Design and Performance Evaluation of a Diamond Detector for Thermal and Fast Neutrons

摘要: Diamond, especially electronic-grade CVD diamond, was considerated as promising material for neutron detection used in harsh environment with high temperature and high-intensity radiation field, due to the wide bandgap, high carrier mobility, fast response and excellent radiation resistance. In this study, a new diamond-based neutron detector could be used for both thermal and fast nuetrons was designed and fabricated, and good performance was found after tested. Using Monte Carlo simulation,the structure of the detector, the thickness of neutron-sensitive material, and therotical response to neutrons of the overall system were analyzed in detail. After careful optomization, enriched ⁶LiF(up to 95%) was chosen as neutron sensitive materail and the thickness of the conversion layer was optimized as 17-μm for thermal neutron detection , and the therotical intrinsic thermal neutron efficience was calculated as about 5.47%. The response of the detector to fast neutrons via (n, ¹²C) reaction was also simulated and validated with neutron energy of 14.1 MeV. Based on the optimized detector design, electronic-grade CVD diamond produced by Element Six company with dimensions of 4.5 mm × 4.5 mm × 0.5 mm was used to develope neutron detectors. Ti/Au electrodes (35 nm/120 nm) were deposited on the device through magnetron sputtering and the 6LiF powder was compressed to dense pieces by cold-pressing process. A copper housing with PCB-based packaging and bonding was also designed to install the diamond detector. The charge particle performance was characterized by alpha particles from ²⁴¹Am source, yielded an efficiency of charge collection of 99.5% and an energy resolution of 1.87%. Thermal neutron detection efficiency was measured in a ²⁵²Cf thermal neutron field, yielding efficiencies of 1.199% and 1.097% at different discrimination thresholds. These values are in good agreement with the simulated efficiency of 1.17%. The fast neutron response was measued by a D-T neutron generator with mono energy of 14.1 MeVand the resualts also agreed well with the Gaussian-broadened simulated spectrum. These results demonstrate the feasibility of the fabricated detector for both thermal measurements and the detection of fast neutrons.