Investigations of high quality diamond detectors for neutron fluency monitoring in a nuclear reactor

We report here on the characterisation of neutron detectors fabricated using a range of synthetic diamonds including polycrystalline as well as single crystal samples. After material characterisations including response to alpha particles (stability, detection efficiency etc), measurements were made using thermalised neutrons in a nuclear reactor at fluencies of 10⁶-10¹⁰ neutrons/cm² s. The readout electronic was based on current preamplification: it enables to locate the electronic preamplifier remotely from the hostile environment, typically at distances that can exceed 20 up to 200 m. It requires high signal to noise ratios for the detection device. To enable the neutron conversion (diamond itself remains transparent to such low energy neutrons) a thin film converting material made of ²³⁵Uranium element is used to emit charged particles that are detected by the diamond film. The device responses were studied in terms of sensitivity, response time, reliability, and conformity with respect to the fluency as measured using calibration fission chambers. The results exhibit remarkable linearity and stability. The fabricated devices display are capable of faithfully following the power cycles of a nuclear reactor. With respect to gas ionisation chambers, these devices of much smaller dimension can find a use for neutron fluency profiling with high position resolution.