scintillator materials for gamma ray spectroscopy cherepy forexternal

Lawrence Livermore National Laboratory

N.J. Cherepy, [email protected]. Payne, B.W. Sturm, J.D. Kuntz, Z.M. Seeley, B.L. Rupert, R.D. Sanner,

T.A. Hurst, P. Thelin, S.E. Fisher, O.B. Drury

Lawrence Livermore National Laboratory, Livermore, CA 94550

K.S. Shah and team, Radiation Monitoring Devices

A. Burger and team, Fisk University

L.A. Boatner and team, Oak Ridge National Laboratory

Scintillator Materials for

Gamma Ray Spectroscopy February 2011

LLNL-PRES-468519

This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344

Funded by DHS/DNDO

and DOE NA-22

mailto:[email protected]

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Official Use Only

N. CHEREPY [email protected]. CHEREPY [email protected]

Requirements for new detector materials:1) High energy resolution and stopping — to discriminate gamma spectra

2) Low cost / maintenance — starting materials; growth / ruggedness

3) No intrinsic radioactivity or toxic constituents

Overview

Our Directed Search Method

has been used to discover:• Single Crystals SrI2(Eu)

• Transparent Ceramics Garnet(Ce)

• Plastics Bi-loaded Polymer

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Official Use Only


For radioisotope identification, gamma scintillators with

high resolution, low cost and large volume are needed

High resolution enabled by:-High Light Yield

-Low Non-Proportionality

-Uniform Material Response

-Optimized Light Collection

-Accurate Readout

CURRENT FUTURE

Gamma

Scintillation

Detectors

Goals:

• 2% resolution

• Room temperature

• 2000 cm3

• $10/cm3

• No self-activity

NaI(Tl)

• 6% resolution


• 2000 cm3

• $10/cm3

LaX3(Ce)

• 3% resolution


• 400 cm3

• $100/cm3

• Self-activity

P. Dorenbos

SrI2:EuGYGAG:Ce

Bi-loaded plastic

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Official Use Only


Single crystals Ceramics Plastics

Often hygroscopic/air-sensitive

Fragile/brittle

Complex to grow large crystals

Can have gradients & non-

uniformity

Unreactive with air, water

Mechanically durable

Large sizes (100 cm3 Nd:YAG

ceramics commercially available)

Increased activator uniformity

Can form high melting point

oxides

Unreactive with air, water

Mechanically durable

Large sizes, low cost

All crystal structures possible

Best energy resolution

materials- LaBr3(Ce), SrI2(Eu)

~2.6% @ 662 keV

Requires cubic material

Good energy resolution-

GYGAG(Ce) Gadolinium Garnet

~4.5% @ 662 keV w/PMT

Non-standard polymer required

Bi-loading uniformity important

Energy resolution so far ~7% @

662 keV

Inorganic single crystal and ceramic scintillators are being

developed for gamma ray spectroscopy

2 inch

SrI2(Eu)

Bi-loaded polymers,

1 cm3

GYGAG(Ce), 1 in3

http://images.google.com/imgres?imgurl=http://lsd.ornl.gov/BioNanoSysGrp/BNSG/ORNL-Logo.jpg&imgrefurl=http://lsd.ornl.gov/BioNanoSysGrp/BNSG/Scott.htm&h=452&w=772&sz=60&hl=en&start=1&um=1&tbnid=3aMbgjoULPjRzM:&tbnh=83&tbnw=142&prev=/images?q=ornl&um=1&hl=en&sa=N

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For gamma ray spectroscopy, SrI2(Eu) comparable to LaBr3(Ce) and

GYGAG(Ce) is better than NaI(Tl)

300

200

100

0

cou

nts

800600400200

Energy (keV)

NaI(Tl) GYGAG(Ce) LaBr3(Ce)

SrI2(Eu)

Cs-137

101

102

103

104

co

un

ts

400300200100

Energy (keV)


SrI2(Eu)

Ba-1336000

5000

4000

3000

2000

1000

0

Co

un

ts

6040200

Energy (keV)

9.8% Am-241

7.7%

NaI(Tl) LaBr3(Ce)

SrI2(Eu)

x-rays

12.4%

Co

un

tsC

ou

nts

2500

2000

1500

1000

500

0C

ou

nts

14001300120011001000900

Energy (keV)


SrI2(Eu)

6.4%

6.1%

2.0% 1.9%

Co-60

3.3%3.5%

SrI2(Eu) crystals grown at RMD, Inc.

