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BackgroundNeutron localization technology can be used for monitoring spent fuel reprocessing to prevent nuclear criticality accidents.PurposeThis study aims to investigate the effects of different neutron emission modes, 3He pressure, tube diameter, and moderators on the position resolution and detection efficiency of a position-sensitive 3He proportional counter.MethodsFirstly, a 3He proportional counter with a tube diameter, tube length, and 3He pressure of 2.54 cm, 80 cm, and 405 300 Pa, respectively, was taken as object of study, and the Monte Carlo (MC) algorithm was employed to simulate the effects of neutrons with different energies, neutron emission modes, 3He pressures, tube diameters, and moderating bodies on the position resolution and detection efficiency of a position-sensitive 3He proportional counter. Then, the effects of the time difference of arrival (TDOA) on the location of a source in an active zone, source to tube distances, thickness of moderating body, and position resolution of the 3He proportional counter were investigated. Finally, a linear fitting analysis of the active region was performed, and the locations of inactive regions were estimated to determine the positioning ability of the 3He tube.ResultsSimulation results show that the position resolution of this 3He proportional counter is equal in all axial sections, and the position-resolution limit of thermal neutron source is 0.17 cm. When the thickness of the moderating body is 5 cm, and the 244Cm source is close to the external wall of the moderating body, the neutron detection efficiency is 3.0%, and the theoretical position resolution is 9.25 cm whilst experimental result of position resolution is 18.50 cm, half of the theoretical value, and the location resolution limit is 2.64 cm after processed by the linear fitting curve of the active location and a time-difference crest.ConclusionsMC simulation and experimental tests show that the position-sensitive 3He proportional counter exhibits better position resolution and detection efficiency for the 244Cm source when the thickness of the moderating body is 2~3 cm, hence suitable for practical applications.

BackgroundThe use of neutron-based methods to locate radioactive sources within sealed containers holds great practical significance.PurposeThis study aims to locate an AmLi source within the detection space of four position-sensitive neutron detectors.MethodsFirst of all, the Monte Carlo method was applied to designing the moderating shield of the detector. Then, a delay circuit was added to one end of the detector hence the position coordinate of the source y-axis (detector axis) was determined according to the time difference between the two ends of the detector to detect the source neutron signal, and the axial position function of each detector was calibrated. Finally, the detector was used to build a measurement space around sealed container, and the position coordinates of the x-axis and z-axis (the other two directions) were determined by the ratio of the neutron count rate of the two adjacent detectors, so was the function calibration. During the measurement of neutron point-source 3D coordinates, the detector with the largest count rate was first selected to determine the axial coordinates of the source, and then the coordinates of the other two directions of the source were determined according to the ratio of the count rate of the two adjacent detectors to the detector, so as to realize the location of the source.ResultsMeasurement results of five different positions of the point source in the detection space show that the positioning deviation on each coordinate axis is within 1.5 cm, and the relative standard deviation of neutrons measured in this detection space is within 1%.ConclusionsThis methodology effectively demonstrated the feasibility of employing neutron position-sensitive detectors to precisely locate radioactive sources, establishing a strong foundation for future endeavors aimed at accurately determining the positions of nuclear materials within processing equipment in nuclear facilities.