Characterization of silicon carbide and diamond detectors for neutron applications

Abstract

The presence of carbon atoms in silicon carbide and diamond makes these materials ideal candidates for direct fast neutron detectors. Furthermore the low atomic number, strong covalent bonds, high displacement energies, wide bandgap and low intrinsic carrier concentrations make these semiconductor detectors potentially suitable for applications where rugged, high-temperature, low-gamma-sensitivity detectors are required, such as active interrogation, electronic personal neutron dosimetry and harsh environment detectors.A thorough direct performance comparison of the detection capabilities of semi-insulating silicon carbide (SiC–SI), single crystal diamond (D–SC), polycrystalline diamond (D–PC) and a self-biased epitaxial silicon carbide (SiC–EP) detector has been conducted and benchmarked against a commercial silicon PIN (Si–PIN) diode, in a wide range of alpha (Am-241), beta (Sr/Y-90), ionizing photon (65 keV to 1332 keV) and neutron radiation fields (including 1.2 MeV to 16.5 MeV mono-energetic neutrons, as well as neutrons from AmBe and Cf-252 sources).All detectors were shown to be able to directly detect and distinguish both the different radiation types and energies by using a simple energy threshold discrimination method. The SiC devices demonstrated the best neutron energy discrimination ratio (( MeV)/( MeV) ≈5), whereas a superior neutron/photon cross-sensitivity ratio was observed in the D–PC detector ((AmBe)/(Co-60) ≈16). Further work also demonstrated that the cross-sensitivity ratios can be improved through use of a simple proton-recoil conversion layer.Stability issues were also observed in the D–SC, D–PC and SiC–SI detectors while under irradiation, namely a change of energy peak position and/or count rate with time (often referred to as the polarization effect). This phenomenon within the detectors was non-debilitating over the time period tested (5 h) and, as such, stable operation was possible.Furthermore, the D–SC, self-biased SiC–EP and semi-insulating SiC detectors were shown to operate over the temperature range °C to °C.