Characterisation of radiation fields with combined fast-neutron and
      gamma-ray imaging
Creators: name: Beaumont, Jonathan
Publisher: name: Lancaster University
Year: 2017
Subjects: Neutron imaging
Radiation imaging
Gamma-ray imaging

description: This research explores the use of organic liquid scintillation detectors
      coupled with digital pulse-processing electronics, mechatronics and
      shielding materials to non-destructively characterise radiation sources
      and their emitted radiation fields through passive imaging techniques. The
      research sought to expand upon existing gamma-ray imaging techniques, but
      with focus on fast-neutron imaging techniques which are few in number. 
      
      
      The study involved conceptual design, Monte Carlo optimisation and
      characterisation of collimator and detector geometry, followed by the
      subsequent design and procurement, assembly and modification to produce
      several probe configurations. The full system was then realised through
      control system design, electronic interfacing between custom and
      commercial off-the-shelf components, communication interfacing and
      software engineering to produce the data acquisition systems. Coordination
      with universities and nuclear facilities, logistics and experimental
      planning enabled the successful deployment of imagers at the University of
      Lancaster, University of Manchester, the National Physical Laboratory and
      the Atominstitut at Vienna University of Technology. Data were then
      analysed by custom code, interpreted and benchmarked to conclude the
      accuracy of the output images.
      
      
      Three types of imaging devices were investigated. The first was a
      slot-modulated imaging approach with a tungsten and polythene collimator.
      This imager was the backbone of the study and underwent significant
      developments to allow for deployment in different environments. The
      principle of operation was a heavily shielded single detector which
      sequentially interrogated space through a small unshielded and sensitive
      region over the time-scale of a few hours. The objectives were to create a
      compact, lightweight and portable system which could be used in high-dose
      or highly-shielded environments to image radiation fields. The second was
      a slot-modulated imaging approach with a tungsten anti-collimator,
      effectively using the first imaging system in geometric inversion. As with
      the first imager, this required sequential interrogation of space over the
      order of hours, though here the sensitive region was large. This
      introduced some drawbacks on the image quality but addressed situations
      where a more compact and lightweight probe was required or where neutron
      radiation fields were of very high energy (up to deuterium-tritium fusion
      at 14.1 MeV). The third system was an uncollimated multi-detector system
      which used readings from four detectors with a real-time algorithm to
      determine the position of a single source. This configuration was
      incapable of imaging complex fields, but was effective at tracking the
      position of a single source every 2 seconds. 
      
      
      The bulk of the research was conducted with the slot-modulated imaging
      approach which was demonstrated with the following radiation sources: a
      252Cf source and 241Am/Be source stored in cans, a 252Cf source stored in
      a steel-shielded water tank and a TRIGA test reactor core. These sources
      of neutrons and gamma-rays in combination with variation in shielding
      provided a range of scenarios which were representative of potential
      industrial deployments in nuclear medicine, nuclear safeguards, nuclear
      security and nuclear decommissioning. The anti-collimated imaging
      technique was demonstrated using a 252Cf source stored in a steel-shielded
      water tank. The uncollimated real-time approach was demonstrated in
      tracking a single 137Cs source in 3D space which was representative of
      nuclear security and nuclear medicine applications. The potential
      applications were explored in the context of other technologies in
      previous and active research.