Emulsion Detectors

University of BERN Albert Einstein Centre for Fundamental Physics LHEP M.Fatih BAY

TextBooks for Emulsion Detector

• Nuclear Research Emulsions. Vol.1: Techniques and Theory Barkas, Walter H.

(Pure and Applied Physics, New York: Academic Press, 1963Walter) • Nuclear Research Emulsions. Vol.2: Particle Behavior and Emulsion

Applications. Barkas, Walter H.

• The study of Elementary Particles by The Photographic Method: C. F. Powell, P. H. Fowler and D. H. Perkins, (Pergamon Press, 1959. xvi–669 p. £12 10s.)

OUTLINE

• A Video of Pion Interaction inside Nuclear Emulsion

• Nuclear Emulsion.

• Physical and Chemical Constitution of Nuclear-Track Emulsions.

• History of Nuclear Emulsion.

• Emulsion Read-Out System.

• Modern Techniques of Nuclear Emulsion and their application..

Pion Interaction inside Emulsion Detector

• Nuclear emulsion is a three-dimensional tracking detector for charged particles having a spatial resolution of less than 1 μm

~120 Micron

What is Nuclear Emulsion in Particleand Nuclear Physics?

• Nuclear Emulsion particle detectors feature the highest position and angular resolution in the measurement of tracks of ionizing particles.

• Nuclear Emulsion, used to record the tracks of charged particles, is a photographic plate.

• A photographic emulsion consists of a large number of small crystals of silver halide, mostly bromide.

• The sensitivity to light has allowed silver halides to become the basis of modern photographic materials.

Nuclear Disintegration

What is Nuclear Emulsion?(2)

• A silver halide is one of the compounds formed between silver and one of the halogens — silver bromide (AgBr), chloride (AgCl), iodide (AgI), and three forms of silver fluorides.

• The method of recording tracks of charged particles in photographic plates is based upon two achievements of modern technology, the photographic emulsion and the optical microscopes. Pion Interaction

The Latent Image

• A latent image on photographic film is an invisible image produced by the exposure of the film to light.

• The arrangement of atoms in a perfect silver-halide crystal is equivalent to face-centered cubic lattices.

• The lattice is commonly not perfect. It contains dislocations which are important in promoting the growth of the crystal from the solution.

Latent Image Formation• The absorption of energy in a

sensitized crystal of silver bromide leads to a concentration of a few silver atoms of the sensitizing layer, initially dispersed over the surface, into an aggregate which can act as a development centre, i.e. a Latent Image

By Fuji Film Electron micrograph of Silver Halide Crystals

The Development• Photographic developer is a chemical amplifier

acting on the latent image.

• A rather complex physics-chemical process is able to transform those grains with a suitable development centre into metallic silver.

• After development, a silver halide emulsion is placed in a second bath, called as fixer which dissolves the unaffected grains of silver halide but leaves the small black granules of silver.

• Finally, The plate is washed and dried.

Emulsion Films drying after development

The Mechanism of Development

by Fuji Film

The Silver Halide Grains (linear size of 0.2 micron)

the track left by a minimum ionizing particle in nuclearEmulsion. About 35 grains/100 micron

Latent Images

Summary of Whole Process

Refresh

The Role of the Gelatine

• The Gelatine provides a three dimensional net-work which serves to locate the small crystals of the halide and to prevent them migrating during development and fixation.

• It is able to absorb large quantities of water.

• The gelatine molecules are adsorbed to the ions in the surface of the halide, so that the grains are held fixed, like flies on a spider’s web.

• The gelatine also contributes to the sensitivity of the silver halide grains.

Nuclear Emulsion vs. Photographic Films

• Nuclear Emulsion differs from those of ordinary photography in three respects.

1. The ratio of silver halide to gelatine is about eight times larger in the nuclear emulsion.

2. The emulsion is commonly between ten and a hundred times thicker.

3. Developed silver grains are smaller and more uniform.

Fuji Nuclear Emulsion Film

• The development of the scanning system requires

good quality emulsion plates.

• Two layers are separated by a protection coat

(thickness of 1 micron).

• R&D project was jointly being carried out by Nagoya

University and the Fuji Photo Film Co., Ltd

Emulsion Refreshing (Memory Reset)

• A procedure to erase to a large extent any previously recorded background due to latent image tracks produced by ionization.

• Emulsion refreshing is obtained by keeping the films at high humidity (95-99% RH) and high temperature (25-30◦ C) for a few days

Refreshing Apparatus

Emulsion Refreshing(2)

Scanning was done by the UTS automated scanning system at the Nagoya University

Discovery of Radioactivity• The first notable the use of the photographic emulsion(plates) is

the discovery of radioactivity by Henri Becquerel in 1896.

