Material classification by fast neutron scattering

The scattering of a beam of fast monoenergetic neutrons is used to determin e elemental compositions of bulk samples (0.20.8 kg) of materials composed from one or more of the elements H, C, N, O, Al, S, Fe and Pb. Scattered ne utrons are detected by liquid scintillators placed at forward and at backwa rd angles. Different elements are identified by their characteristic scatte ring signatures derived either from a combination of time-of-flight and pul se height measurements. or from pulse height measurements alone. Scattering signatures measured for multi-element samples are analysed to determine at om fractions for H, C, N, O and other elements in the sample. Atom fraction s determined from scattering signatures are insensitive to neutron interact ions in material surrounding the scattering sample, provided the amount of material is not excessive. The atom fraction data are used to classify scat tering material into categories including "explosives", "illicit drugs" and "other materials" for the purpose of contraband detection. (C) 2001 Elsevi er Science B.V. All rights reserved.