Abstract
The presence of carbon atoms in silicon carbide and diamond makes the materials ideal candidates for direct fast neutron detectors. Furthermore the low atomic number, strong covalent bonds, high displacement energies, wide band gap 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 semiinsulating 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), ionising photon (65keV to 1332keV) and neutron radiation fields (including 1.2MeV to 16.5MeV 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 (Emax[n=5MeV] / Emax[n=1MeV] ~5), whereas a superior neutron/photon cross sensitivity ratio was observed in the D-PC detector (Emax[AmBe] / Emax[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, that being a change of energy peak position and/or count rate with time (often referred to as polarisation effect). This phenomenon within the detectors was non-debilitating over the time period tested (>5h) and as such, stable operation was possible. Furthermore, the D-SC, self-biased SiC-EP and a semi-insulating SiC detector were shown to operate over the temperature range -60C to +100C.