Efficiency Studies of Fast Neutron Tracking using MCNP

Abstract: Fast neutron identification and spectroscopy is of great interest to nuclear physics experiments. Using the neutron elastic scattering, the fast neutron momentum can be measured. (Wang and Morris, 2013) introduced the theoretical concept that the initial fast neutron momentum can be derived from up to three consecutive elastic collisions between the neutron and the target, including the information of two consecutive recoil ion tracks and the vertex position of the third collision or two consecutive elastic collisions with the timing information. Here we also include the additional possibility of measuring the deposited energies from the recoil ions. In this paper, we simulate the neutron elastic scattering using the Monte Carlo N-Particle Transport Code (MCNP) and study the corresponding neutron detection and tracking efficiency. The corresponding efficiency and the scattering distances are simulated with different target materials, especially natural silicon (92.23$\%$ $^{28}$Si, 4.67$\%$ $^{29}$Si, and 3.1$\%$ $^{30}$Si) and helium-4 ($^4$He). The timing of collision and the recoil ion energy are also investigated, which are important characters for the detector design. We also calculate the ion travelling range for different energies using the software, "The Stopping and Range of Ions in Matter (SRIM)", showing that the ion track can be most conveniently observed in $^4$He unless sub-micron spatial resolution can be obtained in silicon.