at the scintillatorglueinterface� helping to give the factor of �� in increased light collection� The light transmission in the wavelength region of interest is measured and is shown in Figure ��Assuming very conservatively that the light from the scintillator traverses an e�ectivethickness of �� m of the glue before reaching the �ber� �� or less of the light willbe absorbed by the glue�

�� Mechanical properties We have glued several tens of �bers into scintillator strips andhave observed no signs of the glue failing to create a good optical bond in normal

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Figure �� Transmission spectrum of �� m thick Shell Epon ��C optical cement �withTETA hardener�� As a reference� the range of light spectrum emitted by the scintillator andabsorbed by the WLS �ber is indicated�

handling� Furthermore� we have subjected some strips to severe mechanical handlingand bending with no observed reduction in light collection� We have also subjectedsome glued strips to repeated severe temperature cycling with no suggestion of the gluereleasing from the scintillator�

�� Re�ective extrusion groove cover We have found that aluminized Mylar works verywell as a re�ective cover above the groove� It can be applied as the �ber is glued inand improves the light collection by about a factor of �� compared with no re�ectivecover�

�� Light case

Each module is enclosed in a sheet aluminum light case to shield the scintillator from externallight and to protect the �ammable polystyrene strips from ignition sources� The architectureof the light cases is described here� fabrication and assembly information is provided inSection ��

The light case is fabricated from ��mm thick ��H�� aluminum sheet� provided bythe manufacturer on a coil� The coil stock is �attened and rolled into shallow Ushapedchannel sections �where the bottom of the U is the module width� at each module factory�Two U channels are used to fabricate one case� with the top being slightly narrower than thebottom� The bottom U channel is positioned on the module assembly table and �lled with�� or �� scintillator strips� The top U channel is positioned over the scintillator strips andnested in the bottom U channel� Figure �� shows a short section of the top and bottom

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caselight

toplightcase

bottom

Figure �� Light case assembly� as the top light case is lowered into place onto the bottomlight case and strip array� prior to crimping the light case edges�

light cases with scintillator strips in place prior to crimping� The sides of the bottom Uchannel are bent down �� to crimp them against the shorter sides of the top U channel�The sides of both the bottom and top U channels are then folded �at against the top of themodule�

�� End manifold

The architecture of the end manifolds for perpendicularended scintillator modules is described in this Section� These manifolds are functionally identical to those for �� endedmodules� The perpendicularended modules have the tightest constraints on �ber bend radius in order to keep the protrusion from the edges of the detector as small as possible� The�snout� design which has been adopted permits all �bers to be routed to one connector whilekeeping the protrusion from the detector edge as small as possible�

The manifold components of a ��wide� perpendicularended scintillator module are illustrated in Figure �� Optical connectors are mounted on posts on the manifold to jointhe WLS �bers to the clear�ber ribbon cables outside the module�

Figure �� shows the detailed design of the end of a ��wide� perpendicularended module� This �gure includes the light injection manifold compartment of the optical �ber connector �Section �� used for strip calibration� Also shown is the mechanical structure�the �integral module mounting bar�� which gives rigidity to the manifold and provides ameans of attaching the module to brackets on the steel octagon� The bend radii of the WLS�bers are controlled by slots in the base section of the manifold� which guide the �bers intothe required paths� The �bers are precut to speci�c lengths and placed in the slots to produce bend radii of �� cm� which is the minimum recommended for �� mm diameter Kuraray�bers� All of the end manifold parts are injection molded from optically opaque PVC�

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variable width seal cover

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variablewidthseal

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Figure �� Sketches of a ��wide perpendicularended manifold with a righthanded opticalconnector outlet� The upper drawing shows the assembled manifold and the lower drawingis an exploded view�

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baseWLS fiber #20

bottom light caseintegral module mounting bar

optical connector

lightinjectionmanifoldcompartment

Figure �� Sketch of one end of a partially assembled ��wide� perpendicularended scintillator module� showing the �ber routing and the module mounting bar�

�� Light injection manifold

Light injection manifolds are included in the end manifold assemblies of each module to allowthe injection of test pulses of light into groups of WLS �bers� The light injection must besegmented so that only a single �ber will be pulsed on any given PMT pixel at one time �butmany pixels can be pulsed simultaneously�� This is accomplished by distributing light eitherto two groups of �� bers each for modules which are �� strips wide� or to three groups of�� and � �bers each for modules which are �� strips wide� The light injection manifoldis an injectionmolded block of polystyrene scintillator with �� parallel grooves on one faceand a single hole that enters halfway into the block a few millimeters above the oppositeface� Each scintillator module will contain either � or � of these light injection manifoldsdepending on the number of scintillator strips contained in the module� Fibers from the lasercalibration source are inserted into the holes in each scintillator block� which stop halfwayinto the block� to illuminate the WLS �bers� The WLS �bers are mounted in the opticalconnector before they are slipped into the grooves of the light injection manifold� The clear�bers from the laser source distribution system enter each scintillator manifold through aseparate optical connector located directly below the optical connector�

�� Module source calibration tube

The source calibration tube assemblies allow small radioactive sources� mounted on pianowire holders� to be moved across the scintillator strips of a module� The tubes are madefrom �mm diameter stainless steel hypodermic tubing and are attached to the aluminumlight cases at each end of a module� The tubes are oriented parallel to the strips near the end

��

manifolds and are curved so that they cross all strips� Each tube is protected by a shield two pieces of steel wire bent to conform to its shape� The tube and shield are glued to theoutside of the light case� The light case is also glued to the scintillator strips in the areaunderneath the tube to ensure that the tube�s position relative to the strips does not change�

�� Coil bypass

A ��cm wide square hole is provided at the center of each active plane to accommodate themagnet coil� For far detector planes the hole is centered between two perpendicularendedmodules� a semicircular area is removed from each of these modules� The semicircular cutextends into the light case and the �ve scintillator strips at the edge of a module� The WLS�bers for the �ve cut strips are made long enough so they can be routed around the coilhole�

The semicircular holes in the a�ected modules are closed with injection molded plasticbypasses� sealed to the light cases with black adhesive� A bypass is illustrated in Fig� ��The bypass provides a lighttight seal� protects the WLS �bers� maintains the WLS �berbend radius at more than �� cm and improves the mechanical integrity of the module in theregion of the hole�

Figure �� Coil bypass�

�� Module mounting hardware

This Section describes the three methods used to attach scintillator modules to the steeldetector planes� The actual installation of this hardware is described in Section ��

The �rst means of attaching modules to steel detector planes is through the modulemounting bars in the end manifolds� Each module mounting bar has a set of holes whichpenetrate the module and the aluminum light case� as shown in Fig� �� Self tappingscrews in these holes are used to attach the both ends of each module to strips of �� gaugesheet steel which are welded to the edges of the steel detector planes� An elastomeric isolatoraround the screws cushions the interface between the steel and the modules�

The second means of attachment uses standard �� mm � �� mm steel packing strapswhich wrap around the modules and thread through �switchplate� brackets tack weldedto the steel plane� These straps prevent the modules from pulling away from the center

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of the absorber planes� Wrapping the straps around two modules at a time minimizes theintermodule gaps�

The third means of attachment is a shelf along the lower �� edge of each plane mountedon the detector� This shelf supports the lower edge of the bottom module� and the weightof the modules in the plane above it� The shelf ensures that the active planes do not sag inthe middle� it does not block access to the optical connectors�

�� Di�erences in near detector modules

The scintillator modules in the near detector share all of the essential features of the fardetector� However di�erences in the size and functional regions of the near detector resultin some di�erences in module construction and layout

� The modules for the fully instrumented planes� e�g�� in the muonspectrometer section�are similar to those of the far detector except that they are at most � m in length andare read out from only one end� Modules in the muon spectrometer section have �foldmultiplexing to the photodetectors instead of the �fold multiplexing used for the fardetector�

� The modules in the partially instrumented planes of the target�calorimeter sectionsare less than �� m long and are also read out from only one end� None of the modulesin these forward sections have multiplexed readout� i�e�� they have only one �ber perphotodetector pixel�

� In order to keep the calorimetric response between the near and far detectors as similaras possible� we plan to modify the design of the near detector modules slightly so thatthe calorimeter section of the near detector has a oneended light yield very close tothat of the sum of two ends in the far detector� To �rst order� this occurs naturally sinceWLS �bers in the near detector are shorter than those in the far detector� However�it may be desirable to include a crude mirror on WLS �bers in the near detector �e�g��white paint on the �ber ends� or to use slightly larger diameter �ber in order to makethe best match between the near and far detector light outputs� This will also ensuregood e�ciency for muons from the spectrometer section of the near detector�

