Mark S. Rowland

Active Detection of Shielded SNM With 60-keV Neutrons

Fissile materials, e.g., 235U and 239Pu, can be detected non-invasively by active neutron interrogation. A unique characteristic of fissile material exposed to neutrons is the prompt emission of high-energy (E > 1 MeV) fission neutrons. One promising mode of operation subjects the object to a beam of low-energy (E < 1 MeV) neutrons, generated by a proton beam impinging on a Li target. The emergence of high-energy secondary neutrons then clearly indicates the presence of fissile material. Our interrogation system comprises a low-dose 60-keV neutron generator (5 times 106/s ), and a 1 m2 array of scintillators for high-energy neutron detection. Preliminary experimental results demonstrate the detectability of small quantities (376 g) of 235U shielded by steel (200 g/cm2) or plywood (30 g/cm2), with a typical measurement time of 1 min.

A novel neutron detector for measuring the output of pulsed sources

Abstract A beryllium based detector has been developed which can be used to measure the output of pulsed neutron sources in the D, D and D, T fusion energy regions. The principle of this detector, and its construction, are discussed. The use of the detector in measuring the output from Kaman pulsed neutron sources and from the SPR III reactor at the Sandia National Lab. is discussed. The method used to calibrate the detector is described and theoretical calculations are presented of the variation of its efficiency with energy. The calculations were made using the MCNP and Tiger codes. Some incidental nuclear data measured during the testing of this detector are presented.