Neutron detection with cryogenics and semiconductors

Abstract

PACS 29.30.Hs, 29.40.Vj, 29.40.Wk The common methods of neutron detection are reviewed with special attention paid to the application of cryogenics and semiconductors to the problem. The authors' work with LiF-and boron-based cryogenic instruments is described as well as the use of CdTe and HgI 2 for direct detection of neutrons. 1 Introduction Advances in materials and methods have enabled the detection of radiation by means today that would have seemed, to pioneers in the field a century ago, like science fiction. Improvements in technology have resulted, for gamma ray detection, in high-purity germanium operating at 77 K and providing 0.1% energy resolution above 1 MeV, more than an order of magnitude improvement over what was (and still is) achievable by scintillators. However, operating below 1 K, cryogenic calorimeters have been used in X-ray astronomy, in the search for dark matter, and more recently in gamma ray spectroscopy, and have achieved better than 70 eV resolution at 60 keV [1], a factor of 4 to 5 improvement over what can be achieved by germanium at that energy. Meanwhile, at the other end of the temperature spectrum, the development of new, wide band-gap semiconductors has sparked research in room temperature gamma ray detectors and has held out the hope of 1 -2% resolution and freedom from cryogenics [2,3].With such results being reported from the X-and gamma ray world it is natural to examine the possibilities for neutron detection. A cryogenic neutron detector would operate by detecting the heat pulses caused by neutron capture and scattering, while a semiconducting detector would detect the nuclear reaction products from a sensitizer (for example, fission fragments detected in a 235 U-coated Si diode) or from some constituent of the semiconductor.In the following sections, the common methods of neutron detection are described and their deficiencies with respect to neutron spectroscopy at energies above thermal (0.025 eV) are outlined. Published work on neutron-detecting cryogenic calorimeters will be reviewed and work by the present authors on boron-and lithium-based instruments will be discussed. Turning to semiconductors, we review work with coated and native (uncoated) semiconductor, including Cd 1-x Zn x Te (CZT) and HgI 2 , as applied to neutron detection. Results obtained by the authors with HgI 2 will be shown.

The all boron carbide diode neutron detector: Comparison with theory

“…The de-excitation of 114 Cd contains many gamma rays emitted in cascades [9], which do not appear to be detected in our device-consistent with an absence of pulses caused by a radioactive 60 Co gamma emitter source. In effect, these all boron carbide devices appear to largely gamma blind.…”

“…Boron carbide thin fi lm diodes and devices have begun to attract attention as potentially highly effi cient solid state neutron detectors [8][9][10]. This interest has been spurred on because 10 B has a high cross-section (approximately 3800 barns) for neutrons at lower energies (~25 meV), based on the 10 B(n, α) 7 Li neutron capture reactions: 10 …”

“…Perhaps because of confusion between dielectric and semiconducting polytypes of boron carbide and boron carbides with only modest sheet resistance, there has been considerable controversy as to whether an all boron carbide semiconducting diode can act as a neutron detector [7,9,11,12]. This controversy has been somewhat addressed by the fabrication of all boron carbide neutron detectors [4,6] from semiconducting polytypes of boron carbide.…”

The coadsorption and interaction of molecular icosahedra with mercury

“…Neu tron detectors with boron carbide have begun to attract attention [7][8][9]. Boron has high cross section for neutrons at lower energies, with capture processes: n + 10 B → 7 Li + 4 He + γ n + 10 B → 7 Li + 4 He n + 10 B → 11 B + γ Several isotopes of mercury (Hg)have a high neutron cross section at higher neutron energies [10].…”

A Handheld Neutron-Detection Sensor System Utilizing a New Class of Boron Carbide Diode

“…with 94% and 6% probabilities, respectively [5], [6]. Thus, an incoming epithermal (very low energy) neutron strikes a 10 B atom, producing 7 Li and 4 He capture products, which can generate a substantial amount of electron-hole pairs due to their significant kinetic energies (generally 0.84 MeV for Li and 1.47 MeV for He).…”