�� Photodetectors �WBS ��

�� Photodetector requirements

MINOS neutrino events produce a wide range of light levels in the scintillator strips� Onthe low end� muons give at least �� photoelectrons from the lower of a strip�s two readoutends �at least �� photoelectrons from the sum of the two ends�� and the tails of showersrange down to single photoelectrons� On the high end� we want to maintain linear responsefor showering events with up to �� photoelectrons per strip on a single pixel� MINOSphotodetectors must meet this and other speci�cations

�� Linearity over a physics dynamic range of ��

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�� Ability to discriminate at �� of a pe level with acceptably low noise�

�� Shaping times � ��s to avoid pileup at the near detector�

�� Dark count below �� Hz�mm� of photocathode area�

�� Lifetime of � to � mC integrated charge and a failure rate of less than �� per year ofoperation�

�� Less than �� e�ect on gain for up to �� Gauss magnetic �elds�

�� Crosstalk between neighboring pixels � ��

�� Quantum e�ciency � collection e�ciency such that a muon crossing a strip gives atleast �� total pe�s observed on average�

�� Pixeltopixel nonuniformity of � � or better� Nonuniformity increases the electronicsdynamic range requirement�

�� Time resolution of better than � ns for signals of �� pe�s�

These requirements are met by several commercially available photodetectors� of whichmultipixel photomultipliers are the most attractive for MINOS� We have chosen the Hamamatsu R��U��M�� pixel photomultiplier for the MINOS baseline design because ofthe extensive favorable experience of other experiments with this photodetector�

�� Baseline photodetector

The baseline photodetector for MINOS is a ��pixel� multianode photomultiplier� R��U��M�� manufactured by Hamamatsu Photonics�� Our choice of the ��anode M�� isbased on two simple criteria a� R��U��M�� satis�es all our requirements� and b� amongall multianode photomultipliers it provides the lowest cost per unit area of the photocathode�The M�� tube behaves like �� miniature singlechannel phototubes� Only a few additionaland potentially adverse features� like crosstalk and nonuniformity of pixel response� areintroduced through dense packaging� Figure �� and Table �� show the geometry and basiccharacteristics of the M�� The R�� family of multianode photomultipliers includes tubeswith numbers of channels ranging from � to �� with independent anodes and metalchanneldynode structures� Hamamatsu maintains an active R�D program to improve performanceof the R�� series of tubes� The most recent example of this e�ort is development of animproved bialkali photocathode for the M�� tubes� which gives about a �� increase inquantum e�ciency over previously produced bialkali photocathodes�

The R��U��M�� tube has a wide range of applications� It is used in biomedicalimaging as well as in major high energy physics experiments� The HERAB detector atDESY uses �� of these tubes in the central part of the ringimaging Cerenkov counterreadout�� The upgraded Plug of the CDF II detector at Fermilab employs about ��tubes in the readout of the Preshower and Shower Maximum detectors��

Several high energy physics groups� including MINOS� have conducted many comprehensive tests on the M�� tubes during the last year�� These studies have provided valuable

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Parameter Description�Value

Photocathode material bialkaliWindow material borosilicate glassWindow thickness � mmSpectral response �� to �� nmWavelength of maximum quantum e�ciency �� nmQuantum e�ciency at �� nm �� Dynode type metal channel structureNumber of stages ��Anode an array of � � �

independent pixelsAnode dark current per channel � � nAPixel size � mm � � mm squareMaximum high voltage �� VGain at maximum HV ��

Nominal operating gain for MINOS ��

Anode pulse rise time �� nsTransit time spread per channel �FWHM� �� nsPulse linearity per channel �� deviation� �� mACrosstalk �� mm� aperture� � �Pixeltopixel gain variation � �

Table �� Basic characteristics of the R��U��M�� channel photomultiplier producedby Hamamatsu Photonics�

practical experience and allow us to project with high con�dence the performance of massproduced M�� phototubes� Also� the delivery capacity and reliability of the manufactureris now well established� In this Section we brie�y discuss selected features of the M�� tubewhich are relevant for the MINOS scintillator detector and associated electronics�

� Quantum e�ciency� The expected light yield for minimum ionizing particles requiresthat a photodetector be able to clearly separate single photoelectron signals from thepedestal� Since the emission spectrum of the wavelength shifting �bers peaks at about�� nm� and is further shifted to about �� nm due to length attenuation� we requirehigh quantum e�ciency for photons with wavelengths of about �� nm�

Figure �� shows a typical distribution of pulse heights obtained by pulsing a wavelength shifting �ber with a blue LED� Peaks of �� and � photoelectrons can be easilyidenti�ed� The new M�� tubes have an improved bialkali photocathode with a typicalquantum e�ciency of about �� at �� nm� as shown in Figure �� This constitutesa �� improvement over older tubes of this type�

� Pixel�to�pixel response uniformity� Studies by Hamamatsu� HERAB� and MINOSshow that individual pixels of the M�� tube can produce signi�cantly di�erent anode

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pulse heights for the same illumination� Figure �� presents an example of responseuniformity for one M�� tube� The gain of the inner pixels is typically lower than thegain of the perimeter pixels� About �� of channels are currently expected to exceed amaximum to minimum response ratio of �� This nonuniformity has no serious adversee�ects for MINOS� Its main impact is the increase of the dynamic range requirementon the frontend electronics� For MINOS� Hamamatsu guarantees the ratio to be lessthan ��

� Pixel response uniformity� Eight �� mm diameter �bers will be multiplexed ontoone �� mm� pixel� Although there are variations in intrapixel collection e�ciency�our measurements show that these are almost completely averaged out for �� mmdiameter �bers� Some pixels have intrapixel variations in gain for �� mm diameter�bers which are comparable to the interpixel gain variations� These intrapixel gainvariations can be directly measured for each �ber using our calibration system� andhave the same e�ects as the interpixel gain variations�

� Fast timing� We have measured the time resolution of the Hamamatsu M�� tube tobe better than � ns for greater than �� observed pe�s� Figure �� shows the measuredtime resolution for the Hamamatsu M�� tube as a function of the number of observedphotoelectrons� For these small numbers of pe�s� the time resolution is dominated bythe decay time of the Y�� uor in the WLS �ber rather than measurement e�ectsin these photodetectors� This timeof�ight measurement capability will be useful indetermining the direction of showering events induced in the MINOS far detector bycosmicray neutrinos� and is better than required for determining the direction of highenergy muons traversing the detector�

� Magnetic �eld sensitivity� The M�� tube is a proximity focused photomultiplierwith an additional electron focusing grid placed before the �rst dynode� This architecture assures relatively low sensitivity to magnetic �elds� In locations on the MINOSdetector in which photodetectors will be installed the expected magnitude of the fringemagnetic �eld is about � Gauss� Unshielded M�� tubes could typically lose about � to�� gain in such a �eld� However� magnetic fringe �elds could have a more seriouse�ect on cross talk between neighboring pixels� particularly for �bers located near pixeledges� To eliminate this e�ect� a thin soft iron sleeve �� mm thick transformer laminate� surrounds each MUX box� reducing the �eld at the photodetector by a factor of�ve or more�

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Figure �� Detail drawing of the Hamamatsu R��U��M�� multianode photomultiplier�

qvt charge

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Figure �� A typical pulse height distribution in a pixel of an M�� tube obtained by pulsinga wavelength shifting �ber with a blue LED� Peaks for �� and � photoelectrons are clearlyvisible�

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Figure �� A typical spectral response for a Hamamatsu R��U��M�� tube� For MINOSthe most important wavelengths are at about �� nm� the maximum of the emission spectrumof the wavelength shifting �ber�

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Figure �� A typical response of an M�� phototube� Each pixel was illuminated usinga � mm diameter wavelength shifting �ber with the same amount of light� On each pixelthe �ber was placed in � locations in a �� grid� The area of the squares in the plotare proportional to the signal on the anode� A pixeltopixel response nonuniformity� andvariation within one pixel� are clearly visible� The measurement showed that the observedstructure can be attributed mainly to the variation of the e�ective gain in individual channelsrather than quantum e�ciency or collection e�ciency� One corner pixel was not read out�

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Figure �� Time resolution �� measured as a function of the number of observed photoelectrons for the Hamamatsu M�� and DEP HPD reading out WLS �ber� The resolution forsmall numbers of pe�s is dominated by the decay time of the Y�� uor in the WLS �bers�Of particular interest is the better than � ns � for more than �� observed pe�s which will beuseful in determining the direction of showering events�

