Characteristic photon yields from thermal neutron activation of explosives for a portable detection system

Abstract

Explosive detection systems (EDS) based on thermal neutron activation can be used for detection and identification of concealed explosives such as trinitrotoluene, cyclonite, and ammonium nitrate (NH 4 NO 3 ). Activation results in emission of characteristic gamma rays of constituents whose relative intensities yield atomic fractions of the explosives and instant identification. Applications of EDS can also be at airports and seaports as well as in vehicles. Such systems have been studied, developed and tested and are being refined in their design and functionality as several issues still need to be resolved, such as the associated high radiation dose and development of fast algorithms for their identification. This paper considers a portable EDS, incorporating a neutron source and radiation detection systems, which can fit into a portable briefcase of dimensions 40 cm × 30 cm × 8 cm. The detection efficiency and radiation dose are computed by carrying out simulations, to estimate the strengths of characteristic photon yields, using the Monte Carlo code MCNP5 to present a useful and efficient engineering design. Two factors of concern were found to be the excessive photons from material of least interest ( 10 B, Ca, Pb) and the excessive radiation dose in the immediate vicinity of a portable system. However, an accurate estimate of the H/N ratio was obtained with simulation carried out for ~1kg concealed TNT explosive. The ratio was found to be ~1.61 which is very close to the actual ratio (1.67). Thus, the accurate identification of TNT explosives can be efficiently carried out by such a portable system.