A quenching factor measurement for BGO scintillators

BGO scintillator is widely used in particle physics experiments. It is also used in Super-Kamiokande to evaluate the efficiency of neutron tagging which can select electron antineutrino events via inverse beta decay process. A relative 10% discrepancy between the measured and simulated efficiency of neutron tagging was reported as systematic errors. A precise measurement of responses of the BGO scintillator to neutrons would suppress this systematic uncertainty. We carried out a neutron beam test at AIST, Japan to measure neutron scattering in BGO detectors. The data of elastic scattering with neutron and nuclei in BGO crystal are stored when signals are observed by both BGO and liquid scintillator detectors at the same time. Background events of gamma rays are suppressed by the pulse shape discrimination method in liquid scintillation detector. A visible energy of nuclear recoil tends to be smaller than the original energy. The ratio of visible energy to recoil energy is defined as quenching factor. Varying the scattering angle, the quenching factor as a function of the recoil energy has been measured. In this presentation, we will report the result and detail of analysis.