�� Connectors and multiplexing boxes �WBS ��

�� Fiber connectors

Construction of a modular detector requires e�cient and coste�ective �berto�ber connectors� In MINOS� optical �ber connectors are used to couple the WLS �bers coming fromthe scintillator modules to the clear�ber ribbon cables and between the ribbon cables andthe multiplexer boxes� Such connectors have already been developed for the CDF endplugupgrade �� bers�� the D� upgrade �about �� bers�� and recently for the CMS HCAL ��bers�� Tests on these connectors have shown similar performance in light transmission� ForMINOS� we are planning a customdesigned connector based on one of the previous designs�The MINOS connector will be a ��wide connector with �� mm pitch for the �bers� �Thisis most similar to the CMS connector which is �� wide and with �� mm �ber pitch�� Thereason for designing a custom connector rather than just using one of the existing connectordesigns is cost� To a good approximation� the cost per connector and manpower to assembleit is the same regardless of the design or the number of �bers included �up to some reasonable limit�� Furthermore� the cost of clear �ber ribbon cables is much lower if a pitchof about � mm is used rather than a pitch of about � mm as for previous cables� We arecurrently evaluating the di�erent connector designs to decide which is optimal for MINOS

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needs� We have used both ��wide CDF connectors and prototype CMSstyle connectors inconstruction of MINOS prototype modules� We �nd similar results for light transmissionfrom the two types of connectors�

A sketch of a MINOS connector at a ��wide scintillator module manifold is shown inFigure �� The connector is wide enough to accommodate �� optical �bers in order toallow just one connector design for all modules� The � unused �ber positions are pluggedwhen the connectors are used for ��wide modules� Appropriately matched connectors arelocated on the scintillator manifolds� the MUX boxes and each end of clear �ber ribboncables which connect the two� MINOS ribbon cables are �� and � �bers wide �these arealready a custom production so there is no problem specifying these widths�� Fibers areglued into the connector housing with epoxy� with a few mm of the �ber left protruding�The protruding �bers are �y cut and polished using a diamond �y cutter� Prototype ��wideconnectors are currently being produced for MINOS�

scintillator plastic extrusions

WLS fiber #1

WLS fiber #20

light

connectoroptical28-wide

injectioncaselightbottom

compartmentmanifold

Figure �� Sketch of a MINOS ��wide optical connector for �� mm diameter �bers� asused on the end manifold of a ��wide scintillator module�

The CDF connectors were manufactured by the DDK company of Japan�� CDF hasmeasured the light transmission across the connector without optical coupling� The meanof the measured light transmission is �� with small spread� Out of the total lightloss of �� is expected from the Fresnel re�ection� The light loss can be reduced byusing optical couplant� The DO collaboration has measured an average light transmissionof �� using a di�used light source and �� using a small angle light source�� fortheir tracker and preshower detector for the upgrade� but with use of an optical couplant�

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CDF has measured the reproducibility of the light transmission for this connector throughmultiple repetitions of disconnecting and reconnecting� The rms width of the distributionis less than �� Our �rst test results show that MINOS connectors will provide similarperformance�

�� Multiplexing boxes

The multiplexing �MUX� box is the link in the readout chain between the signal �bers andthe photomultiplier tubes� as shown schematically in Figure �� The mechanical structureof the MUX box is shown in Fig� �� The input signals from the detector are brought tothe MUX box by clear optical �bers� bundled into ribbon cables� that plug into bulkheadconnectors on the front plate� Inside the MUX box� clear �bers are mated to the signal�bers and then routed to the back plate through an aluminum box chassis� At the backplate� the �bers are laced to three internally mounted cookies that are machined to alignprecisely with the pixels of three ��channel PMTs� The MUX box is designed to be lighttight and is shielded against magnetic fringe �elds�

External to the MUX box on the back plate� the cookies are mated to the PMTs bymeans of a PMTcookie assembly� This assembly� shown in Fig� �� allows for the removal�replacement of a PMT without opening the MUX box� In this design� the cookieremains in a �xed position with respect to the cookie holder� To allow for tolerances in themanufacture of its case� the PMT is cemented into an outer jacket� This jacket �ts preciselyinto a holder that permits pistonlike motion with respect to the cookie but very little lateralmotion� The pistonlike motion enables the springloaded PMT base to push this assemblyinto contact with the cookie� The precision alignment of the cookie with the PMT is accomplished by aligning the cookie holder with the PMT holder using a special alignment tool�the alignment procedure takes place in the lab� away from the detector�

The three PMTcookie assemblies are bolted to the back plate and housed in a lighttightPMT cover box� The electronics are connected to the PMT outputs through the PMT coverbox�

There are �� MUX boxes in the MINOS far detector� The far detector makes use of ��multiplexing on the PMT pixels while the near detector will make use of �� multiplexingin the muon spectrometer section and no multiplexing in the target�calorimeter section�However� the same design for both the MUX box and electronics will be used for the neardetector� Near detector MUX boxes have fewer connectors on their front plates� fewer �bersto be routed� and special cookies to accommodate the particular number of �bers in eachtype of box� There are a total of �� MUX boxes in the near detector�

� Mechanical construction of the MUX box

All MUX box components shown in Fig� �� are stamped and formed from sheetaluminum� The boxes are assembled with stainless steel selftapping sheet metal screws�Each box is surrounded by a � mm thick sleeve of soft iron transformer laminate toshield the photodetectors against magnetic fringe �elds �not shown in Fig� ��

The inputs to each MUX box are �� mm diameter clear polystyrene �bers carryingthe signals from two consecutive detector planes with the same stereo view� These ��signal �bers are bundled in ribbon cables� Each of these ribbon cables terminates in

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Figure �� MUX box assembly� The external magnetic shield of � mm thick soft iron whichsurrounds the box is not shown�

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Figure �� PMTcookie assembly�

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a �ber optics connector �see Section �� that plugs into a double female bulkheadconnector mounted on the MUX box front plate� Inside the MUX box� groups of eightclear �bers mate to the signal �bers through the front plate bulkhead connectors� Ahole is provided near the bottom of the front plate to mount an LED and di�user onthe inside of the MUX box� as described in Section �� The internal signal �bersare routed from the front plate� through the box chassis� to the cookie on the backplate� The ��cm length of the MUX box chassis is set by the requirement that thebend radius of the �bers be greater than �� cm�

� Routing and �y cutting �bers

The �� signal �bers are routed to three Hamamatsu M�� multichannel PMTs throughprecisionmachined cookies� Eight �bers are routed to each � mm � � mm pixel� Twoof the PMTs in a fardetector MUX box see � � �� bers from single planes�the third PMT sees � � � � �� bers from each plane� The ribbon cable connectorsare inserted into the front plate according to a pattern that minimizes �ber lengthswithin the MUX box�

The baseline detector has �fold multiplexing and �ended readout� To resolve ambiguities introduced by the multiplexing� the two strip readout ends will have di�erentrouting�lacing schemes� On a single pixel� �bers arrive from each of the eight logical modules within a scintillator plane� The exact scintillator strip location �withinthe logical module� to pixel location map is permuted within groups of eight �bers�Monte Carlo simulations of neutrino events show that this mapping permits unambiguous identi�cation of the true location of neutrino events for light levels meetingour speci�cations�

For cookie assembly� the �bers are �rst glued into the connectors� Then the connectors for a group of �� bers are �xed to a jig and the �bers routed to the cookieaccording to the appropriate permutation scheme� To facilitate accurate routing toa particular cookie position� the �bers are illuminated with the same programmableLED sources used for quality control checks �see the �nal bullet in this Section�� Aftergluing the connectors and cookie are �y cut with a commercial �y cutting machine�The procedure for inserting the �bers into the connectors and then lacing the cookiewas developed for CDF� However� for MINOS the procedure for routing the �bers tothe appropriate cookie hole is more complicated than for CDF� We have begun to optimize this procedure by actual prototype assembly in order to estimate the manpowerrequired�

� PMT�cookie assembly

The PMTcookie assembly is shown in Fig� �� The cookie is injection molded fromgrey Noryl and mounted inside the MUX box on the back plate� It has �� precisionholes that accommodate �� mm �bers in a �� pattern �three �bers on top andbottom with two �bers in between� arranged in a closepack array�� The cookie holesprecisely align with the �� pixels on the PMT� The cookie mates with a cookie holderoutside the MUX box� The cookie holder has a central hole with the exact shape ofthe cookie and is attached to a PMT holder using slightly oversized holes� These holes

