Unveiling secondary particle generation in a SONTRAC detector through GEANT4 simulations

TL;DR

This study uses GEANT4 simulations to analyze secondary particle generation in a SONTRAC detector, revealing proton production, energy spectra, and proton trajectories, which are crucial for solar neutron detection.

Contribution

The paper introduces a detailed simulation of secondary particles in SONTRAC, including proton energy spectra and trajectories, enhancing understanding of detector response to fast neutrons.

Findings

Secondary protons are generated in low numbers (~10^3) compared to incident neutrons.

Proton energy spectra decrease with increasing incident neutron energy.

Many secondary protons stop within the detector, depositing their energy.

Abstract

SOlar Neutron TRACking (SONTRAC) is a detector concept based on a bundle of plastic scintillators by aiming at tracking the solar neutrons through the generation of the secondary particles such as protons from the (n, np) and (n, p) processes. In this study, in addition to the particle population, the energy spectra of the secondary particles including protons, gamma rays, electrons, alphas, and ions that are produced either due to the interaction between the fast neutrons and a SONTRAC detector or through the interplay between the secondary particles and the detector components are determined by means of GEANT4 simulations. The detector geometry in the present study consists of 34$\times$34 Kuraray Y11-200(M) fibers, and the current fiber bundle is irradiated with a planar vertical neutron beam of 0.2$\times$0.2 cm$^{2}$ by using an energy list composed of 20, 40, 60, 80, and 100 MeV where the number of incident neutrons is $10^5$. First, It is revealed that a non-negligible number of secondary protons are generated by the fast neutron bombardment; however, the population of these secondary protons is still low compared to the incident beam, i.e. in the order of $10^3$. Secondly, it is also observed that the energy spectrum of secondary protons exhibits a decreasing trend that is limited by the kinetic energy of incident neutrons. Additionally, the range of the secondary protons along with the deposited energy is computed, and it is demonstrated that a significant portion of the generated protons lose their entire energy and stop within the present SONTRAC detector. Finally, a 34$\times$34 pixel grid detector is introduced on each side of the fiber bundle to collect the optical photons produced from the energy deposition in the scintillation fibers, and the trajectory of the secondary protons on the pixel grid is shown by using a fast neutron beam of 100 MeV.