Security Applications of Novel Neutron Sources

The smuggling of illicit goods poses a significant threat to the safety, security and economy of all nations. Undeclared black market goods, illegal narcotics and weapons are all threats that could ideally be prevented from crossing national borders. At present cargo interrogation is primarily performed using X-rays, which can be defeated by effective shielding and disguising of objects. Neutron interrogation offers an additional line of defence against smuggling, and there are a number of techniques available, which are discussed in this thesis.
In this thesis a review of the limitations of current cargo interrogation technology is given. Current technology has limitations, and these are considered. In preparation of this thesis Monte-Carlo transport codes MCNPX and Geant4 were used as well as nuclear inventory code EASY-II, and a description of their key features is given.
The possible methods of interrogating cargo with neutrons is discussed. Cargo can be interrogated with a range of neutron spectra, and either the neutrons or the produced gammas can be used. The use of techniques based on detecting neutrons or gammas is discussed, and simulations of gamma production by fast inelastic neutron scattering are presented. This is followed by a review of the principles of compound nucleus based neutron sources. The produced neutron spectra and the decay isotopes are both important considerations, and the results of possible combinations of target and projectile are given.
Use of deuterons to produce neutrons through compound nucleus reactions has potential, due to the high Q of some reactions. If deuterons are used there is also a possibility of dissociation, if kinetic energies above the binding energy are used. At present deuteron dissociation cannot be simulated in Geant4 or MCNPX. Two new models of deuteron dissociation, one high and one low precision, have been developed for inclusion in Geant4. The physics and operation of these models is discussed and comparison with experimental data is presented.
When interrogating cargo with neutrons it is unavoidable that some level of activation will occur. In particular the activation of food is of significant concern due to the exposure caused by ingestion. To date there has been little investigation of the activation of cargo under neutron interrogation. By using up to date nuclear data libraries and numerical techniques it was possible to extend early work in this field.
In addition it is claimed in literature that 24N a is the only isotope of concern, this is shown to only be valid for certain combinations of food composition and irradiating energy.