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allow the cookie to be accurately aligned with the pixels on each individual PMT� Thisalignment is done in the lab using a special clear acrylic �alignment cookie� with theexact shape of an actual cookie� Both the cookie and the alignment cookie have socketsfor two alignment dowels that rigidly �x the cookie and the alignment cookie in thesame position relative to the cookie holder to within tolerances of a few thousandths ofan inch� The alignment cookie has precision ruled marks that accurately line up withthe guide marks on the PMT photocathode� The cookie holder with the alignmentcookie is accurately aligned with the PMT holder before they are rigidly �xed to oneanother�

The PMT is pressed against the cookie� pistonlike� by a springloaded base� The PMTis glued into an aluminum jacket that allows for the �� mm tolerances on the PMThousing� The outside of the jacket is precisely machined to �t into the PMT holderin a way that allows it to slide without lateral motion� The PMT base is attached tothe PMT holder� The cookie holder� PMT holder� PMT� and base assembly are thenattached to the cookie� A lighttight housing is placed over the PMTcookie assemblyand bolted to the back plate�

� QC computer controlled LED array

Final checkout of the lacing scheme and the MUX box will be made using a programmable set of LED sources� A set of patterngeneration LED boards is driven bya computer� Clear �bers from the LEDs run to optical connectors which couple to theMUX box connectors� To test the lacing pattern on a cookie �a� each of the lacingschemes is programmed into the computer� �b� individual �bers are illuminated in sucha way that only one �ber in each of the �� pixel holes on the cookie lights up� simplepattern recognition is performed by eye� �c� the test is then repeated � times for eachcookie� The completed MUX box will be tested with this computer controlled LEDarray by �ashing attenuated LED signals through each �ber and measuring the PMToutput�

This testing device is also used to facilitate �ber lacing� For this task� the QC computeris programmed to illuminate the � �bers that are to be routed from the connectors toa particular pixel hole on the cookie� By plugging and gluing only lighted �bers� �berrouting becomes simpler� more accurate� and less time consuming�

�� PMT bases and mounting

The M�� photomultiplier and its mounting brackets are rigidly attached to the back plate ofthe MUX box� A square opening in the plate lets the �bers couple to to the photocathodeface� The tube is aligned with �bers as described in the preceding Section� The PMT base�voltage divider board� is mounted directly on the pins of the tube� For strain relief thisboard is also attached to the PMT holder using � spacer screws placed in the corners of theboard� The entire phototube assembly �i�e�� a cookie� a cookie holder� PMT holder� PMT�and the voltage divider card� is housed in a lighttight case sealed to the back plate of theMUX box�

A multipurpose feedthrough Dtype connector on the PMT housing supplies HV tothe photomultiplier and also carries �� anode and one common dynode signals� The three

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PMT connectors on the MUX box are aligned to mate directly with connectors on thefrontend electronics card� The PMT base provides a negative high voltage bias for thedynode structure and also routes the anode signals� �Tapered� resistor values allow a gainof about �� up to � mA anode current� and response linearity of �� over the entirerange of physics and calibration pulses� Heat generated by the divider current �� W for�� A at the maximum high voltage of �� V� is easily dissipated by the PMT mountingstructure and the multiplexing box� This arrangement mechanically decouples the frontendelectronics board from the photomultiplier and at the same time provides a short signal pathand good noise shielding�

�� Calibration systems �WBS ��

The calibration system provides the means of understanding the calorimetric response ofthe near and far detector for hadrons and electrons and ensuring that the relative responsebetween the two sites is understood� The goal is to calibrate the hadronic energy responseto an absolute level of �� and a relative level of �� between the near and far detectors�This requires several di�erent calibration systems as described in the following Sections�Cosmicray muons provide an integral part of the system� The calibration plan is discussedin Section ��

�� Laser light distribution

The baseline design for the MINOS light injection system uses UV laser light sources� Thelaser light illuminates scintillator blocks surrounding sets of eight or ten WLS �bers� Thisensures a good match between the spectrum of light from the calibration system and thescintillation light from real neutrino events� The advantages of a laser system are

� The laser pulses are extremely short �� ns� so that the time pro�le of the pulsereaching the PMT is dominated by the WLS dyes� This makes calibration pulses verysimilar to those from a particle�

� Optical �lters are used to attenuate the light at wellcontrolled prede�ned values�

� With one laser it is possible to illuminate � �� WLS �bers at once� so only a smallnumber of lasers is needed�

The far detector requires a single laser coupled to an optical �ber routing network whichis used to inject light into the light injection manifolds described earlier� The pulses from thelaser can be directed under computer control to distribution points located at the corners ofeach supermodule as shown in Figure �� The placement of the components is designed tominimize the lengths of �ber in the system� Figure �� shows a schematic for the distributionnetwork� The laser which pulses the system is a N� laser which can deliver several hundredmicrojoules per pulse at a wavelength of �� nm� Each laser feeds a distribution systemof splitters and �bers allowing it to pulse �� i�e�� one physical light injector module perplane� of each detector block in a given view at a time� This results in only one �ber ata time being pulsed on each photodetector pixel� The laser is equipped with a computer

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controlled attenuation wheel� containing neutral density �lters� to provide a wide dynamicrange for test calibration� A gainstabilized reference photodetector monitors pulse to pulsevariations of the laser output� To ensure the stability of the monitor photodetector� it alsoviews a NaI�Tl� crystal with an imbedded ��Am source� The laser light is transported tothe fanouts by quartz �bers� and between the fanouts and the scintillator modules by acrylic�bers� This provides acceptable attenuation at reasonable cost�

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MINOS supermodule

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Figure �� Location of components for the laser calibration system�

A similar lightinjection system is being implemented as part of the CDF plug upgrade��The CDF laser produces approximately �� photons per pulse� The overall light delivery e�ciency of the CDF system is � �� This includes coupling to the �berfrom the laser� light loss in transmission� light loss in the primary distribution to the splitterboxes� loss of light inside the splitter boxes� laser light dumped in a scintillator block� scintillation light coupling to WLS �bers� and light coupling to the PMTs�� In the system weare planning� we have essentially the same set of steps in our light delivery system except forthe losses of light due to transmission in acrylic �bers instead of glass �bers� Both CDF andMINOS use the same Hamamatsu PMT� In CDF� there are �� photons reaching thephotocathodes through approximately �� bers� Folding in a �� QE in the PMT anddividing out the �ber count� results in �� pe�s per �ber� which will be enough lightfor the high energy end of the calibration�

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1:128 Fiber Fanouts

1:20 laser beam splitter

to individual scintillator modules

scintillatorlight injection

scintillator module

Nitrogen Laser

from opposite sidelaser system

Attenuationwheel

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Figure �� Schematic of the distribution network for the laser calibration system�

It is not necessary to have complete uniformity in the light injection system as long asthe illumination is constant over time� Di�erences in intensity of up to �� are acceptableacross the WLS �bers within a manifold� Di�erences of up to a factor of two are acceptablefor the amount of light arriving at completely di�erent photodetectors� �More light settingsare then required to get a complete calibration��

�� Light injection to photodetectors

A green �� nm� ultrabright LED is installed in each MUX box to help isolate lighttransmission problems in the readout chain� The LED is pulsed at a low voltage levelto check the response from all pixels of the three photodetectors simultaneously�

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�� Radioactive source system

The purpose of the source system is to obtain a rapid measure of the response of eachscintillator in the detector� Short stainless steel tubes are attached at either end of a detectormodule as described in Section �� A tube acts as a guide track for a � mC ��Cs sourceattached to the end of a piano wire� The source position is controlled by a drive mechanismunder computer control� Modules are scanned with the ��Cs wire source at the time ofassembly and installation� When the detector comes on line to take data� the movablesource can be used to verify other calibration methods or to troubleshoot� We do not planto perform source scans on a regular basis� so only two source drivers are needed at eachdetector site�

There are two source tubes per module� one at either end� The ��Cs source is insertedinto the source tube via a plastic funnel tube that is connected �temporarily� to the sourcetube and runs back to the ��Cs storage unit� Source tubes traverse all of the scintillators ina module within �� cm of the scintillator ends� The source tube at the endcap is positionednear the right edge of a module� It runs parallel to the strip direction in the endcap� but asthe tube reaches the scintillator strips it is bent with a �� cm radius across the strips� Aftera bend of �� the source tube traverses the remaining scintillator strips in the module in astraight line� This permits all strips to be illuminated in approximately the same locationand keeps the bend radius large enough so that the source will not stick in the tube�

