Light in plastic, it's fantastic: a new fast neutron spectrometer with EJ-276 plastic scintillator and silicon photomultipliers in a novel geometry

Kidson, Miles Brower

Light in plastic, it's fantastic: a new fast neutron spectrometer with EJ-276 plastic scintillator and silicon photomultipliers in a novel geometry

Thesis / Dissertation

2025

Publisher

University of Cape Town

Department

Department of Physics

Faculty

Faculty of Science

Abstract

Fast neutron fields are present in aviation, space, radiotherapy, and nuclear research environments. Characterisation and continuous monitoring are required for risk assessment and workplace dosimetry as neutrons present particular radiation protection challenges. These neutron fields are often coupled with gamma ray fields, cover a large range in energy and intensity, and have variable directional characteristics. Existing techniques rely on systems that are often bulky, unsafe to use outside of laboratory environments, or require complicated operation. A compact detector system has been developed at the University of Cape Town for fast neutron spectrometry and dosimetry based on plastic scintillator, silicon photomultipliers, and digital data acquisition. This work presents the characterisation and calibration of a detector system suitable for neutron measurements up to 20MeV composed of an EJ-276 scintillator machined to a novel spherical geometry, a MicroFC-60035 silicon photomultiplier, and a DT5730 digitiser. Measurements of well-characterised fast neutron fields were made at the n-lab, University of Cape Town, and international fast neutron metrology facilities AMANDE (IRSN, France) and PIAF (PTB, Germany). Detector response functions were measured between 1.0MeV and 16.0MeV using time-of-flight analyses, and simulations of the detector system with Geant4 were used to determine the neutron detection efficiency. Neutron energy spectra of monoenergetic and broad energy neutron fields were unfolded using the efficiency-corrected detector response functions, demonstrating the capabilities of the device as a neutron spectrometer.