Year
2003
Abstract
A new neutron multiplicity counter is being developed which utilizes the fast response of liquid scintillator (NE-213) detectors. Current coincidence counting methods rely on material samples conforming to standards of uniformity, geometry, material type, etc. There exists a wide range of material throughout the DOE complex where these attributes are non-standard or unknown. A fast neutron counter with short die-away time makes possible a higher order multiplicity counting method which can more accurately assay many of the problem items in the inventory. In addition, such a counter would allow for rapid inventory measurements of all forms of uranium. Liquid scintillator detectors also allow for discrimination between interrogation source neutrons and fission neutrons, allowing for even greater assay sensitivity. The detector is sensitive to gamma radiation, but the difference in the charge pulse timing of gamma-ray and neutron events allows for discrimination using pulse shape analysis (PSA). Compact front-end electronics were designed and fabricated to carry out the PSA to separate the neutron events from the gamma-ray events. To accommodate the fast timing, a commercially available time interval analyzer (Guidetech GT657) was employed in place of a more conventional shift register. The front-end electronics was tuned to minimize the amount of gamma leakage into the neutron signal. The separation of gamma and neutron signals as a function of energy was measured using AmLi and 252Cf source data. The results of these studies are presented. This work is supported by the Office of Safeguards and Security.