Lithium and boron based semiconductors for thermal neutron counting

Abstract

ABSTRACT Thermal neutron detectors in planar configuration were fabricated from LiInSe 2 and B 2 Se 3 crystals grown at RMD Inc. All fabricated semiconductor devices were characterized for the current-voltage (I-V) characteristic and neutron counting measurement. Pulse height spectra were collected from 241 AmBe (neutron source on all samples), as well as 137 Cs and 60 Co gamma ray sources. In this study, the resistivity of a ll crystals is reported and the collected pulse height spectra are presented for fabricated devices. Note that, the 241 AmBe neutron source was custom designed with polyethylene around the source as the neutron moderator, mainly to thermalize the fast neutrons before reaching the detectors. Both LiInSe 2 and B 2 Se 3 devices showed response to thermal neutrons of the 241 AmBe source. Keywords: Thermal neutron counting, LiInSe 2 , B 2 Se 3 , semiconductor detector 1. INTRODUCTION Proliferation of weapons of mass destruction, such as nuclear weapons, is a serious threat in the world today. Preventing the spread of nuclear weapons has reached a state of heighten ed urgency in recent years. On e way 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 the drawback of gamma-ray attenuation in the presence of dense surrounding material such as lead. This can mask the gamma-ray signature s of these special nuclear materials (SNM). Neutrons, on the other hand, easily penetrate dense, high atomic number materials, compared to gamma rays and are a direct indicator of the presence of isotopes that undergo spontaneous fission (plutonium and californium) or induced fission (uranium). Thus, neutron and gamma-ray detection are complementary a nd vital components of the overall detection scenario used in identifying SNM. At present, there is a real need for compact detection systems that would be capable of efficient neutron and gamma-ray detection. To develop new semiconductor radiation detectors for identification of special nuclear materials, LiInSe