Speaker
Description
Neutron detection is an essential technique for precision neutrino detection, in particular, the inverse beta decay reaction of electron anti-neutrino. Super-Kamiokande, a large water Cherenkov detector using 50,000 tons of ultrapure water, has begun a new phase of its operation by dissolving gadolinium into the water (SK-Gd). This leads to significant improvement in neutron detection efficiency and reduction in accidental coincidence background events.
However, discrepancies in neutron detection efficiency between calibration source data and Monte-Carlo simulations have been reported in the early phase of the SK-Gd operation. In this study, we investigated the neutron capture model within the Geant4 simulation toolkit. As a result, it was revealed that the thermal motion of hydrogen atoms in Geant4 was overestimated, leading to an underestimation of the capture cross section of Hydrogen in competition with the other capture nuclei, e.g., Gd. This affects the ratio of capture nuclei, primarily hydrogen and gadolinium, in the SK-Gd.
In this presentation, we will report on the modification of the Geant4 implementation and the results thereof. A series of validations will also be provided, demonstrating the consistency between calculations based on the evaluated nuclear database and the observed data.