1205 sr i2 cherepy f

Lawrence Livermore National Laboratory

This work performed under the auspices of the U.S. Department of Energy by

Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344

Instrument Development and Gamma Spectroscopy

with Strontium Iodide May 16, 2012

Funded by

DHS/DNDO

LLNL-PRES-557601

This work has been supported by the US Department of

Homeland Security, Domestic Nuclear Detection Office,

under competitively awarded IAA HSHQDC-09-x-00208 /

P00002. This support does not constitute an express or

implied endorsement on the part of the Government.

N.J. Cherepy ([email protected])

S.A. Payne, B.W. Sturm, O.B. Drury, S.P. O’Neal and P. Thelin

Lawrence Livermore National Laboratory, Livermore, CA 94550

K. Shah, R. Hawrami, U. Shirwadkar and team Radiation Monitoring Devices

M. Momayezi, B. Hurst and team Bridgeport Instruments

A. Burger, E. Rowe, E. Tupitsyn, P. Bhattacharya, Y. Cui, M. Groza, V. Buliga and team Fisk University

L.A. Boatner, J.O. Ramey and team Oak Ridge National Laboratory

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

http://www.bridgeportinstruments.com/index.html

mailto:[email protected]

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Official Use Only Official Use Only CFP06-TA01-LL01 Cherepy

Title: High Resolution Scintillator Materials and Detectors N. CHEREPY [email protected]

Where did SrI2(Eu) come from?

• SrI2(Eu) – perfect match between Sr & Eu ionic radii = high doping, with high uniformity

X

X

AX2

Strontium Iodide: Uniform Eu-doping, No cleavage plane, No intrinsic radioactivity

Equivalent to LaBr3(Ce) - Stopping and Energy resolution

• CaI2(Eu) reported by Hofstadter in 1960’s 100,000 Ph/MeV, but laminar growth habit

• In 2006, our team started growing the nice, orthorhombic crystal BaI2(Eu) 60,000 Ph/MeV,

BUT Eu not a good match to Ba ionic radius, poor doping uniformity and poor energy resolution

Ionic Radii:

Sr = 1.40 Å

Eu = 1.41 Å

Ba = 1.56 Å

Ca = 1.26 Å

• Later, we found out that Hofstadter had tried SrI2(Eu) in 1960’s, but had used Eu3+ dopant at very low

concentrations LY lower than NaI(Tl), so he abandoned it and no papers in literature on SrI2(Eu)

Alkaline Earth Iodides

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Since its discovery in Oct 2007, have learned how to grow, polish,

encapsulate and instrument Strontium Iodide for high performance

SrI2(Eu) Growth

1200

1000

800

600

400

200

0

Co

un

ts

800600400200

Energy (keV)

2.7%

SrI2(Eu) single crystal performance for gamma spectroscopy is comparable to that of LaBr3(Ce)

1 in3 crystal – Analog Readout

SrI2(Eu) polishing and shaping

1.6 in3

crystal

Encapsulated crystal

under UV excitation

Demonstrated reproducible quality of

crystals and encapsulation procedure

• N.J. Cherepy, G. Hull, A. Drobshoff, S.A. Payne, E. van Loef, C.

Wilson, K. Shah, U.N. Roy, A. Burger, L.A. Boatner, W-S Choong,

W.W. Moses “Strontium and Barium Iodide High Light Yield

Scintillators,” Appl. Phys. Lett. 92, 083508 (2008).

• B.W. Sturm, N.J. Cherepy, O.B. Drury, P.A. Thelin, S.E. Fisher,

S.A. Payne, A. Burger, L.A. Boatner, J.O. Ramey, K.S. Shah, R.

Hawrami, “Effects of Packaging SrI2(Eu) Scintillator Crystals,”

Nucl. Instr. Meth. A, 652, 242-246 (2011).

SrI2(Eu) Gamma Spectrum

Cs-137 source

1.5” diameter

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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4

3

2

1

I (a

.u.)

700600500400300

wavelength (nm)

2500

2000

1500

1000

500

0

STE

Eu2+

Impurity-mediated recombination

Eg = 5eV

Exciton

Absorption, 100 um SrI2(3%Eu)

updoped SrI2

4

3

2

1

I (a

.u.)

