Characterization of 241AmBe neutron source with He-based multi-shell neutron spectrometer

Abstract

The neutron spectrum of an Americium-241 Beryllium (²⁴¹AmBe) source while it is in a moderated container was determined using the He-based multi-shell neutron spectrometer (He-MuNS). The MuNS consists of high-density polyethylene (HDPE) spherical shells that are assembled to form Bonner spheres with 10 different diameters. For this study we used only five configurations of the He-MuNS.  The ³He detector is used to detect thermal neutrons, which were then counted using a Ludlum scaler ratemeter. The measured values from MuNS were used as inputs in the FRUIT code to unfold the neutron spectrum and obtain dose equivalents. The obtained spectrum from the moderated ²⁴¹AmBe shows that the fast neutron peaks have shifted by 1.04 orders of magnitude compared with the bare source spectrum. This confirms the moderating effect of the source container. Emitted fast neutrons of ²⁴¹AmBe cover the energy range from 1.03-16.4 MeV. The ambient dose equivalent that was derived is 0.546 µSv/h. Results of this work were used as basis for radiation protection measures in handling the source to prevent unnecessary exposure of workers to neutron radiation.