Results of Alpha Irradiation of Diamond Sensors

In a neutron generator, deuterium ions are accelerated towards a tritium-loaded target. From the nuclear reaction that may result from their interaction, an alpha particle and a neutron are emitted back-to-back. The neutron escaping the chamber can be used for tomography of a high-Z material, while its trajectory can be better calculated if the trajectory of the relative alpha, much easier to detect, is known. This technique is called Associated Particle Imaging (API). Existing API systems, available commercially, have several limitations. A semiconductor-based API detector placed inside the vacuum chamber is believed to outperform all previous families of API detectors. In the past years, we have shown how silicon can withstand the alpha fluence expected during the neutron generator lifetime. As such, it will be the semiconductor material of choice for our API detector. However, looking forward to an upgrade, we want to evaluate the radiation hardness against alphas of diamond sensors, which is another kind of detector that is routinely fabricated at Brookhaven National Laboratory (BNL). We exposed a single channel diamond sensor, mounted on the same set-up used for the irradiation tests on silicon diodes, to the same radioactive source used during the silicon irradiation: a 5 MeV alpha flux generated by an 241Am radioactive source. During irradiation, the diode was kept biased and waveforms were acquired from time to time at positive and negative voltages, while data analysis was performed off-line.