Nonproportionality Studies in Single Crystal Scintillators: Towards Improved Energy Resolution for...
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Transcript of Nonproportionality Studies in Single Crystal Scintillators: Towards Improved Energy Resolution for...
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
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
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
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 1968/2008LSO:Ce,Ca 2007LuI3:Ce 2003LaBr3:Ce 2001LYSO:Ce 2001LuYAP:Ce 2001LaCl3:Ce 2000LuAP:Ce 1994LSO:Ce 1982
Invention of the PMT
CWE van Eijk, SCINT 2011
Robert Hofstadter
M. Gascón, S. Lam, R. Gaumé, R. Feigelson AOCL Stanford University Sept. 26th, 2011 5
Motivation: Energy resolution
CWE van Eijk, SCINT 2011
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)
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)
M. Gascón, S. Lam, R. Gaumé, R. Feigelson AOCL Stanford University Sept. 26th, 2011 8
Motivation: Temperature studies
M. Gascón, S. Lam, R. Gaumé, R. Feigelson AOCL Stanford University Sept. 26th, 2011 9
Modeling: Pressure
DSSSD
Large Nonproportionality
LuAlO3
conduction band
valence band
Small Nonproportionality
K2LaCl5
valence band
conduction band
dip: ↑ NP no dip: ↓ NP
Difference in charge carrier mobilities.
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
vale
nce
band
X Y
ZU R
T
S
1st BrillouinZone
M. Gascón, S. Lam, R. Gaumé, R. Feigelson AOCL Stanford University Sept. 26th, 2011 11
Motivation: Pressure experiment
Mobilities of charge carriers better matched
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
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
M. Gascón, S. Lam, R. Gaumé, R. Feigelson AOCL Stanford University Sept. 26th, 2011 14
Isostatic pressure
Recall assumptions:
Pressure stabilityPressure dependence
of optical coupling scintillator with window & reflector
Light output correction neededGood pressure stability |DP/P| < 1% after 1 hr
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
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).
M. Gascón, S. Lam, R. Gaumé, R. Feigelson AOCL Stanford University Sept. 26th, 2011 17
Recall assumptions:
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
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
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