What is a breakdown of continuous component hidden under 4.4-MeV gamma-ray peak from the AmBe source?

Abstract

Americium-Beryllium (AmBe) is a typical source to be use for a calibration of neutron detection efficiency in underground astroparticle physics experiments. It has been considered to emit a neutron and a 4.4 MeV gamma ray simultaneously, which allows us to select events with a neutron by tagging the 4.4 MeV gamma-ray signal. This time, we focus on the component of high energy tail above 4.4 MeV peak in a deposited energy distribution, under the measurement with inorganic scintillators. In neutron tagging technique with AmBe surrounded by BGO for gamma tagging, there is a possibility of underestimating the tagging efficiency when there are neutrons stopped at BGO. We aim to understand the breakdown of component of the high energy tail from AmBe to contribute reduction of a systematic uncertainty related to the neutron detection efficiency for the astroparticle physics. We will present a result of measurements for neutrons and gamma rays using NaI(Tl) and liquid scintillation detectors.