non-proportionality studies through the application of high isostatic pressure

M. Gascón, S. Lam , R. Feigelson LUMDETR 2012, Halle, Germany September 11th, 2012 1

Non-proportionality studies through the application of high isostatic pressure

Martín Gascón, Stephanie Lam, Robert Feigelson Dept. of Material Science and Engineering, Stanford University

LUMDETR 2012, Halle, Germany September 11th, 2012

Wahyu Setyawan, Shidong Wang, Stefano Curtarolo Mechanical Engineering and Material Science, Duke University


Outline

I. Motivation

II. Computational work

III. Experimental results

Light output and energy resolution

Decay time and Non-proportionality

Challenges

IV. Summary and future work


Energy (keV)

Lig

ht

ou

tpu

t (r

el.

66

2 k

eV)

Scintillator nonproportionality is dependent on:

● Crystal structure● Dopant concentration● Concentration in cation-substituted

materials● Crystal quality

Mengesha et al. IEEE Trans. Nucl. Sci., 45, 3, 1998.

How can we relate nonproportionality to crystal structure and charge interactions

through the application of isostatic pressure?

Motivation


Modeling

DSSSD

Less proportional

YAlO3

conduction band

valence band

More proportional

valence band

conduction band

dip: ↑ NP

no dip: ↓ NP

CsI

W. Setyawan, R. Gaume, R. Feigelson, S. Curtarolo, IEEE Transactions on Nuclear Science, Vol 56, No. 5, October 2009.


Modeling: NP vs. effective mass ratio

charge carriers mobility better matched


Mo

re p

rop

ort

i on

al


How can we study NP experimentally?

Isostatic pressure


Isostatic pressure - Instrumentation

Specifications: Pressure range: 0 - 1 GPa (10 kbar, 145 kpsi)

Large sample volume: < 5 cm3 Operated at ambient temperature Compatible with hygroscopic materials Good pressure stability

Control panel Pressure vessel

30 cm

Heptane

Sapphire window

PMT

Optical grease

Scintillator

316 Steel1.5”

Heptane in

First large-volume isostatic pressure scintillation instrumentation:

R. Gaume, M. Gascon, S. Lam, R. Feigelson, W Setyawan, S. Curtarolo, Review of Scientific Instruments, submitted 2012.


Pressure studies – Experimental results

Light Output Energy Resolution


Pressure studies: CsI(Tl)

CsI(Tl)

↑ P, ↓ Decay time We need to improve the precision in LO

Isostatic Pressure (MPa)

Decay Time Nonproportionality


Pressure studies: CsI(Tl)

CsI(Tl)

↑ P, ↓ Decay time Best proportionality at ~160 MPa

Isostatic Pressure (MPa)Isostatic Pressure (MPa)



Pressure studies: LaBr3(Ce)


↑ P, ↓ Decay time↑ P, ↓ NP60/662, less proportional

Nonproportionality


Sample degradation in heptane

CsI(Tl)

∆LO ~ -0.5 %/ day

Pressure studies: Challenges

Hysteresis effect

➔ Better peak fitting algorithm due to low light output conditions: poor optical coupling (sapphire window) between sample and PMT

➔ Corrections for light output needed between experimental runs due to:

Optical grease

Scintillator

Heptane

Sapphire window

PMT

Heptane in


Summary

● Identified a correlation between NP and band structure: Better proportionality at low effective mass ratio (~1)

● Studied NP, light output, decay time, and energy resolution at high pressure for CsI(Tl) and LaBr3(Ce)

Future Work

● Measure CLYC, LSO(Ce) and NaI(Tl)

● Reach higher pressures (different compressible fluids)

● Improve design of pressure instrumentation


Radioactive sources and energies

Acknowledgments

Duke UniversityStanford University

This work is supported by the U.S. Dept. of Homeland Security/DNDO grant no. 2008-DN-077-ARI005-03-4 and carried out at:

Contributors:Stephanie Lam, Romain Gaume, Eric Xu, Robert Feigelson (Stanford University)Wahyu Setyawan, Shidong Wang, Stefano Curtarolo (Duke University)

Thanks to the LUMDETR 2012 organization committee


Modeling: NP vs. effective mass ratio

charge carriers mobility better matched


non-Vk

Vk

Free carriers in Vk compounds- Vk-centers act as additional traps- Effective trapping in isotropic media → less proportional

Free carriers in non-Vk compounds- Spatial distribution of free e/h depends on mass ratio. - When free e/h are near luminescent centers, loss decreases → more propotional

Mo

re p

rop

ort

i on

al


Isostatic pressure studies - Background

Past pressure studies have typically been uniaxial or utilize anvil cells for isostatic pressure studies on sub-mm sized samples.

Uniaxial - CsI(Tl) Light Output

Hydrostatic - CsIDecay Time & Luminescence Spectra

Gayshan et al. Nucl. Instr. Meth. A 505, (2003), 97-100 Tsujimoto et al. Phys. Rev. B., 54, 23, (1996), 16579-16584


Pressure studies: Light Output and Band Gap energies

Band Gap Calculations

LO = k. E β.Egap


Pressure studies: Light Output and Band Gap energies

LO = k. E

β.Egap

Linewidth Collapse in Three-Photon Exciton-Polariton Spectra of CsI under PressureC. H. Yoo,* M. J. LippPRB v84 pp. 3875-3878 (2000)


Pressure studies: Non-proportionality

LaBr3(Ce)CsI(Tl)