Thermal and fast neutron detection in chemical vapor deposition single-crystal diamond detectors

Recently, a compact solid-state neutron detector capable of simultaneously detecting thermal and fast neutrons was proposed [M. Marinelli , Appl. Phys. Lett. 89, 143509 (2006)]. Its design is based on a p-type/intrinsic/metal layered structure obtained by Microwave Plasma Chemical Vapor Deposition (CVD) of homoepitaxial diamond followed by thermal evaporation of an Al contact and a (LiF)-Li-6 converting layer. Fast neutrons are directly detected in the CVD diamond bulk, since they have enough energy to produce the C-12(n,alpha)Be-9 reaction in diamond. Thermal neutrons are instead converted into charged particles in the (LiF)-Li-6 layer through the Li-6(n,alpha)T nuclear reaction. These charged particles are then detected in the diamond layer. The thickness of the (LiF)-Li-6 converting layer and the CVD diamond sensing layer affect the counting efficiency and energy resolution of the detector both for low- (thermal) and high-energy neutrons. An analysis is carried out on the dynamics of the Li-6(n,alpha)T and the C-12(n,alpha)Be-9 reactions products, and the distribution of the energy released inside the sensitive layer is calculated. The detector counting efficiency and energy resolution were accordingly derived as a function of the thickness of the (LiF)-Li-6 and CVD diamond layers, both for thermal and fast neutrons, thus allowing us to choose the optimum detector design for any particular application. Comparison with experimental results is also reported. (C) 2008 American Institute of Physics.