Neutron detection gamma ray sensitivity criteria

The shortage of 3He has triggered the search for effective alternative neutron detection technologies for national security and safeguards applications. Any new detection technology must satisfy two basic criteria: (1) it must meet a neutron detection efficiency requirement, and (2) it must be insensitive to gamma-ray interference at a prescribed level, while still meeting the neutron detection requirement. It is the purpose of this paper to define measureable gamma ray sensitivity criteria for neutron detectors. Quantitative requirements are specified for: intrinsic gamma ray detection efficiency and gamma ray absolute rejection. The gamma absolute rejection ratio for neutrons (GARRn) is defined, and it is proposed that the requirement for neutron detection be 0.9<GARRn<1.1 at a 10 mR/h exposure rate. An example of the results from a 3He based neutron detector is provided showing that this technology can meet the stated requirements. Results from tests of some alternative technologies are also reported.