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Design and testing of a novel neutron survey meter

Research output: ThesisDoctoral Thesis

Publication date2016
Number of pages211
Awarding Institution
  • Akurugoda Gamage, Kelum Asanga, Supervisor
  • Lancaster University
<mark>Original language</mark>English


This thesis reports on the development of an instrument which can estimate the effective dose of a neutron field, accounting for both direction and energy of the field. This work represents a novel, real-time, approach to workplace directional neutron dosimetry.
A 6Li-loaded scintillator based detector system was developed. This detector system was then used to perform neutron assays at a number of locations in a water phantom. The 6Li-loaded plastic scintillator which was used in this research was sensitive to both gamma and neutron fields. Experimental data were obtained for a number of neutron fields and a comparative analysis of three pulse shape discrimination techniques was performed. A novel technique was identified to perform simultaneous thermal and fast neutron assays using this detector system. The importance of these techniques extends beyond the instrument in this work, and is an important step forward in the identification of a replacement for 3He detectors in neutron detection applications.
The variation in thermal and fast neutron response to different energies and field directions was exploited. The modelled response of the instrument to various neutron fields was used to train an artificial neural network (ANN). Experimental results were obtained for a number of radionuclide source based neutron fields to test the performance of the system. The results of experimental neutron assays at 25 locations in a 20x20x17.5 cm3 water phantom were fed into the trained ANN. A correlation between neutron counting rates in the phantom and neutron fluence rates was experimentally found. The resulting estimates of effective dose rate differed by 45% or less from the calculated dose value, regardless of energy distribution or direction. The ANN was also trained to learn ambient dose equivalent and the resulting ambient dose equivalent rate for the experimental results was found to be 60% or less for the 14 experimental fields investigated. All the experimental measurements were carried out at the low scatter facility at the National Physical Laboratory (NPL), London, UK. It is believed that in the research presented in this thesis, for the first time, a single instrument has been able to estimate effective dose in real-time.
Prior to the work described above, an instrument based on a single loaded liquid scintillator was also studied in this research. By observing the distribution of light collected from a number of neutron captures in a loaded scintillator, an ANN was trained to estimate the effective dose of the field. A number of difficulties must still be overcome to realise this second instrument studied. The primary difficulty being detecting and localising neutron capture within the scintillator.