Application of Fast Neutron Associated Alpha Particle Method in Explosives Inspection

Abstract

The explosives inspection technique on the base of the associated α-particle imaging method(API) can effectively detect hidden explosives. The key feature of the API method is the measurement of the time difference between detection of α particle and γ quantum. It provides the possibility to determine the distance traveled by the neutron before it is inelastically scattered by the nuclei of the interrogated object. So it can determine a gamma-spectrum from the definite localized region in the object. By this method, a package of explosive neutron device was designed. The device was composed of the sealed tube neutron generator (NG) with α particle detection function, LYSO γ detector, data analysis system. LYSO detector’s efficiency and energy response about 4439 keV and 5103 keV γ ray were calculated by Monte Carlo method, which had good agreement with the experiment datas. By comparison experiments on the graphite sample using API method with direct measurement method about fast neutron inelastic scattering, the API method could effectively inhibit high gamma ray interference signals that producted by the fast neutron interact with the surrounding environment,its total energy peak and single escape peak could be recognized easily. Through the experimental measurement of graphite, water, three melamine and other samples, the relatively pure spectrum of C, N, O elements were obtained. At the same time ,the experimatal datas spectrum about washing powder, milk powder and other chemicals placed together with TNT, ammonium nitrate samples were tested. A large signal-to-background ratio provided by the API method significantly facilitated the determination of C, N, O elements content and the identification of the hidden substances, which provided the basis for accurate identification of explosives.

Keywords

• monte carlo simulation associated α-particle method inspection of explosives