DOE OSTI2014
As the world supply of helium continues to dwindle, alternatives to neutron detection have been a key focus area of radiation detection research. Solid-state neutron detectors are one possible alternative to the {sup 3}He detectors currently used for neutron detection when large detector areas are not required. Although {sup 6}Li and {sup 10}B are both also commonly used for neutron detection, neither has as high of a thermal cross section as {sup 3}He. The thermal cross sections for {sup 6}Li, {sup 10}B, and {sup 3}He are, respectively, 940 barns, 3840 barns, and 5330 barns. Both boron and helium are used in a gaseous form for neutron detection; however, there is no suitable gaseous form of lithium for neutron detection. Lithium is instead utilized in solid or liquid compounds for neutron detection. In this context, one area of interest is in the development of ternary A{sup I}B{sup III}C{sup IV} semiconductors comprised of isotopically-enriched lithium. Single crystal samples are being prepared through collaboration with the Y12 National Security Complex. This research focuses on the characterization of {sup 6}LiInSe{sub 2} (LISe) crystals, as well as on the development of prototype systems to assess the viability of using LISe crystals as a thermal neutron detector. Data to be obtained will provide previously untested physical parameters to facilitate growth optimization. Eventually, the refined crystals will be developed into solid-state, position-sensitive pixel detectors used for neutron imaging, among a wide array of possible applications including nuclear forensics. For the most part, the research team has been focused on mastering the detector fabrication processes, response tests on the first two batches of crystal samples, and the design of the first iteration detection system (Fig. 2). Response tests using alphas and neutrons have shown sensitivity to both particles. The first iteration detection system developed utilizes a 3-stage filter ladder of resistors and capacitors, similar to an ORTEC 142PC Preamplifier. Ideally, this ladder will reduce the noise associated with the high voltage power supply. The preamplifier is AC coupled to improve its counting rate capability (saturation), and critical components are on insulated posts. The custom circuit is housed in an aluminum box, and initial testing of the circuit has shown expected results. Investigation into further noise reduction is underway and will be the focus of the presented results. Upon completion and successful testing of the final detection system design, further development in spatial resolution and gamma/neutron discrimination will continue. (authors)
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