Nonproportionality Studies in Single Crystal Scintillators: Towards Improved Energy Resolution for Nuclear and Radiological Detectors. Bi-annual Spanish Conference in Physics. Santander, Sept. 24th, 2011

1. M. Gascón, S. Lam, R. Gaumé, R. Feigelson AOCL Stanford University Sept. 26th, 2011 1
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Nonproportionality Studies in Single Crystal
Scintillators:
Towards Improved Energy Resolution for Nuclear
and Radiological Detectors
M. Gascón, S. Lam, R. Gaume, R. Feigelson
Dept. of Material Science & Engineering, Stanford University
Sept. 26Th
, 2011

2. M. Gascón, S. Lam, R. Gaumé, R. Feigelson AOCL Stanford University Sept. 26th, 2011 2
Overview
Comments
Motivation & background
Modeling
Temperature and Pressure studies
Conclusions

3. M. Gascón, S. Lam, R. Gaumé, R. Feigelson AOCL Stanford University Sept. 26th, 2011 3
Motivation: Scintillator applications
Comments
Petroleum Engineering
Medical Imaging
Scintillators
High­Energy Physics
Nuclear Radiation
Detection

4. M. Gascón, S. Lam, R. Gaumé, R. Feigelson AOCL Stanford University Sept. 26th, 2011 4
Motivation: scintillators history
M. J. Weber, J. Lumin. 100 (2002) 35
SrI2:Eu 1968/2008
LSO:Ce,Ca 2007
LuI3:Ce 2003
LaBr3:Ce 2001
LYSO:Ce 2001
LuYAP:Ce 2001
LaCl3:Ce 2000
LuAP:Ce 1994
LSO:Ce 1982
Invention
of the PMT
CWE van Eijk, SCINT 2011
Robert Hofstadter

5. M. Gascón, S. Lam, R. Gaumé, R. Feigelson AOCL Stanford University Sept. 26th, 2011 5
Motivation: Energy resolution
CWE van Eijk, SCINT 2011

6. M. Gascón, S. Lam, R. Gaumé, R. Feigelson AOCL Stanford University Sept. 26th, 2011 6
Motivation: Nonproportionality in light yield
Light yield
(relative to 662 keV)

7. M. Gascón, S. Lam, R. Gaumé, R. Feigelson AOCL Stanford University Sept. 26th, 2011 7
Motivation: Nonproportionality in light yield
Light yield
(relative to 662 keV)

8. M. Gascón, S. Lam, R. Gaumé, R. Feigelson AOCL Stanford University Sept. 26th, 2011 8
Motivation: Temperature studies

9. M. Gascón, S. Lam, R. Gaumé, R. Feigelson AOCL Stanford University Sept. 26th, 2011 9
Modeling: Pressure
DSSSD
Large Nonproportionality
LuAlO
3
conduction band
valence band
Small Nonproportionality
K2LaCl5
valence band
conduction band
dip: ↑ NPno dip: ↓ NP
Difference in charge carrier mobilities.

10. M. Gascón, S. Lam, R. Gaumé, R. Feigelson AOCL Stanford University Sept. 26th, 2011 10
Light Yield Nonproportionality: Modeling
DSSSD
Observation of band structure
of YAlO3 (YAP) and LuAlO3
(LuAP). YAP and LuAP have the
same crystal structure, but
exhibit very different
nonproportionality.
good proportionality poor proportionality
Similar band dispersion except for the presence of “dip” in conduction band
minimum (CBM) of LuAP as indicated with the arrow
valence
band
X Y
Z
U R
T
S
1st
Brillouin
Zone

11. M. Gascón, S. Lam, R. Gaumé, R. Feigelson AOCL Stanford University Sept. 26th, 2011 11
Motivation: Pressure experiment
Mobilities of charge carriers better matched

12. M. Gascón, S. Lam, R. Gaumé, R. Feigelson AOCL Stanford University Sept. 26th, 2011 12
Isostatic pressure
http://harwoodeng.com/
Specifications:
Pressure range: 0<Piso<1 GPa
Large sample volume: >5 cm3
Operated at ambient temperature
Compatible with hygroscopic materials
Good pressure stability

13. M. Gascón, S. Lam, R. Gaumé, R. Feigelson AOCL Stanford University Sept. 26th, 2011 13
Facilities
High pressure studies: Eu:SrI2, BGO, Tl: CsI, LSO

14. M. Gascón, S. Lam, R. Gaumé, R. Feigelson AOCL Stanford University Sept. 26th, 2011 14
Isostatic pressure
Recall assumptions:
Pressure stability
Pressure dependence
of optical coupling scintillator with
window & reflector
Light output correction neededGood pressure stability
|DP/P| < 1% after 1 hr

15. M. Gascón, S. Lam, R. Gaumé, R. Feigelson AOCL Stanford University Sept. 26th, 2011 15
Isostatic pressure
There is an increase in Light Output up to
50%
The optical coupling contribution was
subtracted

16. M. Gascón, S. Lam, R. Gaumé, R. Feigelson AOCL Stanford University Sept. 26th, 2011 16
Conclusions
Adequate detection and identification of radioactive material require
scintillators with good light yield proportionality and energy resolution
Light yield proportionality requires an effective mass ratio of 1 (well
matched charge carrier mobilities)
Nonproportionality and carrier mobility can be probed through
application of high pressure and low temperature
This program is funded by the USA Domestic Nuclear
Detection Office (DNDO) and Dept. of Homeland
Security (DHS).

17. M. Gascón, S. Lam, R. Gaumé, R. Feigelson AOCL Stanford University Sept. 26th, 2011 17
Recall assumptions:

18. M. Gascón, S. Lam, R. Gaumé, R. Feigelson AOCL Stanford University Sept. 26th, 2011 18
Decay time
Pulse were inverted
N Pulses were added after rise time correction
Pulses with amplitudes bigger 0.4 (normalized)
before ­0.5 us and after 2.5 us were discarded to avoid
pile up.
Pulses with amplitudes below 1 mV were discarded.
Comments

19. M. Gascón, S. Lam, R. Gaumé, R. Feigelson AOCL Stanford University Sept. 26th, 2011 19
Non Proportionality
Radioactive sources and energies
Cs­137..... 32 keV and 662 keV
Ba­133..... 31 keV, 81 keV, 302 keV, 356 keV
Am­241.... 26 keV and 59.5 keV
Cd­109..... 22 keV and 88 keV
Co­57 …...122 keV
Na­22........511 keV and 1274 keV
Mn­54.......835 keV
Eu­152......41 keV, 121 keV and 1408 keV
Cs-137
Ba-133
Am-241 Cd-109
Comments
Fitting an extra peak can displace
the peaks 5­10 channels which
means a huge change in NP at low
energies

20. M. Gascón, S. Lam, R. Gaumé, R. Feigelson AOCL Stanford University Sept. 26th, 2011 20
Non Proportionality
Radioactive sources and energies
Cs­137..... 32 keV and 662 keV
Ba­133..... 31 keV, 81 keV, 302 keV, 356 keV
Am­241.... 26 keV and 59.5 keV
Cd­109..... 22 keV and 88 keV
Co­57 …...122 keV
Na­22........511 keV and 1274 keV
Mn­54.......835 keV
Eu­152......41 keV, 121 keV and 1408 keV
Co-57
Na-22
Mn-54 Eu-152
Comments
Co­57 has an additional peak below 122
keV which is not in the tables
Na and Mn are easily fit­able
Eu has 41, 121 and 1408 are easily fit­able