Year
2005
Abstract
The detection of shielded highly enriched uranium is a challenging problem that is being addressed by numerous researchers. Ports of entry require fast, accurate measurement systems that provide simple read-out responses. A number of currently proposed techniques use photon sources to induce fission in the nuclear material, and to detect the subsequent gamma rays and neutrons from fission. The design of such devices and the analysis of the measurement results rely on Monte Carlo codes to simulate the interaction of neutrons and photons with the nuclear material, the shielding, and the radiation detectors. However, current Monte Carlo codes cannot accurately simulate the emission of correlated particles from photofission. Handling multiplicities and spectra of the whole photofission yield is vital for implementing efficient new techniques capable of identifying nuclear materials and estimating their amount. The goal of this study is to provide a tool that addresses and solves these deficiencies. Methodologies that rely on the acquisition of correlated signals from prompt and delayed neutrons and photons emitted whenever a photofission event takes place are being investigated. The sensitivity and efficiency of organic scintillators for measuring the signals from impinging fast neutrons and photons is also being investigated. In this paper, the photofission simulation currently implemented in MCNPX is being described and an extension to improve the simulation of secondary particles is being proposed. Our approach is based on the use of two existing and well-benchmarked codes, MCNPX and MCNP-PoliMi. The application of the proposed method to determine the presence of nuclear material in luggage transported on a conveyor belt is also being presented.