Hand-held Neutron Detectors

Proliferation of the weapons of mass destruction such as nuclear weapons is a serious threat and prevention of their spread has reached a state of heightened urgency in recent years. One of the ways to passively determine the presence of nuclear weapons is to detect and identify characteristic signatures of highly enriched uranium and weapons grade plutonium. Neutrons and gamma rays are two signatures of these materials. Gamma ray detection techniques are useful because the presence of gamma rays of specific energies can confirm the presence of a particular isotope. This technique however, has one significant limitation. In the presence of a dense surrounding material such as lead, gamma ray attenuation can be significant. This can mask the gamma signatures of these special nuclear materials (SNM). Neutrons, on the other hand, easily penetrate dense and high atomic number materials. For heterogeneous or dense materials such as samples of metals, oxides, and nuclear waste, gamma ray attenuation is too high to permit accurate correction of the measured signal. Under these circumstances, passive assay techniques based on neutron detection are preferable. When detected, neutrons directly indicate the presence of spontaneously fissioning isotopes (plutonium and californium) and induced fissions (uranium). Therefore, neutron detection is an important component of the overall detection techniques used in identifying SNM. In radioisotope identification devices to date, the neutron detection was readily achieved using He-3 tubes. Unfortunately, in recent years the quantities of this gas are becoming limited, therefore, new solutions are required for an efficient detection system that would allow neutron detection with an ability to discriminate gamma events from neutron events. Gamma discrimination is critical because gamma rays are common background in neutron detection environment during SNM monitoring. In this project we propose a hand-held thermal neutron detector based on an elpasolite scintillator. Anticipated Benefits The goal of this project is to create a hand-held thermal neutron detector that can replace He-3 devices with similar or better performance. Detectors developed in the frame of this project will mainly find their application in nuclear monitoring areas, such as nuclear treaty verification, safeguards, environmental monitoring, nuclear waste cleanup, and border security. Other fields will also benefit from the advancement of the CLYC detection systems. Routinely, neutrons are employed to investigate structures of biological molecules or crystals. Nuclear and particle physics are other fields of science were thermal neutron detectors are used (e.g. n-n scattering experiments, fission of heavy nuclei). CLYC neutron sensors could also be used in other areas. With the increased interest and commitment to quality control, many industrial groups are developing neutron based non-destructive testing equipment. References Dr. Stephen Payne, LLNL, 7000 East Avenue, Livermore, CA 94550, 925-423-0570, payne3@llnl.gov Dr. Zhong He, U. of Michigan, 2355 Bonisteel Boulevard, Ann Arbor, MI 48109, 734-764- 7130, hezhong@umich.edu Dr. William Moses, LBNL, 1 Cyclotron Road, Berkeley, CA 94720, 510-486-4432, WWMoses@lbl.gov