Directional stand-off detection of fast neutrons and gammas using angular scattering distributions

Abstract

Abstract-We have investigated the response of a Double Scatter Neutron Spectrometer (DSNS) for sources at long distances (>200 meters). We find that an alternative method for analyzing double scatter data avoids some uncertainties introduced by amplitude measurements in plastic scintillators. Time of flight is used to discriminate between gamma and neutron events, and the kinematic distributions of scattering angles are assumed to apply. Non-relativistic neutrons are most likely to scatter at 45°, while gammas with energies greater than 2 MeV are most likely to be forward scattered. The distribution of scattering angles of fission neutrons arriving from a distant point source generates a 45° cone, which can be back-projected to give the source direction. At the same time, the distribution of Compton-scattered gammas has a maximum in the forward direction, and can be made narrower by selecting events that deposit minimal energy in the first scattering event. We have further determined that the shape of spontaneous fission neutron spectra at ranges >110 m is still significantly different from the cosmic ray background.

Performance study of a directional fast neutron detection system based on TPC and plastic scintillation detectors

“…where is the angle between and ', and (0, , ) is the Gaussian distribution of . Equation (7) has no analytical solution due to the integral of the Gaussian function, but the angular resolution of the SBP image can be determined from the ARM as the following equation using numeral calculations: FWHM SBP ≅ 3.74 (8) The angular resolution of the SBP image is estimated to be 7.1° using Equation (8) and the estimation result of the ARM in Section 3.1, which is in good agreement with the experimental result.…”

Directional fast neutron detection using a time projection chamber and plastic scintillation detectors

“…1). In the past decade, two types of detector systems have been designed for fast neutron scatter imaging and are namely the neutron scatter camera [1][2] , and the neutron time projection chamber (TPC) [3][4] . The neutron scatter camera detects the direction of the fast neutrons based on a method similar to Compton imaging of γ-rays ( Fig.…”

Directional fast neutron detection using a time projection chamber

“…These include Time Projection Chambers (TPCs) filled with H 2 [2,3], 3 He gas [4], or a mixture of gases [5]. Considerable progress has also been made in adapting organic scintillator multiple proton recoil imagers designed for solar neutron imaging [6] to the lower energies typical of fission neutron sources [7,8,9].…”