Ph.d. degree
Lund University, Sweden, 2023

Nicholai Mauritzson

Supervisor: Kevin Fissum

Neutron-Induced Scintillation in Organics

Keywords:

• liquid organic scintillator
• neutron tagging
• light yield
• simulation

Abstract:

Neutrons are widely used as probes of matter to study materials in a broad range of fields from physics, chemistry and medicine to material sciences. Any application utilizing neutrons needs to employ a well-understood and optimized neutron-detector system.

This thesis is centered on fundamental aspects of neutron-detector development, including the establishment of the Source Testing Facility at Lund University, experimental methods for the in-depth characterization of scintillator-based neutron detectors and analytical and computational methods for the precise interpretation of results. It focuses on the response of liquid organic scintillators to fast-neutron and gamma-ray irradiations, specifically for NE213A, EJ305, EJ331 and EJ321P. A simulation-based method for detector calibration was developed which allowed for the use of polyenergetic gamma-ray sources in this low energy-resolution environment. With an actinide/beryllium neutron source and a time-of-flight setup, beams of energy-tagged neutrons were used to study the energy-dependent behaviour of the intrinsic pulse-shape of NE213A and EJ305 scintillators.

The results demonstrated the advantages of the neutron-tagging method and how the combination of neutron tagging and pulse-shape discrimination can give deeper insight into backgrounds resulting from inelastic neutron scattering. A comprehensive characterization of the neutron scintillation-light yield for NE213A, EJ305, EJ331 and EJ321P was also performed. It employed the simulation-based calibrations to confirm existing light-yield parametrizations for NE213A and EJ305, and resulted in light-yield parametrizations for EJ331 and EJ321P extracted for the first time from data.

In addition to the development of a simulation-based framework for the study of neutron-induced scintillation in organic scintillators, the methods and results presented in this thesis lay the foundation for future source-based neutron-tagging efforts and scintillator-detector research and development.