Year
2008
Abstract
In previous years, advancements have been made in portable neutron coincidence counters. These detectors have the ability to quickly detect possible special nuclear materials in the field. However, the uncertainties with the measurements can quickly increase as the number of neutrons being counted simultaneously increases due to accidental neutrons being recorded. During a spontaneous fission event in a sample, coincident neutrons and coincident gamma-rays are emitted. In theory, these signals could be used together without resulting in increasing the order of the error in the result. In this task, the design of a portable coupled neutron and photon coincidence counter will be explored. With the use of MCNPX and MCNP-POLIMI, a counter can be modeled to simulate a source and count both neutrons and gammas. The detector will use multiple Helium-3 (3He) tubes embedded in high density polyethylene to detect coincidence neutrons. It will also use multiple Lanthanum Bromide (LaBr) scintillation detectors to detect coincident gamma rays. The LaBr detector will also provide the ability to perform spectroscopy to assist in determining the isotopes present in the source. A coincident event will occur from a neutron-neutron, gamma-gamma, neutron-gamma, and gamma-neutron being detected in coincidence within a specified amount of time. These detectors can be arranged to surround the source and to provide the best geometry for the best efficiency. With these two types of detectors working in conjunction, it will provide a new method to determine possible special nuclear materials quickly and with less error in the field.