Upgrade of compact neutron spectrometer for high flux environments

Abstract: In this paper a new version of Li6-based neutron spectrometer for high flux environments is described. The new spectrometer was built with commercial single crystal Chemical Vapour Deposition diamonds of electronic grade. These crystals feature better charge collection as well as higher radiation hardness. Ohmic metal contacts were deposited on the diamonds suppressing build-up of space charge observed in the previous prototypes. New passive preamplification of signal at detector side was implemented to improve the resolution. This preamplification is based on RF transformer not sensitive to high neutron flux. Compact mechanical design allowed to reduce detector size to a tube of 1 cm diameter and 13 cm long. The spectrometer was tested in thermal column of TRIGA reactor and at DD neutron generator. The test results indicate an energy resolution of 72 keV (RMS) and coincidence timing resolution of 68 ps (RMS). The measured data are in agreement with Geant4 simulations except for larger energy loss tail presumably related to imperfections of metal contacts and glue expansion.