November 30, December 1, 2006 MSL RAD Sensor Head (RSH) peer review 03 – RAD Sensor Head (RSH)...

November 30, December 1, 2006MSL RAD Sensor Head (RSH) peer review

03 – RAD Sensor Head (RSH) Overview

RAD – The Radiation Assessment Detector for MSL

Wimmer-Schweingruber1

DLR

03 – RAD Sensor Head (RSH) Functional Overview

Robert F. Wimmer-Schweingruber, IEAP/CAU, Kiel, Germany

RAD Packaging Review





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RAD Level 2 Science Requirements

RAD Science Requirements:

•RAD shall measure energetic charged particles (Z=1-26) with energies up to 100 MeV/nucleon.

•RAD shall measure neutral particles (neutrons and gamma-rays) with energies up to 100 MeV

•RAD shall measure energetic electrons with energies up to 10 MeV.

•RAD shall measure dose and LET spectra on the Martian surface.





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• RAD shall measure energetic particles with an energy resolution sufficient to distinguish between major particle species (i.e. protons, He), low Z(i.e. p, He, Li ions), medium Z(i.e. C, N, O ions), and high Z (i.e. heavier nuclei up to Fe) particles.

• RAD shall measure energetic particles with time resolution sufficient to obtain time series observations over the course of the MSL baseline mission and to resolve spectra associated with solar particle events when they occur.

RAD Level 2 Science Requirements (cont’d)





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Charged Particle Interaction with Matter

• Ionization• electron content important• heavy ions deliver more dE/dx

dE/dx ~ Zp

2 /E...





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Summary of Measurement Requirements

A

CB

F

G

E

D

n

g

ion, electron• Charged particles (Z = 1–26)

up to 100 MeV/nuc

• Neutral particles (n, )

up to 100 MeV/nuc

• Electrons up to 10 MeV

• LET

• Species discrimination

• Time series

• Autonomous operation





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RAD Sensor Head (RSH)n-Measurement Principle

Thus need transparent high-proton-content material

neutronscattered

recoilprotonneutron Charged proton

is easy to detectby induced scintillation.

E recoil

q90ﾰ0ﾰ

q

log s

log E [MeV]1 10

[barn]

1

105





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n-Measurement Approach

Neutron Channel:

Conversion of neutrons to detectable protons using 30 g of high proton-content-scintillator (BC432(m))

Neutral particle detection requires efficient anti coincidence (AC)

MIPs energy deposit 2 MeV/g/cm2

→ use 12mm BC432(m)

Need ≥ 99.8 % efficiency,

no crosstalk, light tightness





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n-Measurement Approach

Don't want high voltage in Martian atmosphere.

→ Read out light signal with PIN diodes.

Use same detectors as for charged-particle telescope.

→ Resolve very

small signal.

→ Need good

CSAs.

background

muon signal





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g-Measurement Principles

Thus need transparent high-density material

Photo-effectCompton effect

Pair production





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g-Measurement Implementation

MSL RAD CsI- crystal

CsI is a very efficient gdetector, moreover, 30 mm CsI stops 100 MeV protons and 200 MeV/nuc iron. Signal read out with PIN diodes.

Test diode(non flight)





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n-g-Measurement Implementation

Keep CsI calorimeter (D) and

n-channel (E) close together and

inside telescopoe FOV for charged

particle measurements.

Stack must be inside efficient AC.

nSeparation of n and gby statistical method similar to a method also applied to SOHO data (Böhm et al., 2006)

gD

E





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Statistical Separation of n and g-rays by Matrix Inversion





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Measurement Implementation

Solar particle event measurement

requires maximization of geometric

factor:

FoV

Active Area

Particle discrimination FOV half-angle q60°

Simulations and other considerations:

q = 32.5 deg. Results in acceptable path-length variations.

CsI thickness 28 mm results in 100 MeV/nuc stopping power for most particles.

q





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RSH SSD Geometry

• Three SSDs allow limited dE/dx

• close gaps in anti-coincidence A

BC

D

EF

B

C

D

F





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**The RTG will induce a background to the neutron and g-ray channels, which will be characterized during cruise phase for improved background subtraction.

r a d ia t ion coun t r a te unce r ta in ty m ode l unce r ta in ty(pa r t ic le ) [%/6 m on ths ] (dos im e tr y)p 0 .25 0 .1 20%e 0 .02 0 .35 20%CN O 0.7 20%F e 3 20%n 20 - 200 0 .25 – 0 .75 100%dos im e tr y 25 0 .7 (pe r hou r ) -

[s -1]

5x10 -3

3x10 -4

*SPE count rates will be 10 – 1000x greater depending upon the flux and spectrum of the event.

Expected RAD Count Rates (GCR only)





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RAD Performance: RTG background

Tl-208

2.614 MeV

Pu-238

0.766 MeV

S.E.

2.103 MeV

D.E.

