Non-proportionality studies through the application of high isostatic pressure
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Transcript of 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
M. Gascón, S. Lam , R. Feigelson LUMDETR 2012, Halle, Germany September 11th, 2012 2
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
M. Gascón, S. Lam , R. Feigelson LUMDETR 2012, Halle, Germany September 11th, 2012 3
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
M. Gascón, S. Lam , R. Feigelson LUMDETR 2012, Halle, Germany September 11th, 2012 4
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.
M. Gascón, S. Lam , R. Feigelson LUMDETR 2012, Halle, Germany September 11th, 2012 5
Modeling: NP vs. effective mass ratio
charge carriers mobility better matched
W. Setyawan, R. Gaume, R. Feigelson, S. Curtarolo, IEEE Transactions on Nuclear Science, Vol 56, No. 5, October 2009.
Mo
re p
rop
ort
i on
al
M. Gascón, S. Lam , R. Feigelson LUMDETR 2012, Halle, Germany September 11th, 2012 6
How can we study NP experimentally?
Isostatic pressure
M. Gascón, S. Lam , R. Feigelson LUMDETR 2012, Halle, Germany September 11th, 2012 7
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.
M. Gascón, S. Lam , R. Feigelson LUMDETR 2012, Halle, Germany September 11th, 2012 8
Pressure studies – Experimental results
Light Output Energy Resolution
M. Gascón, S. Lam , R. Feigelson LUMDETR 2012, Halle, Germany September 11th, 2012 9
Pressure studies: CsI(Tl)
CsI(Tl)
↑ P, ↓ Decay time We need to improve the precision in LO
Isostatic Pressure (MPa)
Decay Time Nonproportionality
M. Gascón, S. Lam , R. Feigelson LUMDETR 2012, Halle, Germany September 11th, 2012 10
Pressure studies: CsI(Tl)
CsI(Tl)
↑ P, ↓ Decay time Best proportionality at ~160 MPa
Isostatic Pressure (MPa)Isostatic Pressure (MPa)
Decay Time Nonproportionality
M. Gascón, S. Lam , R. Feigelson LUMDETR 2012, Halle, Germany September 11th, 2012 11
Pressure studies: LaBr3(Ce)
Decay Time Nonproportionality
↑ P, ↓ Decay time↑ P, ↓ NP60/662, less proportional
Nonproportionality
M. Gascón, S. Lam , R. Feigelson LUMDETR 2012, Halle, Germany September 11th, 2012 12
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
M. Gascón, S. Lam , R. Feigelson LUMDETR 2012, Halle, Germany September 11th, 2012 13
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
M. Gascón, S. Lam , R. Feigelson LUMDETR 2012, Halle, Germany September 11th, 2012 14
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
M. Gascón, S. Lam , R. Feigelson LUMDETR 2012, Halle, Germany September 11th, 2012 15
Modeling: NP vs. effective mass ratio
charge carriers mobility better matched
W. Setyawan, R. Gaume, R. Feigelson, S. Curtarolo, IEEE Transactions on Nuclear Science, Vol 56, No. 5, October 2009.
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
M. Gascón, S. Lam , R. Feigelson LUMDETR 2012, Halle, Germany September 11th, 2012 16
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
M. Gascón, S. Lam , R. Feigelson LUMDETR 2012, Halle, Germany September 11th, 2012 17
Pressure studies: Light Output and Band Gap energies
Band Gap Calculations
LO = k. E β.Egap
M. Gascón, S. Lam , R. Feigelson LUMDETR 2012, Halle, Germany September 11th, 2012 18
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)