Fast Neutron Detectors for Imaging Applications

In parallel to the D-D fusion fast neutron generator development at the Paul Scherrer Institute (PSI), fast neutron detectors for imaging applications are being developed at PSI and ETH. These detectors are based on plastic scintillators and Silicon Photomultipliers (SiPM). When a fast neutron elastically scatters with hydrogen in a plastic scintillator, the energy of the recoil hydrogen nucleus excites the molecules in the plastic, which subsequently dexcite through light emission. This light is detected by the SiPM, which internally amplifies the signal, and registers a counted neutron.

An array of these detectors can function as a 1D radiography system. By rotating the subject from 0 to 360 degrees incrementally, and measuring a 1D radiogram at each projection angle, a 2D cross-section of the object can be calculated using tomographic image reconstruction techniques.

A schematic of such a setup is indicated below, with source, subject, and detector arc. Below the schematic, a simulated reconstructed tomogram is shown next to the subject cross-section modelled. This imaging system is currently in the process of being realized, and there are plans to apply it to industrial multi-phase flow scenarios, such as steam-water flow in a boiling water reactor.