�� Calibration module

The calibration module is essentially a �test beam calorimeter� built with �nal productioncomponents� This detector will be exposed to hadrons� electrons and muons using theplanned Main Injector test beam at Fermilab in order to determine the absolute light responseand energy resolution for hadronic and EM showers� The initial module will use summedoutputs from detector planes to provide the necessary calibration at low cost� Most of thecomponents� except for the steel and scintillator planes� will be spares from the near andfar detectors� If oscillation signatures are observed� further understanding of details of theresponse and resolution can be obtained by upgrading the calibration module with the fulltransverse instrumentation as in the near and far detectors� The module will be transportablein order to crosscheck the response of muons in the module at the di�erent detector sites� ifdeemed necessary� The module will be equipped with a source and light calibration devicesas in the main detectors�

The features of the proposed initial calibration module are

�� The module has �� layers of steel� each layer being �� cm in thickness� The totalthickness of iron is �� cm or �� interaction lengths� The number of layers has beenset based on the containment of showers from �� GeV pions�

�� The dimensions of the calibration module are �� m �longitudinal� by �� m �transverse�and �� m �height� with a rectangular cross section� The transverse dimensions havebeen set to permit containment of events� even with the detector axis rotated by up to�� with respect to the beam axis �assuming �� cm o�set to one side for the incidentbeam��

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�� The detector weighs about � tons�

�� There are �� layers of scintillator strips with �� strips per detector plane� All featuresof the scintillator strip assemblies mimic the construction of the near and far detectorin order to ensure the same response to showers� The orientation of the scintillatorstrips is rotated by �� in successive planes�

�� Clear �ber ribbon cables transmit light to MUX boxes and photodetectors as in thenear and far detectors�

�� The photodetectors are identical to those used in the near and far detectors� Thescintillator strips are read out at one end� The output of � neighboring strips in eachdetector plane are multiplexed onto a single pixel of the photodetector� Hence� a totalof �� pixels are required for the full detector� corresponding to � phototubes�

�� Cosmic ray muons

The MINOS near and far detectors experience a �ux of high energy muons produced highin the atmosphere in primary cosmic ray interactions� They o�er the possibility of directcalibration in the low energy range of the MINOS scintillators using minimum ionizingparticles� There are two principal questions First� are the rates of these muons adequatefor calibration� especially at the deep location at Soudan Second� are there signi�cantdi�erences in the energy deposited in the scintillators at the two locations due to the di�erentmuon energy spectra and angular distributions

The rates and angular distributions of the underground muons at Soudan are wellknown�� Using these� we have calculated the �ux and the muon path length distributionthrough a single � m long MINOS scintillator� � cm � � cm in crosssection and orientedat �� to the horizontal� The muon �ux is is �� per month� The �ux in the neardetector will be �� to �� times greater� The distribution of muon path lengths throughthe scintillator strips shows a well de�ned peak with median value �� cm� Ten percent ofthe muons will have a path length greater than � cm�

The energy deposited in the scintillator strips is dependent on the muon energy spectra�This dependence can arise from the relativistic rise in dE�dx ionization loss as a functionof primary energy� and also from di�ering bremsstrahlung� deltaray� and pair productionalong the track of the muon� We have estimated the di�erence in average muon energy atthe near and far detector halls� The median muon energy at Soudan � depth is �� GeVand at Fermilab it is �� GeV� We have estimated the average energy deposition rate inplastic scintillator due to ionization as a function of energy� Averaging over the muon energydistribution� we estimate that any di�erence between the two depths will be less than ��The probability of delta rays accompanying the muon is essentially energy independent and�indeed� is already accounted for in the the ionization prescription� Hence� the main concernfor possible calibration di�erences are due to bremsstrahlung and pair production in the steelwhich sends extra particles into the scintillator strips�

The probabilities of bremsstrahlung� and pair production in the steel of the Soudan �detector have been calculated previously�� Energy losses via bremsstrahlung and pairproduction are strongly dependent on the muon energy� The former tends to produce large

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bursts of energy relatively infrequently along the muon path� These electromagnetic showershave been studied in the Soudan � detector and will produce extremely large scintillatorsignals less than �� of the time� They can be removed by a simple cut� However� the pairproduction process require more study�

We have made a MonteCarlo calculation of photoelectron yields for muons at Soudan�based on the known angular and energy distribution of those muons and observed light outputdistributions for cosmicray muons in our prototype scintillator strips� Poisson statisticshave been assumed for the observed photoelectron distribution� By calculating the mean ona truncated distribution� the MonteCarlo calculation suggests that the light output of eachscintillator strip can be calibrated to a precision of �� in � month� In order to verify theseestimates� we are undertaking a series of measurements at di�erent depths underground�using scintillator strips located between � cm steel sheets�

Ultimately� if necessary� we can check the muon calibration at the di�erent detector sitesusing the transportable calibration module� Finally� about �� of the muons stop in thedetectors� These will provide a source of muons of known energies �using range to determineenergies� to provide another crosscheck on the calibration�

�� Calibration plan

The goal of the calibration system is to permit the translation of the measured hadronicand EM shower response from a test beam to the near and far detectors and over the fulltimeperiod of data acquisition�

The calibration module will be used to obtain calibration data in a chargedparticle testbeam at Fermilab� Cosmicray muon data will be used to transport the calibration to thenear and far detectors� The rate of cosmic ray muons is su�ciently low �especially at Soudan�that it is important to keep track of gain changes in the system over a shorter time scale� A�� calibration for each far detector scintillator strip is possible with one month of muon dataand an equivalent amount of data from the calibration module �at Soudan� will be required�

The near and far detector light injection systems provide the ability to track shorttermgain changes and to measure the response curve to light of the full PMT�electronics systemfor each �ber independently� For each channel� a set of constants will be produced comprisinga pedestal and one or more constants describing the shape of the light in�light out curve�The muon data provide a common �xed point in the light response curve for each �ber�The lightinjection system also permits localization of any anomalies in light transmissionthrough the �bers and connectors� The electronics is tested independently by direct injectionof charge �see Chapter ��

The above procedure provides a complete set of calibration information� However� wealso have some crosschecks on this calibration� During installation the individual stripsare tested with the ��Cs source� This provides both an important debugging tool and acrosscheck on the muon calibration of light output� At the near detector� throughgoingmuons from neutrino events provide an independent data set for calibration� Finally� wecould choose to operate the calibration module at the near detector site to obtain neutrinoevents� In this case� there will be a su�cient number of neutrino events in the calibrationmodule to make a direct comparison of hadronic energy in those events to hadronic energyin the near detector target�calorimeter region�

��

�� Assembly and testing equipment �WBS ��

Construction and testing of scintillator modules requires several specialized machines whichare described in this Section�

�� Extrusion trimming machine

The extrusion trimming machine is used to cut the length of each scintillator strip to atolerance of � mm� The trimming saw is a stock commercial cuto� saw equipped with a �neblade and an ��m long custom cradle� This scintillator strip cradle has a graduated slideto enable a technician to quickly and precisely set the �nal length of the extrusion�

�� WLS �ber gluing machine

This Section describes the machine which glues WLS �bers and re�ective groove covers to thescintillator strips using a commercial glue dispensing system� The operation of the machinein production mode is described in Section �� Figure �� shows the conceptual designfor the gluing machine� The machine performs three completely automated operations onscintillator strips in one pass� It lays a bead of optical glue in the extrusion groove� placesa WLS �ber in the glue bead� and lays the re�ective extrusion groove cover over the �ber�

The machine requires operator assistance to set up a WLS �ber in an extrusion prior togluing� and to cut and set the �ber after gluing� The machine transports strips lengthwiseunderneath three work heads� Scintillator strips� which have already been cut to length�are fed to the gluing machine from preloaded magazines� Magazines are used to provide acontinuous supply of strips to the glue machine with minimal operator intervention�

Glued strips coming o� the glue machine are placed in a curing rack which containshorizontally indexable shelves� each holding the �� or �� strips needed for a single module�After gluing the strips for one module� the operator adjusts the height of the curing rack tobring an empty shelf into alignment with the exit of the gluing machine�

The WLS �ber gluing machine contains �ve functional modules a glue dispenser� aWLS �ber unwind stand� a re�ective extrusion groove cover unwind stand� an extrusion feedmechanism� and a central programmable logic controller �PLC�� In addition� the machineincludes three auxiliary modules to perform quality control and inspection functions� The�rst auxiliary module checks for cracks in the WLS �ber cladding� the second measures thewidth of the scintillator strip at several points along its length� and the third tests the lightoutput of the scintillator by shining a UV light into the groove and measuring the blue lightemitted�

A commercially available glue dispensing system mixes the two parts of the glue in a specially designed disposable dispensing nozzle �replaced after each shift�� The glue dispensingsystem meters the resin and hardener glue components �supplied from �ve gallon buckets�and is insensitive to variations in viscosity�

