title: A silicon-based detection system for secondary neutron measurements in particle therapy
Creators: name: Alsulimane, Mohammad
Publisher: name: University of Liverpool Repository
Year: 2025

description: Neutron detection is becoming of prime importance worldwide for radiation protection due to the recent technological development in medical and industrial fields, such as accelerators and nuclear reactors, which are regularly associated with neutron hazards. These neutrons require monitoring because of their biological effect, however, monitoring neutrons is challenging to detect. Furthermore, it is difficult to discriminate them in a mixture of radiation sources. Therefore, neutron assessment is an active area of research for radiation protection purposes.
The work developed in this project presents a silicon-based neutron detection system with high γ-ray discrimination for monitoring and distinguishing the thermal neutron signals in mixed radiation environments. This work covers simulations, design, fabrication, characterisation, and application of the system, focusing on three main objectives. Firstly, it investigates neutron production during charged particle therapy. Although the most significant particle therapy advantage is the radiation dose distribution compared to radiotherapy, secondary neutrons are produced as a result of particle interactions with the water molecules and along the beam directions following the nuclear interaction phenomenon. A water phantom tracking system has been developed to monitor the primary beams and their interactions within the phantom using Geant4. It founds that neutron intensities are proportional to the particle type and their kinetic energies, where the neutron production ratio reaches up to 0.04 and 0.84 per primary particle of proton and carbon-ion, respectively. The neutron equivalent dose can reach up to 5.4 and 63.13 mSv/1.0 Gy of proton and carbon-ion, respectively.
Secondly, a silicon-based neutron detection system is developed, where the system is modelled using Geant4 and then constructed, calibrated and evaluated in the University of Liverpool laboratories. The system allows operating at a high LLD setting to remove the unwanted signals while keeping the neutron signals due to the Q-value of the recoil radioactive products of 6LiF equal to 4.78 MeV. Therefore, neutron signals can be easily distinguished with a high gamma rejection ratio. The detection system is examined in two configurations: single and sandwich configurations. The detection efficiency can reach up to 6.3% and 11% for the single and sandwich configurations, respectively. In addition, the efficiency can improve if the system is connected in a stack, where the efficiency can be raised to 33% and 56% for both stacks in single and sandwich configurations, respectively. Several designs of silicon diodes are fabricated with a thin coating of 6LiF, with thicknesses ranging between 0.6 and 10.0 μm. These diodes are examined in front of an AmBe source. The experimental detection efficiency ranged between 0.4% to 2.5%. Subsequently, the experimental measurements were modelled for validation purposes, where there is an agreement between the experimental and simulation results. The last objective involves examining the system performance in a pencil proton therapy unit to assess its ability to discriminate neutrons from other radiations.