Chung, Ka Wing (Savanna); (2021) Characterisation of EJ299-33 in RadICAL system and its application. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The radiation weighting factor of neutrons is at least 2.5 times higher than gamma rays, implying that their detrimental effect on biological tissues is 2.5 times worse than that of gamma rays. Secondary neutrons may destroy the merit of the proton therapy- the superior healthy tissue sparing effect. This work studied the feasibility of using the EJ299-33 plastic scintillator system to detect neutrons in a mixed neutron and gamma clinical field due to its portability, clinical friendliness and ultra-short decay time constants. The RadCIAL scintillator system was first exposed to the mixed neutron and gamma field using a proton eye beamline. The result shows that neutron detection using the charge integration method for pulse shape discrimination analysis is possible in a clinical field. It also revealed several limitations of the RadCIAL system, which restricted its applicability outside laboratories. The rest of the thesis focused on optimising and characterising the RadICAL system. The work substantiated the cause of the clipped effect and provided solutions toward peak distortions. Several approaches were developed to correct the clipped effect, investigate other PSD parameters for clipped and attenuated pulses as alternatives to the charge integration method. Using a quasi-monoenergetic neutron beam characterised the neutron energy response function of the RadICAL system. Effects of digitisers’ performance, detector geometry and orientations on the function were investigated. The second minimum from the first derivative of the measured neutron energy spectrum was also studied. This thesis made a step toward developing the RadICAL scintillator system as a neutron detector outside laboratories. However, additional challenges need to be addressed before applying the RadICAL system to measure neutrons in clinics. They include the limited detectable neutron energy range, the system’s insufficient ability to distinguish neutrons from gamma rays due to the EJ299-33 plastic itself and using a high-aspect-ratio shape plastic.

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