The WLS �ber and re�ective groove cover unwind stands are equipped with commerciallyavailable tension controllers� The PLC matches the length of the glue bead dispensed to thelength of the strip being processed� The central PLC controls both the glue dispenser andthe unwind stand tension controllers�

��

Conveyor Belt

Tension Sensors

Glue Dispensing Head

Tape Roll

Fiber Roll

Figure �� Conceptual design for WLS �ber gluing machine�

��

The curing rack holds the �� strips required for one shift of assembly� The �lled rackis moved to the assembly area when the glue has cured and the extrusions are ready forassembly into modules�

The WLS �ber gluing machine has a special accommodation for strips interrupted by themagnet coil bypass hole� The machine is equipped to glue one continuous WLS �ber acrosstwo extrusion sections� each approximately � m in length� for these modules� A dummysection of extrusion� matching the free �ber length required to clear the bypass hole� istemporarily placed between the two extrusion sections� The PLC shuts o� the glue supplyas the dummy section passes beneath the glue dispenser� The dummy section is removedafter the glue cures� leaving the correct length of WLS �ber for routing around the bypasshole�

�� Scintillator��ber gluing templates

The WLS �bers extend for some distance �enough to reach the optical connector� past eachend of each scintillator extrusion� so the �ber extensions must be protected during gluingand handling �prior to installation in the module�� Each scintillator strip is placed in analuminum channel which is just large enough to hold the strip� In addition� extra pieces ofactual scintillator strip are placed at each end of the strip being worked on� The end piecesare customlength �tools� which hold the extra �ber �without glue� while the glue in thecenter strip cures� The entire assembly is run through the glue machine and the end piecesof scintillator are used to determine when to start and stop the glue �ow� The �bers areclamped at the outside ends to hold them in place while the glue is curing� The very end ofthe �ber will be cut o� after installation in the module and does not need to be protected�

�� Light case rolling machine

The module factory is equipped with a rolling machine to form the aluminum light case Uchannels� The machine allows the aluminum sheet for the light cases to be purchased inconvenient roll form�

�� Module assembly tables

The module factory is equipped with two equivalent module assembly tables� The tablesprovide �xturing for technicians to manually assemble modules accurately and e�ciently�The module assembly is done in two main stages� In the �rst stage� a bottom light caseis placed on a support tray� scintillator strips placed in it on top of a glue layer� �bers arerouted through the end manifolds and potted into connectors� and the top light case putinto place on top of a second layer of glue� This assembly is sealed between two sheets ofMylar and evacuated with a mechanical vacuum pump in order to compress it uniformlywhile the glue sets� Following this� the modules are left overnight to allow the glue to curecompletely� The following day� the aluminum case is crimped to produce a lighttight seal�the top manifold cover is installed� the manifold edges are glued� and the connectors are cutand polished�

��

�� Assembly table glue mixing machine

Substantial quantities of epoxy must be mixed to glue the scintillator strips to the top andbottom U channels of the light case� More epoxy is needed to glue the source calibrationtubes to the light case� One automatic glue dispensing machine mixes the glue for bothassembly tables� The machine has a mixing nozzle similar to that used on the WLS �bergluing machine� but it is used only to supply precisely mixed batch lots of glue in disposablecontainers�

�� Optical connector polishing machine

A portable �y cutting machine is used to face the optical connectors utilized in the endmanifolds of each module� Our application requires only minor modi�cations to the holding�xture of an existing Michigan State University machine to conform to MINOS connectors�The machine consists of a precision electrical motor with a �y cutter attached to its spindle�This assembly is a�xed to a dovetailed linear slide driven by a pneumatic piston� The �ycutter passes at right angles to a tool holder which grips the optical connector�

�� Curing racks

The module factory requires two styles of curing racks� The �rst holds groups of individualstrips after they exit from the WLS �ber gluing machine� as described in Section ��The second type of curing rack holds up to six trays that support assembled modules whilethe structural glue is curing�

Two sets of racks are required per shift� One set is �lled with newlyglued componentsfabricated during the shift� The second set has strips or modules which were glued theprevious day and are ready for the next steps in assembly�

�� Module mapper

The light yield due to variation in scintillator light output� attenuation length of WLS �bersand features of assembly could vary from batch to batch� Therefore it is important to quantifythe response of each scintillator�ber element within a module following the assembly� Thismap will be used for future understanding of the module performance and allow rejection ofany modules which have poor response features� Furthermore� we will provide the capabilityto subject modules to a �quickscan� at the detector sites prior to installation onto steeloctagons in order to ensure that no damage has occurred during shipping and handling�

The module mapper is an automated device which consists of a large �at table with acollimated ��Cs source that can be moved quickly to any location over the surface of themodule� The response over a predetermined xy grid will be measured for each moduleimmediately following assembly� The source is located � mm above the module�s skin� Thedistance between source and module skin will be controlled by a feedback mechanism�

Drawings of the module mapper are shown in Figures �� and �� The source is drivenin two orthogonal directions the long direction spans the full length of scintillator stripsand the short direction spans the module width� The drive mechanism positions the source

��

Figure �� The module mapper� The top and side views of an � m long scintillator moduleare shown�

Figure �� End view of mapper shows details of scanning device and the source containerat two extreme positions�

with an accuracy of �� mm in the short direction and �� mm in the long direction� Drivespeed is �� cm�s in the long direction and �� cm�s in the short direction�

Calibrated photodetectors are read out by the same processor that controls the sourceposition� The response of each scintillator strip will be measured every �� cm �or less�if necessary� along its length at the assembly factory� The capability will be provided toperform a quickscan at the near and far detector sites using the module mapper� Thiswill permit checks of module integrity following shipping as deemed necessary based onexperience�

The response maps of each module will be entered in a database� As a crosscalibration�a radioactive source �see Section �� will be inserted into the calibration tube at eachmodule end and the response recorded in the database� This will permit an easy check thatthe module performance after installation in the detector is the same as when it was mapped�

��

�� Module factories �WBS ��

The scintillator modules could be produced at a single production site running two shiftsper day� However� we expect that the optimal production scenario will include two factory locations for module production� This permits faster production �and provides someschedule contingency� and e�cient use of collaboration resources while keeping costs low�The layout and materials �ow plan of the module factory are shown in Figure �� Theboxes correspond to the machines described in Section �� The arrows indicate the �owof module components between machines� Each factory will have a seven person crew andwill produce an average of four modules per shift� Module assembly tests have veri�ed thatthis is a realistic rate for production� The following Sections describe factory operations inthe order indicated in Figure ��

�� Prepare scintillator strips

Scintillator strips are purchased in several lengths and are �ne cut on the factory �oor�Trimming is especially important for �� angled modules� where the length of every extrusionin the module is di�erent� During the trimming� the extrusion is visually inspected for anysigns of external damage� The trimmed strips are loaded into magazines used to feed theWLS �ber gluing machine� Handling� inspection� trimming� and loading time is estimatedat � minutes per extrusion�

�� Glue WLS �ber and re�ective cover to extrusion

The WLS �ber gluing machine is operated by one technician� The gluing machine is fedby magazines of �� to �� strips to reduce the labor of loading each extrusion individually�Furthermore� the magazines help to preserve the order of strips cut to di�erent lengths�Gluing templates with clamps are used to keep the �bers in place during glue curing andwhile feeding the strip through the machine� These also keep the scintillator piece frommoving during the necessary handling� The machine glues the WLS �ber and attaches there�ective groove cover for the length of the extrusion� Once the �ber is glued and clamped�it is rough cut to an appropriate length beyond the end of the strip� The glue machineis also designed to test the quality of the �ber and scintillator strip as each pass throughtest points� prior to gluing� The average gluing time for each extrusion is estimated at twominutes per extrusion�

�� Prepare light case U channels

The light case U channels are formed from a roll of sheet aluminum using the light case rollingmachine described in Section �� The same machine is used for both the bottom and topU channels� The width of each light case can be adjusted to accommodate di�erent widths ofscintillator strips used in each module� The total time required for all operations associatedwith the rolling machine is estimated at �� minutes per module� Rolling operations areperformed by the same technician that operates the extrusion trimming station�

��

Extrusioncuring rack

WLS fibergluing machine

END

Extrusiontrimming station

START

storage

glue mixingmachines

Moduleassembly table

Moduletable

Cured extrusions

Moduleassembly table

Assembly

curing rack

Moduletesting bed

Packing crateloading platform

Packing crate

Modulecuring rack

Cured modules

rolling machineLight case

Figure �� Floor plan of equipment layout and materials �ow in module factory�

��

light case (ULC)

