Year
2004
Abstract
A shuffler is a nondestructive assay diagnostic instrument that induces fissions in a sample and then measures the resulting delayed neutrons. From the delayed neutron count rate the fissile material mass in that sample is determined. The name shuffler comes from the fact that a Californium-252 source is rapidly moved (shuffled) between the assay chamber and a shielded chamber. The delayed neutrons are measured while the Californium is shielded. The purpose of this paper is to report on the ramifications of switching the neutron source in a shuffler from a Californium isotopic source to a deuterium - tritium based neutron generator. This difference will be examined in the context of assaying HEU inside of a highly moderating container. This work involves a major modification of a classic neutron diagnostic method-the shuffler; in fact, implementing this change would require changing the name for the method. The shift involves changing from an energy spectrum with an average energy of 2-MeV to a mono-energetic source at 14-MeV. We will address the following questions: What will the shift in energy do particularly in the context of fissioning 238U? How will the total neutron flux emitted by the generator be quantified? Is penetration of the interrogating flux into the uranium significantly enhanced by the change in energy?