Abstract
The emergence of new methodologies with promising applications that could impact nuclear security and emergency preparedness detection systems in the near future motivate the development of computational tools that allow the theoretical investigation of the relevant design parameters for such detection systems. Here, we present Monte Carlo simulations using the MCNP6 code to investigate the use of fast neutron-neutron and gamma-neutron coincidences in addition to conventional methods for detection of special nuclear materials (SNM) using inorganic scintillator detectors. The results show fair agreement between MCNP6 and MCNP-PoliMi simulations for neutron-neutron coincidences and that coincident detection of gamma rays and fast neutrons has a potential for enhancing the sensitivity for detection of SNM compared with conventional gamma-ray, single-neutron, and fast neutron-neutron coincidence detection schemes.
Highlights
Nuclear and radioactive materials outside of regulatory control (MORC) are detected with radiation detection systems, such as Radiation Portal Monitors (RPM)
MCNP6 and MCNP-PoliMi The Monte Carlo code MCNPX-PoliMi is commonly applied for such studies and has been developed from the MCNP code for special use in safeguards experiments that rely on the detection of prompt neutrons and gamma rays from fission [3, 5, 19, 20, 26]
The single neutron and neutron-neutron coincidence count rates for four different PuO2 samples were calculated with MCNP6 and compared with the experimental data and MCNP-PoliMi calculations presented in Ref. [5]
Summary
Nuclear and radioactive materials outside of regulatory control (MORC) are detected with radiation detection systems, such as Radiation Portal Monitors (RPM). Neutron-neutron (nn) coincidence techniques are usually preferred [2, 5, 13,14,15,16,17] as they are subject to low natural background rates, even though the spread in the correlation time for neutrons pairs is larger than for photons, due to the time-of-flight dependence on the neutron energy It has been shown [5] that a multidetector setup based on organic liquid scintillation detectors can be as efficient in detecting SNM as a high-end commercial system based on moderated helium-3 counters [18]. Another promising development is the use of fast gamma-neutron (gn) coincidence correlations between prompt neutrons and gamma rays in the quantification of fissile materials in nuclear safeguards and security applications [19]. Gamma-fast neutron coincidence detection may have a higher sensitivity as well as a higher specificity than fast nn coincidences for the detection of SNM due to high gamma-ray multiplicity and the unique time correlations between the photons and neutrons emitted in fission, respectively [17, 19, 20]
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