Thermal neutron detection at outer electrode surfaces of composite polycrystalline B, BN, B4C and LiF through air ionization

Single phase polycrystalline hexagonal boron nitride (BN) or mixed with boron carbide (BxC) 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 (∼105 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.