1.592 MeV

Pu-238

0.154 MeV





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RAD RSH Measurement Requirements Summary

Re q u ire m e n t s ta tu s p la n sc: PF , E Mt ,c: PF , E M

s,h (SOH O, Ulysse s ) c: PF , E MLE T c: PF , E Mspe cie s d iscr im ina t ion s ,h (SOH O) c: PF , E Mt im e se r ie s s ,h (SOH O) c: PF , E M

Cha rg e d p a r t ic le s< 10 0 M e V/n uc s ,h , t w . cosm . m u on sne u t r a l pa r t ic le s < 1 00 M e V/nuc s ,h (N e udos), te le ct ron s E < 10 M e V

s,h (Dos t e l/ISS)

c: calibration, h: heritage, s: simulation, t: tests

Requirements and Expected Performance





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RSH Model philosophy

• Pathfinder unit built flight-like, but no qualification standard. For CAU-internal testing and process development purposes only.

• Engineering model: flight-quality model, qualification unit for all RSH qualification tests.

• Flight model: test only to acceptance level.

• Flight spare: same standards as flight model, use for full calibration (refurbished engineering model is currently only carried as a backup option)





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RSH Overview Summary

•CsI energy/thermal response characterized•RSH modelling ongoing and assuring•Manufacturing ongoing•Pathfinder SSD delivery imminent •Flight SSD bonding to wait for Pathfinder•Thermal test chamber delivered•2 diploma theses completed





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Backup Slides





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RAD Sensor Head Overview

Institute for Experimental and Applied Physics (IEAP), Kiel University

Experience:• Helios, ISEE-2, Galileo, Ulysses, SOHO, STEREO• Dostel (ISS), Matroshka, EUTEFFacilities:• fully equipped machine shop, electronics shop• calibration facilitiesFunding:• Deutsches Zentrum für Luft- und Raumfahrt (DLR) (to 12/09)• German Science Foundation (DFG)Personnel:• experienced (state-funded) personnel in group (9) and machine shop (13) plus project-funded scientists and engineers





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RAD Science Requirements





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GCR Interactions with the Atmosphere

• Secondary production• Energy input





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Planetocosmics:A GEANT 4 application for tracking particles in the

vicinity of a planet

particle propagation through the Planets atmosphere

Visualization of tracks incl. production of secondaries

Calculation of the energy depositions

Calculation of the fluxes of secondaries, e.g. neutrons

Calculation also in the presence of relic crustal magnetic field





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Preliminary Simulations

Pfotzer Maximum atEarth is at about 20 km

Pfotzer Maximum on Mars is at surface level





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n-Measurement Implementation

MIPs deposit very little energy in anti-coincidence.

Therefore, to reach high A/C efficiency,we need to understand:

• peak shape• background• energy deposit

Measured pure cosmic muon signal in BC-430 anti-

coincidence (A/C) material.low energy deposit

insert energy





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Background in detectors results in partial hiding of MIPS signal.

background

muon signal

High-efficiencyA/C triggeringon MIPs requires running into background toget all MIPs.





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measured efficiency curve

“100%” efficiencyat low E-channels

99.8% anticoincidence efficiency demonstrated





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• RAD single detector count rates (estimation)

inner 2 segments45 counts/s7 counts/s60 keVPIN Photo-diode C

300 µm, 2.3 cm2

middle segment, anti-coinc.30 counts/s5 counts/s60 keVPIN Photo-diode C

300 µm, 1.5 cm2

outer 3 segments with BC430 cylinder

190 counts/s +

205 counts/s

30 counts/s +

2 counts/s

60 keVPIN Photo-diode C

300 µm, 10.1 cm2

inner segment35 counts/s6 counts/s60 keVPIN Photo-diode B

300 µm, 1.9 cm2

inner 2 segments45 counts/s7 counts/s60 keVPIN Photo-diode A

300 µm, 2.3 cm2

outer 4 segments, anti-coinc.210 counts/s35 counts/s60 keVPIN Photo-diode A

300 µm, 11.6 cm2

RemarkWith RPSWithout RPSThresholdDetector





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• RAD single detector counting rates (estimation, continued)

worst case area

40.0 cm2

205 counts/s **2 counts/s **150 Nphoto-electronsBC430 Cylinder, anti-c.

50 mm high

worst case area

66.5 cm2

340 counts/s2 counts/s150 Nphoto-electronsBC430 Scintillator F

12 mm high

worst case area

20.4 cm2

105 counts/s1 counts/s150 Nphoto-electronsBC430 Scintillator E

18 mm high

worst case area

10.6 cm2

190 counts/s1 counts/s40 Nphoto-electrons*CsI Scintillator D

28 mm high

RemarkWith RPSWithout RPSThresholdDetector

* Threshold does not drive the design, somewhat arbitrary

** Counted in detector C (outer 3 segments)

November 30, December 1, 2006 MSL RAD Sensor Head (RSH) peer review 03 – RAD Sensor Head (RSH)...

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