Diamond Neutron Detectors as He-3 alternative

In this paper we present recent results regarding the use of synthetic CVD Diamond as an alternative to He-3 for Neutron Detectors fabrication. Diamond radiation detectors are able to detect deep UV photons, X-rays, gamma rays, electrons, alpha particles, charged ions and neutrons, with a dynamic range in energies spanning from 5.5 eV up to GeV of cosmic rays. Since the bandgap of diamond is 5.5 eV this leads into a negligible dark current noise at room temperature with no need or cooling. Unlike He-3 gas filled tubes, diamond radiation detectors are generally designed as a parallelepiped solid-state ionization chamber. A charged particle, or a photon with energy above the bandgap, passes through the diamond and ionizes it (energy to form e-h pair: 13 eV) generating electron-hole pairs, which are separated by the electric field between the electrodes. Fast neutrons are detected directly in the bulk of the intrinsic diamond layer through the C-12 (n,α) Be-9 and C-12 (n,n´) C-12* reactions [1]. The produced Be-9 and α ions have a total energy: Eα + Be = En 5.7 MeV where En is the energy of the impinging neutron. To detect both fast and thermal neutrons a layer of Li-6F or B-10 allows the conversion of low energy neutrons into highly ionizing particles. Diamond has the highest atomic density of any material, this translates into a high neutron efficiency per unit volume, and in particular it appears to have the highest intrinsic efficiency for fission neutron detection per unit thickness with experimental efficiency values at 2.5 and 14 MeV of 2.2 and 2.4%/mm respectively [2]. Apart from neutron counting, novel diamond neutron detection systems developments show excellent results for fast neutron spectroscopy (FWHM of 56 keV for 5-20.5 MeV neutrons) [3], time-of-flight measurements, as well as for neutron imaging, making diamond a interesting alternative to He-3 based neutron detectors.