Effect of light on the performances of CVD diamond nuclear detectors

CVD (Chemical Vapour Deposited) diamond samples have been characterized by using Am-241 alpha particles in order to look for specific differences of the transport properties between electrons and holes. The effects of "priming" or exposing the samples to large doses of x-rays and to day light and to monochromatic light have been analyzed in some details with respect to charge collection efficiency and to counting efficiency values and their decay as a function of time. It turns out that the effect of priming is slightly larger for holes than for electrons and that only wavelengths in the interval between 350 and 550 nm are effective in changing the collection length. In this interval, hole collection efficiency is decreasing, while for electrons it increases. A possible interpretation of all these effects is presented and discussed, taking also into account luminescence and photoconductivity data.