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 et al., 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 ${}^6\text{L}\text{iF}$ converting layer. Fast neutrons are directly detected in the CVD diamond bulk, since they have enough energy to produce the ${}^{12}\text{C}\left(n,\alpha \right){}^9\text{B}\text{e}$ reaction in diamond. Thermal neutrons are instead converted into charged particles in the ${}^6\text{L}\text{iF}$ layer through the ${}^6\text{L}\text{i}\left(n,\alpha \right)T$ nuclear reaction. These charged particles are then detected in the diamond layer. The thickness of the ${}^6\text{L}\text{iF}$ 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 ${}^6\text{L}\text{i}\left(n,\alpha \right)T$ and the ${}^{12}\text{C}\left(n,\alpha \right){}^9\text{B}\text{e}$ 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 ${}^6\text{L}\text{iF}$ 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.