scintillation detectors for space radiation and dosimetry -
TRANSCRIPT
August 2012
1
Scintillation Detectors for Space Radiation and Dosimetry Goal: Neutron Dosimeter
James Christian
Instrument Research& Development
E.B. Johnson, C.M. Whitney, X.J. Chen, S.M. Vogel, E.V.D. van Loef, R. Hawrami, J.Glodo, L.S. Pandian, K.S. Shah, T.H. Prettyman, E. Benton
SBIR
PSI OSU
2
Compact Dosimeter Concept
• Scintillation detector and SSPM • Simplistic
– Anti-coincidence (distinguished ions from n, γ) • Scintillation material capabilities
Radiation
Optical Flash
Scintillation Material
SSPM
IC Components Dosimeter Chip
• Neutron dose (2°) important, lots of “stuff”
3
Dose • Absorbed dose (TID) • Human-equivalent dose: Tissue and Q (quality factor)
– Q: “legislated” relative biological effectiveness (RBE) for cancer endpoint: depends on E and LET
• Displacement Damage Dose (NIEL – non-ion. E loss)
• Identify Particle Type • Linear Energy Transfer (LET = ) or E • (Dose rate)
Deq = RBE × DR → Specific
10-4 10-3 10-2 10-1 100 101 102 103
Particle Energy (MeV)
10-6
10-5
10-4
10-3
10-2
10-1
100
101
Si N
IEL
(MeV
cm2 /g
)
ProtonElectronNeutron
*Td = 21 eV
Si
S. Messenger, SPENVIS Workshop 2005
BLAKELY, E.A., et al., Adv. Radiat. Biol. 11 (1984) 195–389.
ICRP 60 (1991a)
dEdx
4
Interactions with HnCm Scintillator
• DPA is a “new” H18C26 material (~tissue density) • Light ∝ Absorbed Dose TID: Birks legacy (S & kB quenching) • Recoil proton (in plastic) related to neutron energy
p+ n γ
p+ (in plastic)
δ-rays
CH
CH3
CH2
n
PVT (EJ200) DPA
2
dEdL dxdx dE dE1
dx dx
S
kB C
⋅ =
+ ⋅ − ⋅
5
Proportionality with gammas: S-term
• S-term related to gamma ray energy resolution • ~15 k photons per MeV (bright – as high as 20)
0 200 400 6000.0
0.5
1.0
Rela
tive
Ligh
t Yie
ld
Energy (keV)
EJ200: ~9 phot/keV DPA: ~15 phot/keV
6
Characterize kB-term (protons) dEdx
• kB larger in DPA than EJ200 (C-term fixed) – More δ-ray/ionization quenching – Deviation not analysis (Experimental factors)
0 5 10 15 200
5
10
15
20
52MeV70
MeV
DPA
kB 0.011 cm/MeVC 7.9E-6 (cm/MeV)2
∆L
/∆x/
S (M
eV/c
m)
⟨dE/dx⟩ (MeV/cm)
EJ200
kB 0.026 cm/MeVC 6.4E-6 (cm/MeV)2
187MeV
50 100 150 20001234567
kB 0.026 0.011 cm/MeVC 6.4E-6 7.9E-6 (cm/MeV)2
L/S
(MeV
)
Ein (MeV)
0.5 cm DPA Fit 0.3 cm EJ200 Calculated
DPA EJ200
2
dEdx
dE dE1dx dx
i
i
i i
S
kB C
⋅
+ ⋅ + ⋅
∑
Sum
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DPA emission time characteristics
• Distinguishes gammas from neutrons
0 200 400 600 800 1000
10-3
10-2
10-1
100
T ~ 25C
DPA #2
R6233SBA(2) / 1100 V / CAEN
neutron gamma windows
coun
ts, a
rb. u
nits
time, ns
window 1 window 2
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DPA neutron distinction
• Different sources • Dark noise • Effect of DDD
0 10 20 30 40 50 60 70 80
0.0
2.0x10-4
4.0x10-4
6.0x10-4
8.0x10-4
dark
cur
rent
(A)
time (days)
30 V reverse bias
10 rad100 rad
1 krad
10 krad
100 krad
PMT (Cf) SSPM (AmBe)
w2/
w1
Neutrons
Gamma (w2-
w1)
/ttl
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DPA population plot
• Ideal beam measurement - Optimistic (avg. paths) • DPA needs anti-coincidence
increasing LET
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CLYC Scintillator Cs2LiYCl6
• Photon yield ~20 photons/keV • CLYC proportional (good gamma E-resolution)
6Li: 6Li + 1n → 3H + 4α 4.78 MeV 940 Barns 35Cl: 35Cl + 1n → 35S 0.62 MeV <1 Barn
10 100 1000
0.90
0.95
1.00
1.05
1.10
1.15 CLYC NaI(Tl)
rela
tive
light
yie
ld
energy, keV0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.50
1
2
3AmBe spectrum
137Cs spectrum662 keV
3.4 MeV
inte
nsity
, arb
. uni
tsenergy, MeV
0 200 400 600 8000.0
0.5
1.0
1.5 CLYC : ∆E ~ 3.9% NaI(Tl) : ∆E ~ 7%
137Cs Spectra
inte
nsity
, arb
. uni
ts
energy, keV
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CLYC emission time characteristics
• Distinguish gammas from thermal neutrons (3-He) • No p+ recoil, detect fast neutrons with 35-Cl
0 200 400 6000.0
0.2
0.4
0.6
0.8
1.0
1.2
gamma
neutron
window 2window 1
neutron gamma windows
coun
ts, a
rb. u
nits
time, ns
100 200 300 400 500100
200
300
400
500
CLYC:Ce
gammas
neutrons
wind
ow 2
/ wi
ndow
1
0 100 200 300 400 5000
10k
20k
30k
40k
neut
ron
2614
keV
511
keV
1274
keV
coun
tsfull integral
100 101 102 103
neutrons
gammas
FOM=4.82
counts
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Measuring neutron energy with CLYC
200 400 600 800 1000 0 100 200 300 400 500 600
Channel
Counts
893 keV 1202 keV 1508 keV 1913 keV
0 500 1000 1500 2000 0 200 400 600
Energy (keV)
Channel
• 35-Cl (n,p) reaction • Fast Neutron Spectroscopy
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Summary
• Interesting Scintillation Materials – Thermal and fast neutron – Distinguish p+, n, & γ – Beam results optimistic
• Compact Neutron Dosimeters and Spectrometers – Anti-coincident shield – Pulse-shape discrimination (electronics) – SSPM detectors: compact, high gain
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Achievements Tested CLLBC Dosimeters at PNNL:
• Category 1 – isotopes passed, x-ray failed • Category 2 – isotopes passed, x-ray “close”
Designed Category-1 x-ray detector Received and tested new dosimeter chip Designed new compact version Developing HDD, SDD, assembly,
testing, and QC protocols: ISO 9001 compliance
Facilities: Constructed x-ray room, crystal preparation station, dry glove box, environmental chamber automation.
Met with Stan Mavrogianis and Eric Daxon at HPS meeting
-0.2 0.0 0.20.0
0.2
0.4
2b
2c
1
Devia
tion
Bias
ANSI Category (corrected)
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Space Environment
• Neutron dose important, lots of background
10-3 10-2 10-1 1 10 102 103 10410-610-510-410-310-210-1
110
102
Parti
cles/
(cm
2 ·s·M
eV)
Energy (MeV)
Gamma Neutron Proton
• Galactic Cosmic Rays (GCR), Solar Protons and Secondary Emission (gamma-rays, neutrons, and others)
p+ (GCR) p+
nγ
δRδR
Simulation