700600500400300

wavelength (nm)

2500

2000

1500

1000

500

0

Eu2+

Absorption, 100 um SrI2(3%Eu)

1000

800

600

400

200

0

co

un

ts

1.2MeV1.00.80.60.40.20.0

Energy

undoped SrI2 SrI2(3%Eu)

FWHM=5.28%

FWHM=2.85%

Strontium Iodide scintillator characteristics

Undoped:

t = 0.42 ms

3% Eu-doped 1 in3

encapsulated crystal:

t = 3.3 ms average decay time

Digitized

scintillation pulses,

662 keV

Radioluminescence

Eu-doped Undoped

Undoped

SrI2(3%Eu)

Cs-137 Pulse Height Spectra

R =

5.3% R =

2.8%

1.0

0.9

0.8

0.7

0.6

0.5

Re

l. L

Y

12 3 4 5 6

102 3 4 5 6

1002 3 4 5 6

1000Electron Energy (keV)

Undoped SrI2 SrI2(3%Eu)

Light Yield Proportionality

Energy(MeV)

RNP =

3.8%

2.2%

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Properties of some gamma spectroscopy scintillators

NaI(Tl) LaBr3(Ce) SrI2(Eu) GYGAG(Ce) Bi-loaded

plastic

Light Yield (Ph/MeV) 38,000 65,000 100,000 55,000 40,000

Emission peak (nm) 415 380 435 540 500

Principal decay (ns) 230 17 1200 250 1250

Density (g/cm3) 3.67 5.10 4.59 5.8 1.4

Zeff 50 44 49 47 26

Melting / Process

Temp (°C) 651 783 538

1800

(sinter, <24 h) 75

Crystal Structure cubic hexagonal orthorhombic cubic amorphous

En. Res. w/ PMT

(% @ 662 keV) 7% 2.7% 2.7% 4.5% 8%

• N.J. Cherepy, S.A. Payne, B.W. Sturm, S.P O’Neal, Z.M. Seeley, O.B. Drury, L.K. Haselhorst, B.L. Rupert, R.D. Sanner, P.A. Thelin, S.E. Fisher, R. Hawrami,

K.S. Shah, A. Burger, J. O. Ramey, L.A. Boatner, “Performance of Europium-Doped Strontium Iodide, Transparent Ceramics and Bismuth-loaded Polymer

Scintillators,” Proc. SPIE, 8142, 81420W (2011).

• N.J. Cherepy, S.A. Payne, B.W. Sturm, J.D. Kuntz, Z.M. Seeley, B.L. Rupert, R.D. Sanner, O.B. Drury, T.A. Hurst, S.E. Fisher, M. Groza, L. Matei, A. Burger,

R. Hawrami, K.S. Shah, L.A. Boatner, “Comparative gamma spectroscopy with SrI2(Eu), GYGAG(Ce) and Bi-loaded plastic scintillators,” IEEE Nuc. Sci. Symp.

Conf. Record, p. 1288 - 1291 (2010).

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… Difficult to avoid some level of

light-trapping in SrI2(Eu)

“Light-trapping” occurs in Eu-doped scintillators due to small Stokes’ Shift

and is a function of Eu-doping level, standard doping is 3%

Successive emissions, followed by re-absorption then re-emission (etc.), causes

effective lengthening of decay- no problem unless accompanied by a loss mechanism

Eu2+

CB

VB

freabsorbed = 80%

J. Glodo, E. V. van Loef, N. J. Cherepy, S. A. Payne, and

K. S. Shah, "Concentration Effects in Eu Doped SrI2," IEEE

Trans. Nucl. Sci., vol. 57, pp. 1228-1232, (2010).

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Digital readout may be employed to improve energy resolution of

large and/or highly Eu-doped crystals

• Inverse correlation between decay time and pulse height

• Events may be corrected based on pulse shape, and energy histogram

made more accurate

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Encapsulated 1.6 in3 crystal shows high energy tailing with analog readout,

digital acquisition and FPGA pulse processing 3% at 662 keV

1000

800

600

400

200

0

co

un

ts

2000150010005000

channel

1_SrI2_pack78-1_1111213.8195%

HV=-900Vtau=12usG=2.5

1000

800

600

400

200

0

co

un

ts

800x1036004002000

Energy (keV)

