Rad-hard silicon carbide thermal neutron detectors for quality assurance in BNCT

Abstract

Quality Assurance in BNCT dosimetry includes the determination of spatial distributions of thermal neutrons in a water phantom. Activation foils are typically adopted as thermal neutron detectors, making measurements time consuming and requiring considerable manpower. This process would be greatly simplified if an active thermal neutron sensor existed which could scan the volume of a water phantom, as done in conventional radiotherapy with electron LINACs. To this aim, an experiment was organised using rad-hard Silicon Carbide Schottky diodes with active area 1 mm², sensitized to thermal neutrons with a 30 μm ⁶LiF coating. To operate in water, they were made waterproof through a customised 3D printed plastic holder. A suitable neutron field was produced by degrading the 14 MeV beam from the ENEA Frascati Neutron Generator with an assembly formed by a copper-lead shielding followed by a water phantom. The thermal neutron fluence achieved in the water phantom was in the order of 2–3 × 10⁵ cm⁻² s⁻¹. The spatial distribution of thermal neutrons in water was measured using both the Silicon Carbide Schottky diodes and the gold activation foils. The experiment was fully simulated with MCNP. This paper presents the results of the experiment and the possible implications for Quality Assurance in BNCT dosimetry.