Year
2002
Abstract
The physical method of fissile materials (FM) detection, developed in the first year of the ISTC project ? 596, demonstrated that it is possible to detect 8 g of 235U in passengers’ luggage in 5 seconds using a pulsed DT source. For this case it is impossible to conceal FM with lead shields. As the proposed model of control system functions using thermal neutrons, it is possible to conceal FM with shields having high thermal neutron absorption cross-section. Calculations performed using the MCNP-4a code have shown that 70-90 µs after a neutron pulse of the neutron generator there are still epicadmium neutrons existing in the system with hydrogencontaining moderators. The goal of the experiments was to separate neutrons and photons and to detect fission neutrons in a specified time interval. The experiments have shown, that at a neutron pulse frequency of 30-60 Hz this task is not resolved due to overload on spectrometers. Analysis of the existing methods of separation of neutrons and photons has shown that this task is basically resolved using a digital technique of separation of various types of particles in scintillators. Each scintillation pulse from a neutron (recoil proton) or photon (electron) can be digitally represented and then identified using a specially created code. In this case the interfering pulses can quite easily be removed during the mathematical processing of scintillation responses of neutrons and photons. The created code and experiments performed have demonstrated the possibility of digital separation of neutrons and photons in stilbene, NE-213 and LS-13. An alternative to use digital technology for the specified task is to create an installation that uses coincidences of fission neutrons and photons. A model of that system with a DD neutron generator and corresponding code has been created. Experiments on the model have shown the fundamental possibility to detect 120 g of 235U in 5 seconds at a neutron yield of ~108 n/s from a pulsed neutron generator.