Jones, Ashley Richard and Joyce, Malcolm (2016) A novel detection system using neutron/gamma pulse shape discrimination, for use in active interrogation environments. PhD thesis, Lancaster University.
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Abstract
Continuous improvements are being sought to identify special nuclear material more accurately. Active interrogation is a current field of research for this application, capable of penetrating shielding materials but which can feature a complex and challenging radiation field for detectors to operate in. This research was aimed at improving active interrogation techniques further by optimising experimental setups and procedures and reducing undesirable dead periods of acquisition which may be observed. The important outcomes from this research are listed below: • The creation of a new empirical fit to better represent the rising edge of pulses from both neutrons and gamma rays than the currently used Marrone fit (suited to the decay tail of pulses). • The ability to clearly distinguish a selection of gamma rays using this rise time technique post-processing previously acquired data consisting of a mixed radiation field. • The effect of angular orientation of liquid scintillators on FoM values after performing PSD techniques has been identified as well as sensitivity issues associated with the position of the nitrogen void within these detectors. • A novel gated organic plastic scintillator detector has been operated and controlled using a trigger circuit devised in this research. This circuit controlled whether the gated detector was active through the presence of light. • A radiation based detector was integrated with this trigger circuit controlling the gated detector by making the device inactive whenever a radiation count was observed.