Neutron control by inorganic scintillators for detection systems of fissionable radioactive substances

Full text : Comparative measurements and analysis of detection efficiency of fast neutrons from 239 Pu-Be source have been carried out in a broad energy range En ≅ 0.1 * 10 MeV using oxide scintillators Bi4Ge3O12, Gd2SiO5, CdWO4, ZnWO4, ZnSe (Te,O), as well as 6 LiI (Eu). Detection efficiency of fast neutrons by heavy oxide scintillators was found to be very high (≅ 40-50 percent). The neutron inelastic scattering reaction is considered as the most probable interaction mechanism of neutrons with nuclei of heavy oxide scintillators. It is concluded that heavy oxide scintillators, which are at the same time efficient gamma-detectors, allow creation of a highly efficient gamma-neutron detector ensuring high detection efficiency of fissionable radioactive substances. Experimental results obtained in this work confirm the correlation between large gamma-quanta excitation cross-sections in reaction and cross-sections of inelastic scattering of fast neutrons. These results show a possibility of obtaining high efficiency (up to ≅ 50-60 percent) of detection of fast neutrons by heavy oxide scintillators Bi4Ge3O12, Gd2SiO5, CdWO4, ZnWO4, ZnSe (Te,O). Comparative analysis of experimental and theoretical data on fast neutron detection efficiency by such scintillators in a broad energy range En ≅ 1 * 10 MeV on atom nuclei have shown that the most probable mechanism of interaction of neutrons with nuclei of the scintillator material is the reaction of inelastic scattering of neutrons. The use of inelastic neutron scattering reaction on nuclei of heavy oxide scintillators allows creation of a high efficiency detector of mixed gamma-neutron fluxes, in which the energy of fast neutrons is directly, without intermediary media, converted into energy of gamma-quanta. This can lead to substantial (by several times) increase in sensitivity of systems for detection of fissionable radioactive substances, accompanied by a reduction in their cost.