Cut, polished and encapsulated by LLNL

20

16

12

8

4

0En

erg

y R

eso

lutio

n (

%)

3 4 5 6 7 8 9

1002 3 4 5 6 7 8 9

1000Energy (keV)


SrI2(Eu)

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Official Use Only


Comparison of gamma spectra at 662 keV for ~(1”)3 scintillators

reveals effects of resolution and photopeak efficiency, SPP

LaBr3(Ce),

f1.8x2 cm

R=3%

GYGAG(Ce),

f1.1”x0.24”

R=4.7%

• For comparison, 1”x1” Ge photopeak efficiency, SPP = 3.9%

• SPP defined as fraction of gammas intercepting detector that lead to photopeak

SrI2(Eu),

f1”x1”

R=3%

Scintillator SPP (662kev)

for 1”x1” (%)

LaBr3(Ce) 11.1

SrI2(Eu) 11.4

CLYC(Ce) 5.3

NaI(Tl) 8.5

GYGAG(Ce) 12.8

CLYC(Ce),

f1”x1”

R=4.3%

NaI(Tl),

f1”x1”

R=5.8%

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Official Use Only


300

250

200

150

100

50

0

co

un

ts

700600500400300200100

Energy (keV)

2.9% at 662 keV

1 in3

encapsulated crystal

Production of encapsulated SrI2(Eu) underway

Property LaBr3(Ce) SrI2(Eu) Comparison

Melting Point 783 ºC 538 ºC Less thermal stress

Handling Easily cleaves Resists cracking Better processing

Light Yield 60,000 Ph/MeV 90,000 Ph/MeV Higher

Proportionality contribution ~2.0% ~2.0% Favorable

Inhomogeniety 0% >1% (current) Impurities and surfaces being addressed

Decay time 30 nsec 0.5-1.5 msec Fast enough to avoid deleterious signal pile-up

Self-radioactivity La ~ 3x NORM None Less noise

Hygroscopic / air sensitive? Very Very Similar

absorption (2x3”, 662 keV) 22% 24% Similar

1.15

1.10

1.05

1.00

0.95

0.90

Re

lative L

igh

t Y

ield

3 4 5 6 7

102 3 4 5 6 7

1002 3 4 5 6 7

1000Electron Energy (keV)

RMD SrI2(0.5%Eu)

ORNL SrI2(4%Eu)

ORNL SrI2(6%Eu)

Encapsulated RMD SrI2(3%Eu)

NaI(Tl) LaBr3(Ce)

SrI2(Eu): excellent LY

proportionality

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Official Use Only


We have been working to identify an optimal Gd-based

garnet scintillator for the past five years

2006-7 2007-8 2008-9

Composition GAG GYAG GGG GSAG GYSAG GGAG GYGAG

Phase Stability Poor Moderate Excellent Excellent Excellent Moderate Excellent

-LY(Ph/MeV) ___ 40,000 ___ 25,000 30,000 55,000 50,000

En. Res. (662 keV) ___ 11% ___ 11% 10% 9% 4-5%

Current status:

1 in3 parts formed routinely

To optimize performance:

Photodetector matched to green scintillation

2010-11

Scale-up of GYGAG(Ce)

1 in3

5000

4000

3000

2000

1000

0

Co

un

ts

4003002001000

Channel

GYGAG(Ce) ceramic:

4.5% at 662 keV w/ PMT

0 200 400 600

0

500

1000

1500

0.5% 3.9%

Xc = 417

Count

s

MCA Channel

GYGAG_APD_1710V_-23C_6us

GYGAG(Ce) ceramic:

3.9% at 662 keV w/ RMD APD

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Official Use Only


Recently we have developed polymer scintillators

offering energy resolution approaching that of NaI(Tl)

• Non-standard polymer that is

formable by methods similar to

standard plastic scintillator

• Bi organometallic, 40 wt%

• Current size F1.9x0.17 cm3

• Escape peak in small scintillator

eliminated when larger

3

2

1

0

rel. c

ou

nts

6004002000

Energy (keV)

Photopeak662 keV

FWHM = 6.8%simulated 3" x 3"

3

2

1

0

rel. c

ou

nts

Photopeak662 keV

FWHM = 9%

Backscatter escape

BackscatterCompton

edgeEscape 687 keV

A

B

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Official Use Only


Materials for future gamma spectrometers?

Gamma Spectroscopy Scintillator Zeff Light Yld

(Ph/MeV)

En Res,

662 keV

Nonprop

En Res,

662 keV

SPP,

662 keV,

(1 in3)

Single

crystals

NaI(Tl) 50 40,000 7% 5.0% 8.5%

LaBr3(Ce) 44 63,000 3% 2.2% 11.1%

SrI2(Eu) 49 90,000 3% 2.2% 11.4%

Garnet

ceramics

(Gd,Y)3(Al,Ga)5O12(Ce) 47 50,000 4.5% 1.9% 12.8%

Plastics

Standard PVT 4.5 15,000 8% (Compton)

3.5% 0

LLNL Bi-loaded polymers 26 10,000-

30,000

7% 3.5% 1.5%

scintillator materials for gamma ray spectroscopy cherepy forexternal

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