Single-crystal diamonds for neutrons

Abstract

Single-crystal Chemical Vapour Deposition (CVD) diamond detectors feature a superb Signal-to-Noise ratio (S/N , timing response and good energy resolution. These properties make CVD diamonds interesting for neutron detection. In the present contribution we discuss different measurements of neutron energy with CVD diamonds applied to relatively low- and high-energy neutrons. For the low-energy range a compact neutron Time-of-Flight (ToF) spectrometer for high flux environments has been developed. Such a detector would allow the measurement of neutron spectra in the range from 250keV up to few MeV with 20–40% resolution in the neutron fluxes 105 < φn < 109 n/cm2/s. The first prototype of this spectrometer was tested at ENEA FNG 3MeV quasi-monochromatic neutron beam and demonstrated feasibility of the concept. However, the test evidenced inadequacy of existing amplifiers providing insufficient timing resolution to extract a sensible neutron spectrum in MeV range. This particular diamond detector application, among with many others, calls for a development of a fast amplifier featuring an order of magnitude higher Signal-to-Noise ratio. On the other hand, to measure the neutron flux in a wide neutron energy range (1–100 MeV) at counting rate ∼ 2 MHz a single diamond crystal coupled to a fast (tens of ns) shaping preamplifier was used. The test performed at the n_TOF neutron beam line at CERN revealed the capability of using such a detector for spectroscopic measurement: the energy resolution achieved is about 4% at the n-α peak at 9.3 MeV, i.e. for 15 MeV neutrons. CVD diamond detectors have been proposed, successfully tested and applied as neutron flux monitors in nuclear reactor and around tokamaks. Furthermore, the possibility to extend the application of diamond films to neutron spectroscopy for a wide range of applications can be envisaged and already tested in fusion tokamak and around accelerators.