Remove fiberprotective fixtures

from ends ofextrusions

Attach upper

in LLC

Punch manifoldmounting holes

in LLC

Attach end manifold

Place extrusionsPlace thelower light case (LLC)

in module assembly tray

Apply glueto inside face

of LLC

bases

Movemodule tray

to curing rack

Apply vacuumfixturing

extrusions

Route fibersin end manifolds

Pot fibersin bulk

optical connectors

Apply glueto top of

Figure �� Flow chart of module assembly operations performed at the �rst stage of moduleassembly�

�� Assemble strips in light case and route �bers

The �rst step to assemble a complete module is to glue the strips into the aluminum lightcase and route the WLS �bers in the manifolds to the bulk optical connectors� The moduleis compressed using a vacuum table while the glue sets� and is then left overnight to allowthe glue to cure completely� A �ow chart of operations required for this stage is providedin Fig� �� Most operations are selfexplanatory� Two technicians are required for theoperations in this step� Fibers are routed into the manifold and connector as each strip islayed into the bottom light case� This helps to keep �bers in order and protects them fromdamage� This step requires about one hour per module�

��

fibers in bulkoptical connectors

Apply bar codeto module

Fly cut and polishSlide thelight case out of

module assembly tray

light case

Seal allend manifold joints

with RTV

edges of theAttach

manifold cover andvariable width seal

Crimp thePunch manifold

end manfolds

mounting holes inupper light case

Glue source tubesand guards below

Figure �� Flow chart of operations needed to complete module assembly�

�� Finish module assembly

Once the glue in modules has been allowed to cure overnight� the steps needed to �nish themodule assembly are done� A �ow chart of operations required at this stage is provided inFig� �� Most operations are selfexplanatory�

The portable optical connector polishing machine described in Section �� is used toface all optical connector plugs in one module� The operations in this step are estimated torequire a total of one hour per module

�� Source map module and light�leak check

Completed modules are moved to the sourcemapping table for checks for light leaks andmapping with the radioactive source� Light leaks are detected by anomalously high countrates using slightly higher than normal ambient light levels� Any leaks are located usinga bright local light and covered� When the module is light tight� the automated mappingmachine is started and runs on its own� Each strip of the module is mapped at �� cmintervals along the length� The computer controls the source location and collects datawhich are stored for future reference� Finally� the wire source is inserted at each end toestablish the light yield response of the module for this source at the time of production�

�� Packing and shipping of modules

Shipping crates will be of a very rigid construction� fabricated from a combination of angleiron� �� mm diameter steel rods� and plywood sheets� The de�ection of the crates whenpicked up from the ends is approximately � mm� Modules are supported in the crate hori

��

zontally� It is estimated that the modules can easily handle de�ections of up to �� cm overtheir length� The total weight of the largest crates and modules is approximately �� lbs�There are two types of crates� one for each module width� with di�erent lengths for near andfar detector modules�

The crates will be insulated with � cm thick styrofoam which provides cushioning to themodules and insulates them from temperature extremes� It is expected that modules will befabricated and shipped in temperature controlled conditions� However� during the transferof crates from temperature controlled trucks to the underground entrance shaft� some cratesare likely to be brie�y subjected to temperatures as cold as �� C� The insulated crates willprevent any possibility of damage during this transfer�

A total of �� crates are needed during peak production and installation times to permitbu�ering of production and storage of modules at the near and far detector sites awaitinginstallation� The maximum weight that can be transported on a standard semitrailer is�� lbs� thus limiting each shipment to six fullsize crates� Trucks delivering modules willpick up empty crates for delivery back to the module production factory�

�� MUX box assembly

The MUX boxes for MINOS will be assembled at two sites� These sites will require onlya small amount of specialized equipment a �y cutting machine� a computer controlledLED array and three PMTs for testing the boxes� Other equipment is assumed to existat established laboratories� The MUX box front plate� chassis� chassis cover� back plate�and PMT cover box will be stamped and formed at a sheet metal shop� The cookie� cookieholder� and PMT holder will be fabricated by computer numerically controlled machines�The PMT jackets will be extruded�

The procedure for assembling the internal components of the MUX boxes includes thefollowing steps

�� The clear optical �bers are cut and trimmed to size� and then inserted and glued intothe connectors�

�� With the aid of the computer controlled LED array� the �bers from the �rst group of�� bers are routed to the �rst cookie in the box and then glued into place�

�� The lacing pattern is tested using the computer controlled LED array�

�� The connectors and cookie are �y cut and polished�

�� The preceding three steps are repeated for the other two cookies in each box�

Prior to installation� PMTs are �t to PMTholders and the assemblies are aligned withthe cookie holders� The PMTs will be installed at the detector sites to reduce any chance ofdamage� Once PMTs are installed� the whole readout chain from the optical inputs at thefront plate to the signal outputs at the electronics is tested� channel by channel using theprogrammable LED array�

��

�� Management �WBS ��

Two of the scintillator system managers are engineers and require salary support for thefraction of time which they spend on management activities� This e�ort is estimated to beone month per year�

Several managers require travel support for regular interactions with the Fermilab management� other MINOS managers and interaction with the collaboration and vendors� Speci�c travel allocations have been made for the scintillator Level � manager and for themodule� assembly equipment and factory managers� In addition� several �generic� trips peryear have been allocated for other members of the scintillator management sta��

�� Future optimization and engineering

�� Purpose and goals

The scintillator system described in this Chapter is a complete design which meets thephysics requirements speci�ed for MINOS� using demonstrated technology and known costs�However� the engineering of the system� including essential largescale prototyping� must becompleted prior to proceeding with production� The baseline design is now at a stage where�ne tuning of components is under way� This �ne tuning is aimed at obtaining the bestpossible light output and at reducing production costs� Some examples of �netuning designchanges we have already adopted are

� Scintillator �uor concentration Our studies have shown that a �� concentration ofPOPOP gives �� to �� more light output than the old baseline of �� POPOP�which had initially been determined from cast samples�� The cost impact of thischange is minimal and is an excellent value for the gain in light output� Large scaleassemblies with strips made with �� POPOP will be built within the next twomonths�

� �Inline� �uor infusion We have recently developed a technique for mixing �uors intopolystyrene as the scintillator strips are extruded rather than in a separate step� It isestimated that the onestep� or �inline� process saves about !�M in the productioncost of scintillator� We note that this single cost savings is more than all the R�Dfunds we have spent on the development of the scintillator system to date�

� Fiber diameter Based on a series of measurements of light collection in our scintillatorwith di�erent �ber diameters� we have decided that �� mm �ber is optimal for MINOS�This maximizes light output and use of the e�ective area of the phototube pixels in theHamamatsu M�� PMT� It is possible that some small additional tuning of the �berdiameter will be optimal for light transmission at connectors�

We note that� during the last year� our ��ne tuning� of the baseline design has resultedin about a factor of two increase in light output� We anticipate that there are additionalimprovements on the order of a few tens of percent to the light output which will be realizedin the next few months of additional �ne tuning� Examples of such work now under way are

��

further studies of scintillator production techniques� optimizing the design of the bulk opticalconnectors� �ne tuning of the thickness of the scintillator� optimizing the manifold design andproduction techniques� and �ne tuning of module design and construction techniques� Anactivity of increasing importance as we head towards production is involvement of industrialsuppliers in the production of our components� We are working with potential industrialsuppliers to ensure that we will have a coste�ective and reliable supply of components formodule assembly�

The schedule for scintillator optimization and engineering is set by the requirement ofhaving modules ready for prompt installation as soon as occupancy in the near and far detector halls permits� We have used the January �� date for occupancy of the far detector hallfor purposes of planning the schedule for scintillator engineering and startup of production�Our schedule includes the following milestone dates

� Nov� �� Lehman Review of baseline design�

� Oct� �� June �� Fine tuning of detector components� Small modi�cationsto the baseline design such as exact �ber diameter �� to �� mm with or withoutsteps at connectors�� thickness of scintillator �� to �� cm�� design of connectors andmanifolds� etc� will be studied and considered for potential cost savings or improvementin light output�

� June �� Review light output and modi�cations to design� Decide all design issues�Start �nal engineering of design�

� Nov� �� Final review and approval of engineering design�

� Dec� �� Place �rst commercial orders for assembly prototype �at Fermilab��

� Jan� � � Start factory setup� Produce modules for assembly tests�

� June � � Place orders for components for �rst supermodule�

� Oct� � � Rampup production of modules for �rst supermodule�

� Dec� � � Two planes of modules at Soudan� ready for installation�

� Mar� � �� Scintillator module production at full rate�

The following activities will be pursued during the engineering and optimization phase