Crystal 78-1, 1.6 in3

R = 2.97%

Vol = 1.6 in3

ANALOG

R = 3.8%

with tail

DIGITAL

R = 3.0%

No tail Best SrI2(Eu) resolution ever:

Measured with 1 cm3 Fisk crystal

ANALOG

R = 2.51%

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100

101

102

103

104

1000800600400200

Energy (keV)

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

SrI2(Eu)

Germanium

Thorium-232

Scintillator detectors are useful for isotope identification

via gamma ray spectroscopy

Safeguards and

Homeland Security

Ge spectrum courtesy of Morgan Burks, LLNL

Spectra shifted for clarity

False Alarm Rate:

FAR* ~ R3.4 / (Spp / BTOT)0.54

* Formula derived from: K.E. Nelson, T. Gosnell, D. Knapp, “The effect of gamma ray detector energy resolution on the ability

to identify unknown radioactive sources,” LLNL-TR-411374 (Feb. 2009).

False alarm rate is strongly dependent on energy

resolution – small improvement makes a big difference

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101

102

103

104

105

140012001000800600400200

Energy (keV)

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

SrI2(Eu)

Germanium

Radium-226


Ge spectrum courtesy of M. Burks, LLNL

Comparison of gamma spectroscopy performance

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SrI2(Eu) has no intrinsic radioactivity

100

101

102

103

104

200015001000500

Energy (keV)

NaI(Tl) GYGAG(Ce) SrI2(Eu)

LaBr3(Ce)

U

K-40

ThU

ThU

ThTh U

U

Th

Background

138La, 1470

138La, 789, b’s

a’s


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• Digital acquisition with “on-the-fly” FPGA pulse processing

• R<3% at 662 keV

• Robust approach for providing high resolution gamma spectroscopy

with large-size crystals

Compact SrI2(Eu) handheld radioisotope identification detector (RIID)

prototype using small COTS components, embedded computing

7”

3”

• 1.2” x 1.5” crystal

• PMT

• HV base

• Pulse digitizer

• MCA

• 7” x 3”

computer

• 550 g

• 20 hr battery

Instrument Features:

• Energy Calibration

• Dose rate

• Spectrum

http://www.bridgeportinstruments.com/index.html

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1.0

0.8

0.6

0.4

0.2

0.0

Re

l. L

Y

3002001000-100

Temperature (°C)

Decrease from RT to

150 °C of 8%

SrI2(5%Eu)

• T-dependence of LY is comparable for SrI2(Eu) and LaBr3(Ce)

• Minimal temperature stabilization required in instrument

Eu-doped Strontium Iodide offers a light yield that is stable around room

temperature, and has potential to be useful at high temperatures

M.S. Alekhin, J.T.M. de Haas, K.W. Krämer, I.V. Khodyuk,

L. de Vries, P. Dorenbos, “Scintillation properties and self

absorption in SrI2:Eu2+” IEEE TNS , 58, 2519-2527 (2010).

LaBr3(5%Ce) Decrease from RT

to 150 °C of ~5%

M.D. Birowosuto,P. Dorenbos, K.W. Krämer, H.U. Gudel

“Ce3+ activated LaBr3-xIx: High-light-yield and fast-

response mixed halide scintillators” J. Appl. Phys,

103 , 103517 (2008).

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SrI2(Eu) is on track to becoming a practical scintillator for RIID applications

• SrI2(Eu) - high light yield, good proportionality, blue emission and R(662 keV) =2.5-3%

• Low melting point, perfect lattice match between Sr and Eu

• Single crystals of 2” diameter demonstrated

• Encapsulation improves optical coupling; hermetic seal is stable

• Light trapping mitigated by high quality surface polish, geometry and digital processing

• High resolution and no intrinsic radioactivity improves detectability of weak sources

1000

800

600

400

200

0

co

un

ts

2000150010005000

channel

HV=-880Vtau=12usG=2.5

1_SrI2_121-1_1202072.9891%

Growth and

encapsulation

established High resolution, Large size

Compact detector demonstrated

R = 3%

with 3.2 in3 SrI2(Eu)

1205 sr i2 cherepy f

Documents

cherepy official use

high doping

eu sri23

official use onlyproperties

high uniformity

uniform eudoping

sr eu ionic radii

instrument strontium