Conceptual study on a novel method for detecting nuclear material using a neutron source

•A new active neutron method using a continuous neutron source is proposed.•The neutron source is moved (rotated) rapidly near the container.•Nuclear material can be detected with rotation speeds of a few thousand rpm.•We developed and fabricated a compact rotation machine rotating neutron sources. This paper presents a conceptual study of a novel active method for detecting nuclear material by using a continuous neutron source. When a container housing nuclear material is irradiated with neutrons, the measurement data recorded by neutron detectors includes both neutrons from the neutron source and those from induced fission reactions. For detecting nuclear material, it is necessary to distinguish the fission neutron component from the source neutron component. The uniqueness of the new method is that it varies the effective intensity of a continuous neutron source by moving it rapidly near the container. As a result of the variation on the effective source intensity, the delay between the moment the source is geometrically closest to the sample and the peaking time of the neutron count rate is detected. This delay is caused mainly by the fission neutron component, that is, the diffusion time of thermalized neutrons, which induce fission reactions in the container, which enables us to detect nuclear material from the measurement data. Because this novel method does not require a D-T tube, which is considerably more expensive than a continuous neutron source, the new system is expected to be affordable and easy to assemble. Moreover, this system can be made so compact that it is suitable for use in mobile applications.