Development Of Delayed Gamma-ray Spectroscopy For Nuclear Safeguards (4): Integrated Neutron Detection Systems

The Integrated Support Center for Nuclear Nonproliferation and Nuclear Security (ISCN) of the Japan Atomic Energy Agency (JAEA) is developing Delayed Gamma-ray Spectroscopy (DGS) for safeguards. Our earlier experimental results show that delayed gamma-ray spectra can be used to estimate fissile mass using neutron source normalization. As such, the JAEA/ISCN is developing a compact DGS instrument that will incorporate a neutron detection system of multiple neutron monitors to improve the accuracy of mass evaluation. Specifically, the JAEA/ISCN is investigating 3He and 4He neutron detectors for both thermal and fast neutron evaluations. Constrained by the compactness requirement, the detectors’ response for short source distances have been studied. This paper will introduce the scope of neutron detection system followed by a description of the detector characteristics and response at short source distances, including that related to our demonstration irradiator. Finally, preliminary integrated neutron detection systems within a compact DGS instrument will be discussed.