TY - JOUR
T1 - Energy resolution experiments of conical organic scintillators and a comparison with Geant4 simulations
AU - Sosa, C. S.
AU - Thompson, S. J.
AU - Chichester, D. L.
AU - Clarke, S. D.
AU - Di Fulvio, A.
AU - Pozzi, S. A.
N1 - Funding Information:
The authors would like to extend their deepest thanks and gratitude to Dr. Patricia Schuster for her technical expertise, many interesting discussions of organic scintillators, and helpful suggestions during the revision phase. The authors also genuinely thank Mr. Tony Shin for his useful input on statistical uncertainty estimation. This work was funded in-part by the Consortium for Verification Technology under Department of Energy (DOE) National Nuclear Security Administration award number DE-NA0002534 , and Idaho National Laboratory , through its Laboratory Directed Research and Development Program, under DOE Idaho Operations Office contract DE-AC07-05ID14517 .
Publisher Copyright:
© 2018 Elsevier B.V.
PY - 2018/8/1
Y1 - 2018/8/1
N2 - An increase in light-collection efficiency (LCE) improves the energy resolution of scintillator-based detection systems. An improvement in energy resolution can benefit detector performance, for example by lowering the measurement threshold and achieving greater accuracy in light-output calibration. This work shows that LCE can be increased by modifying the scintillator shape to reduce optical-photon reflections, thereby decreasing transmission and absorption likelihood at the reflector boundary. The energy resolution of four organic scintillators (EJ200) were compared: two cones and two right-circular cylinders, all with equal base diameter and height (50 mm). The sides of each shape had two surface conditions: one was polished and the other was ground. Each scintillator was coupled to the center of four photomultiplier tube (PMT) configurations of different diameters. The photocathode response of all PMTs was assessed as a function of position using a small cube (5 mm height) of EJ200. The worst configuration, a highly polished conical scintillator mated to a PMT of equal base diameter, produced a smeared energy spectrum. The cause of spectrum smearing is explored in detail. Results demonstrate that a ground cone had the greatest improvement in energy resolution over a ground cylinder by approximately 16.2% at 478 keVee, when using the largest diameter (127 mm) PMT. This result is attributed to the greater LCE of the cone, its ground surface, and the uniform photocathode response near center of the largest PMT. Optical-photon transport simulations in Geant4 of the cone and cylinder assuming a diffuse reflector and a uniform photocathode were compared to the best experimental configuration and agreed well. If a detector application requires excellent energy resolution above all other considerations, a ground cone on a large PMT is recommended over a cylinder.
AB - An increase in light-collection efficiency (LCE) improves the energy resolution of scintillator-based detection systems. An improvement in energy resolution can benefit detector performance, for example by lowering the measurement threshold and achieving greater accuracy in light-output calibration. This work shows that LCE can be increased by modifying the scintillator shape to reduce optical-photon reflections, thereby decreasing transmission and absorption likelihood at the reflector boundary. The energy resolution of four organic scintillators (EJ200) were compared: two cones and two right-circular cylinders, all with equal base diameter and height (50 mm). The sides of each shape had two surface conditions: one was polished and the other was ground. Each scintillator was coupled to the center of four photomultiplier tube (PMT) configurations of different diameters. The photocathode response of all PMTs was assessed as a function of position using a small cube (5 mm height) of EJ200. The worst configuration, a highly polished conical scintillator mated to a PMT of equal base diameter, produced a smeared energy spectrum. The cause of spectrum smearing is explored in detail. Results demonstrate that a ground cone had the greatest improvement in energy resolution over a ground cylinder by approximately 16.2% at 478 keVee, when using the largest diameter (127 mm) PMT. This result is attributed to the greater LCE of the cone, its ground surface, and the uniform photocathode response near center of the largest PMT. Optical-photon transport simulations in Geant4 of the cone and cylinder assuming a diffuse reflector and a uniform photocathode were compared to the best experimental configuration and agreed well. If a detector application requires excellent energy resolution above all other considerations, a ground cone on a large PMT is recommended over a cylinder.
KW - Compton-coincidence technique
KW - Energy resolution
KW - Light-collection efficiency
KW - Organic scintillator
KW - Photocathode non-uniformity
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U2 - 10.1016/j.nima.2018.04.058
DO - 10.1016/j.nima.2018.04.058
M3 - Article
AN - SCOPUS:85047114999
SN - 0168-9002
VL - 898
SP - 77
EP - 84
JO - Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
JF - Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
ER -