A measurement of the time profile of scintillation induced by low energy gamma-rays in liquid xenon with the XMASS-I detector

摘要

We report the measurement of the emission time profile of scintillation from gamma-ray induced events in the XMASS-I 832 kg liquid xenon scintillation detector. Decay time constant was derived from a comparison of scintillation photon timing distributions between the observed data and simulated samples in order to take into account optical processes such as absorption and scattering in liquid xenon. Calibration data of radioactive sources, ~(55)Fe, ~(241)Am, and ~(57)Co were used to obtain the decay time constant. Assuming two decay components, τ_1 and τ_2, the decay time constant τ_2 increased from 27.9 ns to 37.0 ns as the gamma-ray energy increased from 5.9 keV to 122 keV. The accuracy of the measurement was better than 1.5 ns at all energy levels. A fast decay component with τ_1 ～ 2 ns was necessary to reproduce data. Energy dependencies of τ_2 and the fraction of the fast decay component were studied as a function of the kinetic energy of electrons induced by gamma-rays. The obtained data almost reproduced previously reported results and extended them to the lower energy region relevant to direct dark matter searches.