• The radiation emitted by uranium shared certain characteristics with X-rays but, unlike X-rays, could be deflected by a magnetic field and therefore must consist of charged particles. For his discovery of radioactivity, He was awarded the 1903 Nobel Prize for physics.

Measurement of α-Particles• S.Kinoshita found record of alpha-particle

radiation detected as tracks by means of optical microscopes.(in 1910)

Experimental Apparatus.

Tracks Produced by Cosmic-Rays

• The Balloon, Explorer II in 1935, was the first attempt to employ photographic method to detect tracks due to cosmic radiation. (73.000ft for more than two hours.)

• The balloon carried photographic plates for Rumbaugh and Locher (1936) who found no tracks in their plates and for Wilkins and Helens who found of long tracks some of which appeared to be involved in nuclear collissions (1936,1938).

• Long tracks of Protons were also observed by Tokio Takeuki (1937).

Discovery of Heavy Mesons• The Emulsion technique greatly improved

during 30’s and 40’s thanks to the group of the Bristol University lead by POWELL.

• Developing of electron sensitive Nuclear Emulsions.(Produced by ILFORD and KODAK)

• In parallel, dedicated microscopes were developed.

• The Cosmic-Ray Pion was detected through its decay into muon.(by Powell)

• Powell was awarded the Nobel Prize for physics in 1950 for his discovery using nuclear emulsion.

Cecil Frank Powell

The contributions to Discovery of Elementary Particles

The Discovery of new particles by using Nuclear Emulsions

• In 1947, π+and π- were discovered by Powell.

• In 1947, K+and K- were discovered.

• In 1953, Σ+ was discovered by A. Bonetti.

• In 1958, Anti Λ0 was discovered by Baldo Ceolin.

• In 2001, ντ was discovered by DONut collabration.

Particle Instrumentπ+ and π- Nuclear Emulsion

π0 Counters and Emulsion

Λ Cloud Chamber

K+and K- Nuclear Emulsion

K0 Cloud Chamber

Σ+ Nuclear Emulsion

Σ- Cloud Chamber

Σ0 Bubble chamber

Ξ- Cloud Chamber

Ξ0 Buble Chamber

Anti Λ0 Nuclear Emulsion

The Discovery of new particles by using Various Detectors

Emulsion Cloud Chamber(ECC) Detectors

• A major breakthrough in the emulsion technique was the introduction of the ECC.

• The ECC technique was first introduced in 1951 by Kaplon to study heavy primaries in cosmic ray interactions.

• Sandwiching emulsion films with passive material layers, usually made of plastic, metal or lead plates.

• Spatial resolutions down to 1 micron with 3D Capabilities, reconstruction of the cascade showers in the Detector.

• ECC detectors were first applied to the study of the cosmic-ray spectrum and to very-high energy interaction process.

A Schematic Structure of ECC.

A Reconstructed νμ CC Event inside ECC.

Nuclear Emulsion Applications• Medical Application with Nuclear Emulsions(Proton Radiography).• Emulsion Hybrid Telescope for Cosmic Gamma-Ray Observation.• Cosmic-Ray Muon Radiography of Volcanos with ECC.• Radiation Monitoring around Accelerator.• The Detection of Dark Matter.• Application to Neutrino Experiments.• Muon Monitoring at Muon Pit at J-PARC.• Electron/Pion Separation.• OPERA Experiment.

Particles for Medical Application

• Proton therapy : very high local control of the pathology with minimal secondary effects.

• A particle accelerator is used to target the tumor with a beam of protons.

• The dose delivered to tissue is maximum just over the last few millimeters of the particle’s range; this maximum is called the Bragg peak

• To treat tumors at greater depths, a beam with higher energy.

Proton Radiography with Nuclear Emulsions at LHEP

• To obtain medical images of the patient’s body (proton radiography).

• Proton radiography allows obtaining images directly proportional to the average density of the traversed material.

• Emulsion detector is cheaper and easier to install and remove.

Emulsion Hybrid Telescope for Cosmic Gamma-Ray Observation.

• Telescope observes

1.Brightness (Magnitute)2.Color (Wavelength)3.Direction of the light

• Emulsion Measures

1.Event Rate (Flux)2.Energy (Momentum)3.Direction of gamma-ray

photon

Visible (Palomar)

2 mrad

Ultra Violet (UIT) Reconstructed

Tracks Gamma Shower

Cosmic-Ray Muon Radiography of Volcanos with ECC.

muon

ECC

• Muon source with a well-known energy spectrum for different zenith angles.

• A well-understood muon detector.

• The information from counting muon events at different arriving angles can be used to infer on the matter profile.

