Fabrication reproducibility and high performance reliability were obtained in fissile-material-free thermal neutron detectors based on chemical vapor deposited diamond in a multilayered p-type/intrinsic/metal design. Under α particle irradiation, all the detectors (more than ten) have shown 100% charge collection efficiency and approximately 1.5% energy resolution. A Li6F layer was deposited on the detector surface as converting material for thermal neutrons through the Li6(n,α)T nuclear reaction. Both the 2.73MeV tritium and the 2.06MeV α peaks are detected and clearly resolved. Stable performance and excellent linear behavior of the count rate versus the incident neutron flux were observed.

Thermal neutron flux monitors were fabricated using chemical vapor deposited single crystal diamond in a p-type/intrinsic/metal/⁶LiF layered structure. They were placed 80 cm above the core midplane of a 1 MW research fission reactor, where the maximum neutron flux is 2.2×10⁹ neutrons/cm² s. Good stability and reproducibility of the device response were observed over the whole reactor power range. A 150 000 counts/s count rate was measured at the maximum reactor power with no degradation of the detector signal. As the multiple pile-up process due to the slow readout electronics is accounted for, an excellent linearity of the diamond response is observe

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 ⁶LiF converting layer. Fast neutrons are directly detected in the CVD diamond bulk, since they have enough energy to produce the ¹²C(n, α)⁹Be reaction in diamond. Thermal neutrons are instead converted into charged particles in the ⁶LiF layer through the ⁶Li(n, α)T nuclear reaction. These charged particles are then detected in the diamond layer. The thickness of the ⁶LiF 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 ⁶Li(n, α)T and the ¹²C(n, α)⁹Be 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 ⁶LiF 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

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