Thermal neutron detection at outer electrode surfaces of composite polycrystalline B, BN, B 4C and LiF through air ionization

Abstract

Single phase polycrystalline hexagonal boron nitride (BN) or mixed with boron carbide (B x C) and/or polycrystalline cubic lithium fluoride (LiF) can be embedded in an insulating polymeric matrix. This matrix acts as a binder forming a composite material. Such materials were tested as surface neutron converters of gaseous detectors. Signals were induced by ionized air near electrodes. The detectors show a rather good spectral response for ionized air produced by alpha particles emitted from a 241Am (5.5 MeV) isotope source (∼10 5 cm −2 s −1) as well as low gamma sensitivity. For detection of thermal neutrons from a low flux source (∼200 cm −2 s −1), neutron counting is possible by subtracting the integrated noise from the integrated total signal counted above some threshold; here again the signals are produced by the ionized air and cannot be detected in vacuum.