�� Extruded scintillator production We will continue to work with both industrial plasticsextruders and scintillator manufacturers to improve light output and�or decrease thecost for extruded scintillator� Due to the industrial nature of this process� any iterationin the production technique takes a minimum of � months� The optimization includespossible small changes in the geometry of scintillator strips to improve light outputand�or collection�

�� Wavelengthshifting �bers We have found some batch variation in WLS �bers delivered over the last two years� and are working with manufacturers to de�ne testingstandards for long �bers in order to improve their quality control�

��

�� Scintillator module construction Additional work on engineering and prototyping willbe undertaken to ensure understanding of construction issues and to arrive at an optimal design for cost� Full size prototypes are being constructed and tested for lightoutput and mechanical properties� Fullscale planes of scintillator will be assembledon prototype steel octagons and mounted as in the �nal detector to ensure that allintegration issues have been understood�

�� Clear �ber ribbon cables We must establish production of clear �ber cables whichmeet the needs for MINOS� We will arrange orders from Mitsubishi and Kuraray andChinese vendors� An attractive possibility is to have the complete clear�ber assembliesproduced by our IHEP Beijing collaborators�

�� Connectors We are investigating a custombuilt optical connector for MINOS whichis based on designs built for other experiments�

�� Photodetectors The baseline photodetector is the Hamamatsu M�� This device meetsall of the technical requirements of the proposed physics measurements� for the coststated in our baseline documentation�� Our future work with this tube will furtherdevelop our understanding of tubetotube variations in response� in parallel with testing of improved versions of the tube which Hamamatsu is continuously developing� Wehave performed considerable R�D work to compare the possibility of using an HPD�hybrid photodiode� rather than the M�� PMT� The use of an HPD o�ers some potential advantages compared to the PMT due to various technical di�erences� includingbetter intrinsic stability and uniformity of HPD photon response compared to PMTs�We have not identi�ed any su�ciently large advantage of the HPD for MINOS whichwould justify changing our baseline design� Some work continues on study of the HPDas a possible design contingency to the baseline�

�� Calibration A complete calibration system has been described for MINOS� basedon experience and speci�c designs used in previous calorimeters� However� there areseveral aspects of deployment in MINOS where further reductions in cost are possiblewith additional optimization work�

�� Aging tests Most detectors built with solid scintillator display a mild drop in lightoutput as a function of time due to yellowing and other aging e�ects� The light outputof the MINOS baseline design is high enough that the sensitivity of physics measurements will not be degraded by such e�ects� Although the MINOS scintillator designincorporates a number of features which have not been used in earlier experiments�all of the components of our scintillator modules have been used in previous detectorswith no signi�cant problems due to aging� However� we must ensure that new featuresof the MINOS application do not introduce an unacceptable rate of decrease in lightoutput versus time� We have already begun a program of aging tests to demonstratethe longterm stability of all of our components and assemblies�

�� Fullplane prototypes In order to understand system integration issues we will assemble a series of fullsize prototype planes of scintillator� mounted on steel octagons�

��

and will study these with calibration systems and cosmic rays as part of the �planeprototype studies in the New Muon Lab at Fermilab �see Sections �� and ��

�� Test beams studies In order to ensure that the full system works as expected� testbeam measurements of hadron calorimetric response will be made �see Section ��

�� Aging tests

Long term e�ects of various stresses on the scintillator strip assemblies are being studied�The aging tests are planned to continue for the next several years to quantify the e�ects ofaging� We have placed �bers� scintillator strips� glue samples and full scintillator��ber�glueassemblies in several aging conditions including

� High temperature ��C��

� Cycled temperature ��C to "��C every � hours��

� High temperature " high humidity ��C and �� relative humidity��

� Mechanical stress �assembled strips bend around a �� m radius��

The main e�ects have been observed in high temperature and for �bers high humidity aswell� Aging in the glue has a negligible e�ect �due to the thin layers which will be used inMINOS�� Aging in both the scintillator and �bers contributes to a slow drop in light outputat high temperature� In � months of aging at ��C we have observed a drop in light outputof about �� to �� in complete assemblies� The expected acceleration factor is around ��or more� so that this corresponds to about �� months of aging at normal temperature� Wehave concluded that we can expect less than a factor of two drop in light output over aperiod of ten years�

�� Test beam studies

Should signatures of neutrino oscillations be observed in MINOS� it will be of interest toreduce all systematic errors as much as possible in order to get the best precision in oscillationparameters� In this case� it will be of interest to undertake an expanded e�ort on test beammeasurements beyond that described in Section �� We anticipate that with such ane�ort� the systematic uncertainty in the absolute energy scale in the near and far detectorscould be reduced to less than �� In addition� more detailed information on the topologyof showering events in the detector could be obtained� The plan is that the calibrationmodule will be built from modules with connectors identical to those used in the near andfar detectors� By simply purchasing additional photodetectors and electronics� it will bepossible to instrument the calibration module with the full transverse granularity as in thenear and far detectors� This would also help to check for any systematic e�ects which mightarise due to di�erences in summing of signals between the initial calibration module and thenear and far detectors�

In addition to the extra instrumentation� the calibration module could also be magnetizedin order to provide a direct measurement of the change in response in this condition� Previous

��

measurements have shown that the response of hadronic showers can change when the iron ismagnetized�� To �rst order� the change can be corrected without a direct measurement�

Finally� it will be possible to move the calibration module to the near and far detectorsites� In both locations� data from cosmic ray muons could be collected and compared toensure a complete understanding of the energy deposition at the two sites� In addition�neutrino events could be measured at the near site and compared to those observed in thenear detector target�calorimeter region�

Chapter � References

�� Detailed costs and schedules corresponding to the design described in this Chapter aregiven by the Fermilab NuMI Project Sta� in �NuMI Project Cost and Schedule Plan��October �� Fermilab report NuMI��

�� M� Adams et al�� Nucl� Instr� Meth� A��

�� M� Adams et al�� Nucl� Instr� Meth� A��

�� Kuraray Co�� Methacrylic Resin Division� �F� Maruzen Building� �� Chome� Hihonbashi� Chuoku� Tokyo� �� Japan� Kuraray America Inc�� Park Avenue� NewYork� NY ��

�� Quick Plastics� �� Wayland Dr�� Jackson� MI ��

�� Polycast and Royalite are divisions of Uniroyal� Royalite Thermoplastics �� W� Washington St�� P�O� Box �� South Bend� IN �� Polycast Technology Corporation� ��Carlisle Place� Stamford� CT ��

�� Dow Chemical Company� �� Dow Center� Midland� MI ��

�� Chroma Corporation� �� Dayton St�� McHenry� IL ��

�� Bicron Corp�� Kinsman Road� Newbury� Ohio ��

�� G� Apollinari� P� de Barbaro and M� Mishina� �CDF End Plug Calorimeter UpgradeProject�� FermilabConf��E� CDF note ��

�� M� Chung and S� Margulies� �Aging studies on stressed and unstressed scintillating�waveshifting and clear �bers�� Proceedings of SPIE ��

�� Epon is a trade name for Epoxy resin manufactured by Shell�

�� Manho Chung� University of Illinois� Chicago� DO Collaboration� private communication�

��

�� Hamamatsu Photonics K�K�� Sunayamacho� Hamamatsu City� �� Japan� U�S�Main O�ce �� Foothill Road� P�O� BOX �� Bridgewater� NJ ��

�� The HERAB experiment at DESY is designed to study B meson decays produced by�� GeV protons striking an internal thin wire target� Two types of photomultipliers areemployed by HERAB ring imaging Cerenkov counter Hamamatsu R��U��M�� andM�� There are �� M�� tubes and �� M� tubes used�

�� CDF collaboration� The CDF II Detector� Technical Design Report� November ��

�� J� Bahr et al�� Nucl� Instr� Meth� A�� G� Apollinari et al�� Nucl� Instr� Meth� A�� Yu� Bonushkin et al�� Nucl� Instr� Meth� A�� M� Lindgren et al�� Nucl� Instr� Meth� A��

�� DDK electronics� �� Oakmead Village Dr�� Santa Clara� CA ��

�� S� Kasahara� Ph�D� thesis� U� Minn ��K� Ruddick� �Underground particle �uxes in the Soudan mine�� NuMIL��R�K� Menon and R� Murthy� Prog� Elem� Part� and C�R� Phys��

�� S� Kunori� �BField e�ects on scintillator and calorimetry�� VII International Conferenceon Calorimetry in High Energy Physics� Nov� �� Tucson� AZ�

�� V�V� Abramov� Nucl� Instr� Meth� A��

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Chapter 5 Scintillator detector fabrication

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Transcript of Chapter 5 Scintillator detector fabrication