Monte-Carlo simulation of fast neutron detection using double-scatter events in plastic scintillator and Timepix

The Timepix is a semiconductor pixelated detector that measures charge collected in each of its 256×256 pixels (55 μm pitch). Therefore, it is capable of measuring the energy and position of incoming radiation quanta at the same time. We are developing a spectroscopy and radiography technique for fast-neutrons based on the tracking of recoiled protons. The detector combines a Timepix device with a plastic scintillator readout using a silicon photomultiplier (SiPM). Fast neutrons recoil protons from the plastic scintillator. The SiPM records the energy, which protons lose in the scintillator before entering the Timepix. The Timepix then measures the remainder of the proton´s energy and its direction. In case of a setup consisting of a single Timepix and scintillator, the reconstruction of the neutron´s energy requires knowledge of the incoming neutron direction (or the source position); similarly, the incoming neutron energy must be known to reconstruct the direction of the incoming neutron. This paper presents results of Monte-Carlo simulations of a stacked detector that combines two layers of scintillator+Timepix. The stacked arrangement allows recording events when recoiled protons are produced in both the top and bottom scintillators. Such events allow reconstruction of both the incoming neutron energy and direction. Simulated detected proton spectra were compared with experiment and details of the neutron source energy and position reconstruction algorithm are shown.