Measured neutron light-output response for trans-stilbene and small-molecule organic glass scintillators

Abstract

Abstract The neutron light-output response from quasi-monoenergetic neutrons was measured for a O5.08 × 5.08 cm trans-stilbene and a O5.08 × 5.08 cm small-molecule organic glass scintillator . Quasi-monoenergetic neutrons were isolated from a time-of-flight measurement of a Cf-252 spontaneous fission source with a flight distance of 200 cm. Two different methods of waveform analysis were implemented, where the neutron light output response proportional to the detected pulse height distribution (PHD) and pulse integral distribution (PID) were extracted for both types of scintillators. The light output response proportional to the pulse integral was determined by integrating the digitized waveform with an integration window length of 150 ns, which contained > 90% and > 95% of the scintillation light for an averaged neutron and photon waveform above 0.5 MeVee. The extracted light-output data were fitted with a semi-empirical function based on the Birks’ formula. The results show that the small-molecule organic glass scintillator produced more light than the trans-stilbene scintillator for a range of neutron energies of 0.79 ± 0.04 MeV to 3.65 ± 0.38 MeV. The fitted semi-empirical function was used in MCNPX-PoliMi with MPPost to simulate the detector response from an independent measurement of a Cf-252 spontaneous fission source to test the fidelity of the extracted light output response functions. The simulated and measured total neutron count rate agreed to within ± 3 % and ± 1% for the trans-stilbene and small-molecule organic glass scintillators. Due to the different light-output response of the two scintillators, the intrinsic neutron detection efficiency was calculated for equal observable ranges in light output and neutron-equivalent energy units. The intrinsic neutron detection efficiency in the observable light-output range of 0.06 MeVee to 2.4 MeVee was calculated to be 28.66 ± 1.43 % and 34.66 ± 1.73 % for pulse height and pulse integral analysis, respectively. For the same observable light-output range, the intrinsic efficiency of small-molecule organic glass was calculated to be 32.54 ± 1.63 % and 37.39 ± 1.87 % for pulse height and pulse integral analysis, respectively. When observing equal light-output ranges, the small-molecule organic glass was 11.92 ± 6.23% and 7.88 ± 7.35% more efficient than the trans-stilbene using pulse height and pulse integral analysis, respectively. When observing equal neutron-equivalent energy ranges, the trans”–stilbene scintillator was 8.4 ± 6.46% and 11.95 ± 6.23% more efficient than the small-molecule organic glass for pulse height and pulse integral analysis, respectively.