TY - JOUR
T1 - Plastic scintillator response to low-energy photons
AU - Williamson, J. F.
AU - Dempsey, J. F.
AU - Kirov, A. S.
AU - Monroe, J. I.
AU - Binns, W. R.
AU - Hedtjärn, H.
PY - 1999/4
Y1 - 1999/4
N2 - The plastic scintillator (PS) is a promising dosimeter for brachytherapy and other low-energy photon applications because of its high sensitivity and approximate tissue equivalence. As part of our project to develop a new PS material which maximizes sensitivity and radiological equivalence to water, we have measured the response, ε (light output/unit air kerma), of PS to low-energy bremsstrahlung (20 to 57 keV average energies) x-rays as well as photons emitted by 99mTc, 192Ir, and 137Cs sources, all of which were calibrated in terms of air kerma. The PS systems studied were a standard commercial PS, BC400 (Bicron Corporation, Newbury, OH), and our new sensitive and quench-resistant scintillator (polyvinyltoluene base and binary dye system) with and without 4% Cl loading intended to match the effective atomic number of water. For low-energy x-rays; ε was 20-57% relative to ε for 192Ir photons. Chlorine loading clearly reduced the energy dependence of ε, which ranged from 46% to 85% relative to 192Ir. However, even after using Monte Carlo photon-transport simulation to correct for the non-air equivalence of the PS, inherent dosimetric sensitivity still varied by 30% over the 20-400 keV energy range. Our work, one of the few measurements of PS response to low-energy photons, appears to confirm Birks' 1955 finding that ionization quenching reduces sensitivity to electrons below 125 keV. However, our results cannot be explained by Birks' widely used unimolecular quenching model.
AB - The plastic scintillator (PS) is a promising dosimeter for brachytherapy and other low-energy photon applications because of its high sensitivity and approximate tissue equivalence. As part of our project to develop a new PS material which maximizes sensitivity and radiological equivalence to water, we have measured the response, ε (light output/unit air kerma), of PS to low-energy bremsstrahlung (20 to 57 keV average energies) x-rays as well as photons emitted by 99mTc, 192Ir, and 137Cs sources, all of which were calibrated in terms of air kerma. The PS systems studied were a standard commercial PS, BC400 (Bicron Corporation, Newbury, OH), and our new sensitive and quench-resistant scintillator (polyvinyltoluene base and binary dye system) with and without 4% Cl loading intended to match the effective atomic number of water. For low-energy x-rays; ε was 20-57% relative to ε for 192Ir photons. Chlorine loading clearly reduced the energy dependence of ε, which ranged from 46% to 85% relative to 192Ir. However, even after using Monte Carlo photon-transport simulation to correct for the non-air equivalence of the PS, inherent dosimetric sensitivity still varied by 30% over the 20-400 keV energy range. Our work, one of the few measurements of PS response to low-energy photons, appears to confirm Birks' 1955 finding that ionization quenching reduces sensitivity to electrons below 125 keV. However, our results cannot be explained by Birks' widely used unimolecular quenching model.
UR - http://www.scopus.com/inward/record.url?scp=0032969771&partnerID=8YFLogxK
U2 - 10.1088/0031-9155/44/4/004
DO - 10.1088/0031-9155/44/4/004
M3 - Article
C2 - 10232801
AN - SCOPUS:0032969771
SN - 0031-9155
VL - 44
SP - 857
EP - 871
JO - Physics in medicine and biology
JF - Physics in medicine and biology
IS - 4
ER -