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

7

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

8

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

9

DPA population plot

• Ideal beam measurement - Optimistic (avg. paths) • DPA needs anti-coincidence

increasing LET

10

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

11

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

12

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

14

15

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)

16

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