Improvements in the particle and heavy-ion transport code system (PHITS) for simulating neutron-response functions and detection efficiencies of a liquid organic scintillator

In this study, we simulated the neutron-response functions and detection efficiencies of a liquid organic scintillator using the particle and heavy-ion transport code system (PHITS). We incorporated the algorithm and database of the neutron-response simulation code SCINFUL–QMD into PHITS. Then, we updated the total, elastic, and inelastic cross-section data of the hydrogen and carbon nuclei for neutrons and developed a new scorer to analyze the light outputs from a scintillator. The calculation results of the neutron-response functions and the detection efficiencies were compared with results of SCINFUL–QMD, the previous PHITS with the new scorer, and the reported measurements. It was found that the improved PHITS successfully reproduced the results calculated by SCINFUL–QMD, except for around 150 MeV where a discontinuity in the detection-efficiency curve was observed in the SCINFUL–QMD values. Our results showed better agreement with the measured data than the results of the previous PHITS. The uncertainties of the detection efficiencies calculated by PHITS using the present extensions were estimated to be approximately 15% for neutrons in the energy region below 100 MeV.