Investigation of Machine Learning for Countermeasure of Radioactive Material Smuggling
Year: 2015

In this paper, we present as a viable alternative for countermeasure of radioactive material smuggling, an advanced computational model to implement computer automation for dual energy X ray imaging technique to detect and recognize nuclear and radiological material smuggled in cargo containers. Successful computer automation enables the dual energy X ray imaging technique to efficiently sense and recognize radiological and/or nuclear materials, especially shielded Highly Enriched Uranium (HEU) with high detection accuracy, a low positive false alarm rate, and negligible impact on freight movement. Thus, dual energy X ray inspection can feasibly be used to efficiently inspect 100% of cargo containers entering the US. We will begin with detail description of the dual energy X ray method and then go through machine leaning algorithms for detecting radioactive materials. Two machine learning approaches are considered in the paper: data mining and pattern classification. Future research effort to study the solutions will also be presented in the paper. Our goal is to develop machine learning techniques to improve detection accuracy while reducing the excessive inspection times that are presently obstructing full deployment of active inspection systems such as the dual energy X ray machine. 1. Dual energy X ray method 1 1 X ray attenuation A beam of X ray may interact with matter via three primary physic mechanisms: photoelectric effect, Campton scattering, and pair production. All these three X ray matter interactions result in X ray attenuation. In the photoelectric effect, the photons of the X ray eject the electrons from matter if the photon energy is greater than the work function of the matter. Compton scattering is another type of interaction that X rays undergo energy loss in matter. This inelastic scattering of photons in matter results in a decrease in energy of an X ray photon. Part of the energy of the X ray photon is transferred to a scattering electron, which recoils and is ejected from its atom, and the rest of the energy is taken by the 2015 METRANS International Urban Freight Conference, October 21 23, 2015. Long Beach, CA, USA scattered photon. In nuclear physics, when an X ray photon interacts in the vicinity of a nucleus, it is possible to produce a pair of electron and positron; this process is referred to as pair production. In this case, the photon energy of the X ray will be at least total rest mass energy of the two particles. The pair production also leads to an energy loss in X ray.  X ray attenuation is essentially dependent on the X ray photon energy and the atomic number of the element. The photoelectric effect is predominant factor attributed to the low energy X ray (less than 0.5 MeV) attenuation for the substance that has large atomic number. However, Compton scattering is a main attribute of the attenuation for the substance of small atomic number within the same energy range, as shown in Fig. 1. Moreover, Compton scattering is a major attribute to the X ray attenuation between 0.5 and 5.0 MeV energy range disregarding the atomic number of the substance. For high energy X ray photons of above 5.0 MeV, pair production becomes a major attribute of the X ray attenuation. A narrow beam of monochrome X ray with an incident intensity Ii, penetrates a layer of material with thickness t and density emerges with intensity Io expressed as in