A method for decreasing the loading on scintillation channels in facilities with pulsed neutron sources

Abstract

A method is proposed for decreasing the loading on scintillation channels in nuclear material detection and monitoring facilities comprising pulsed neutron sources, neutron moderators, and scintillators with a system for pulse shape discrimination between neutrons and photons. This method is based on the use of composite scintillators containing cylindrical shells of a thermal-neutron absorbing material. Selecting the sizes of zones in a composite scintillator and the absorber type (cadmium and lithium carbonate with different 6 Li content), it is possible to considerably increase the decay time constant for thermal neutrons in a composite scintillator and thereby reduce its load as compared to a homogeneous scintillator over the same time period after a pulse from the neutron source. The sizes of the scintillator component parts and the absorber material are optimized, which provides a means for decreasing the load on the scintillation channel several-fold while maintaining constant detection efficiency for fast fission neutrons. The capabilities of this method for decreasing the load are demonstrated by the example of the operational prototype of the fissile material detection and monitoring facility with a graphite moderator and LS-13 scintillators. The efficiency of the facility used in this method is compared to that of a facility with a deuterium-containing scintillator, in which no radiative capture photons are produced.