Cosmic-Ray Muon Radiography of Volcanos with ECC.

pg

Cosmic-Ray Muon Radiography of Volcanos with ECC.

Result in USU

π

μ

e

The PEP4/9-TPC energy deposit measurements

The Bethe-Bloch Formula

Particle Identification.

• In Emulsions, the grain density is proportional to energy loss by ionization(Bethe-Bloch)

• If the momentum known, dE/dx allows the particle identification.

• If the Momentum unknown, the combined measurement of momentum(βP by MCS) and grain density allows particle identification.

β2=p2/(p2+m2)

Bethe-Bloch for Different Materials

Horizontal Exposure

Two modules (5cmx5cm) were prepared, each module has 2 OPERA films inside.

They were exposed horizontally at different angles and at different momentums

(500MeV/c, 1 GeV/c, 1.5 GeV/c,, 2GeV)/c, ~104/cm2

Developed at CERN.

0.5GeV/c

1.5G

eV/c

1G

eV

/c2GeV/c

Prepared And Exposed at CERN

Grain Counting

-Tracks are selected as depending on angle. -Track Grains are counted unit by unit.-Unit length not yet calibrated.-Pion Tracks are found by looking pion interactions

Results and Discussion

• The results fit perfectly with theory.• OPERA Films allow to separate at low momentum of particles.

The OPERA Experiment

• Mainly designed for the direct search of ντ appearance in the pure νµ CNGS beam from CERN to Gran Sasso(732km).

• Based on the use of Emulsion Cloud Chambers (ECCs) and of electronic detectors(Hybrid Detector).

• In an ECC the nuclear emulsion films act as very high precision tracking detectors, and are interleaved with plates of lead.

• The brick, is made of 57 emulsion films interleaved with 56 lead foils of 1 mm thickness. It has 128x102x79mm3, and weighs 8.3 kg.Emulsion Cloud Chamber

The OPERA Experiment• The distinctive feature of ντ charged-current

interactions is the production of a short-lived τ lepton (cτ =87 µm).

• This is achieved in OPERA using the Nuclear Emulsion technique that features an unrivaled spatial resolution (≤ 1 µm).

• OPERA Detector is a hybrid (emulsion+electronics) with a modular structure.

2 SuperModules=2*(31walls+1spectrometer) Total Mass: 1766 Tons. # of Bricks=206336

• ECC measures: Kink of Tau, Momentum(via MCS), Electromagnetic Shower, dE/dX, e/π separation, Event Kinematics,Vertex Location, τ ID,

• Magnetic Spectrometer: μ ID, charge and momentum.Target tracker: Trigger and localiza ν interactions.

Electromagnetic shower reconstruction

The OPERA Experiment

• The required area of emulsion is of order of 100,000 m2 s

• It is needed high-speed automatic scanning systems.

• Scanning power is 10cm2/h at LHEP

• Emulsions are scanned at Europe and Japanese scanning Labs.

Hybrid Detectors(Emulsion+Electronic Detectors)

• Hybrid experiments combining ECC and Electronic detectors.

• To provide time resolution to the emulsion stack (trigger signal).

• To pre-select the region of interest for the event occuring in the ECC.

• The ECC is removed from the detector for reconstruction and analysis of the events.

Emulsion Cloud Chamber

Changeable Sheets (CS) Detectors

• Used as interfaces between Target Tracker detectors and Emulsion Cloud Chambers.

• They are placed to the downstream face of the ECC.

• It confirms neutrino interaction signals obtained from TT detector.

• To find neutrino-related interactions for the ECC brick.

• To decrease useless scanning load, useless film handling and processing

Automated Emulsion Read-out System

• The first microscopes to scan emulsion detectors were Human-eye based. (difficult to increase speed for data acquisition)

• The first automated scanning system wasTrack Selector(TS) developed by Nagoya University in 1974 (Invented by K.Niwa)

• Japanese and European groups have separately developed new automatic high-speed scanning systems.(Super-Ultra Track Selector,S-UTS and European Scanning System ESS)

Digitizing Grains inside Emulsion

• The images are collected at different gray levels.

• The micro-tracks are reconstructed

• Base-tracks and Volume tracks are reconstructed for event analysis.

Film base　 200-800 mm

MicroscopeZ-axis

Objective lens : 50x　~3mm DOF (effective)

Resolution : 　　　　　　　　512x512 pixelsFOV　 :　 160x160mm2

Eff. Pixel size　 : ~0.3mm　

Emulsion （ backside)　

Nucl

ear

em

uls

ion fi

lm

Imagesensor

Imagesensor

Emulsion (topside)typ. 45-100 mm

LHEP Emulsion Scanning LAB. At University of BERN.

Data Acquisition and Plate Changer System developed by I.Kreslo