A neutron scatter imaging technique with distance determining capability

Abstract

Conventionally, a neutron scatter camera was used to determine the direction of neutron sources. Therefore, various investigations have been conducted on the design of cameras and imaging algorithms. However, the source distance cannot be determined using the existing neutron cameras. In this study, inspired by binocular vision, an approach was proposed to locate the neutron source (both direction and distance) based on a neutron scatter camera composed of two imagers. Each imager reconstructed an image. The source distance was estimated by comparing the two images. An intersection-based back projection imaging (IBPI) method is proposed to suppress the appearance of fake high-luminosity regions in conventional back-projection imaging (CBPI). An imager with four liquid scintillator detectors (one front and three back) was constructed to test the locating approach at the State Nuclear Security Technology Center (SNSTC). A 252Cf isotope source of 3.0×107 Bq was employed as the neutron source in the experiment. Gamma rays and neutrons were discriminated using the pulse shape discrimination (PSD) method. The angular resolution in the experiment was improved from 25° to 13° using IBPI . The binocular distance measurement (BDM) method was successfully applied to estimate the source distance. The experimental results indicate that the source distance is determined more unambiguously using IBPI+BDM than CBPI+BDM. A Monte Carlo simulation was also performed to investigate the design of such a scatter imaging system of the neutron. A relatively large separation between the two imagers was crucial for estimating the source distance. When changing the separation between the two imagers from 40 to 160 cm, FWHM of the estimated source distance could be improved from 9.5 to 4.1 cm.