| A fast-neutron method for detecting concealed nitrogen-based explosives in passenger luggage using isotopic sources is presented. The technique utilizes the energy spectrum of transmitted neutrons for identification purposes. Material classification as explosives and non-explosives is accomplished with the aid of interpretation methods; namely, threshold-value method, density-related discrimination and pattern recognition techniques.;Monte Carlo simulations as well as laboratory experiments are utilized to demonstrate the feasibility of the discrimination methods. Two isotopic neutron sources with wide energy spectra, namely, californium-252 and americium/beryllium, are employed. Transmission spectra are measured using a helium-3 detector, a proton recoil counter and scintillator. Various source-detector arrangements are examined to determine the most effective combination suitable for substance identification. A variety of objects are used for testing the interpretation methods.;The segregation of explosives from innocuous objects was successfully exhibited by all identification methods using a number of channels in the spectrum. The results indicate that the use of a californium-252 in conjunction with a helium-3 detector as an appropriate combination among those examined. The simplicity and cost-effectiveness of the developed system should facilitate its installation in small airports or industrial facilities. |
