Urszula Wiącek

Detection of explosives and other illicit materials by a single nanosecond neutron pulses — Monte Carlo simulation of the detection process

Recent progress in the development of a Nanosecond Impulse Neutron Investigation System (NINIS) intended for interrogation of hidden objects (explosives and other illicit materials) by means of measuring elastically and non-elastically scattered neutrons is presented. The method uses very bright neutron pulses having durations of the order of few nanoseconds, generated by a dense plasma focus (DPF) devices filled with pure deuterium or a deuterium-tritium mixture as a working gas. A very short duration of the neutron pulse, as well as its high brightness and mono-chromaticity allows using time-of-flight methods with bases of about few meters to distinguish signals from neutrons scattered by different elements.Results of the Monte Carlo simulations of the scattered neutron field from several compounds (explosives and everyday use materials) are presented. The MCNP5 code has been used to get information on the angular and energy distributions of neutrons scattered by the above mentioned compounds assuming the initial neutron energies to be equal to 2.45 MeV (DD) and 14 MeV (DT). A new input has been elaborated that allows modeling not only a spectrum of the neutrons scattered at different angles but also their time history from the moment of generation up to the detection. Such an approach allows getting approximate signals registered by hypothetic scintillator + photomultipler probes placed at various distances from the scattering object, demonstrating principal capability of the method to identify an elemental content of the inspected objects. The extensive computations reveled also several limitations of the proposed method, namely: low number of neutrons reaching detector system, distortions and interferences of scattered neutron signals etc.Further more, preliminary results of the MCNP modeling of the hidden fissile materials detection process are presented.

Amplitude degradation of thin layer in neutron logging

The paper presents an analysis and discussion of the problem of underestimation of neutron signal amplitude in profiling of the thin-layers rock media. The corresponding neutron profiles were modeled using the Monte Carlo method, and the formalism of the general neutron parameter GNP was used to analyze the results. We show that the degradation of the thin layer signal amplitude depends on the layer thickness, and on the difference in the neutron properties of the layer and its surrounding medium.