Absorption parameters of deuterium ions in molybdenum

Abstract

The capture parameters of deuterium ions in molybdenum have been studied in this paper. It has been shown that the capture coefficients decrease as the dose and the irradiation temperature increase and they increase as the energy and flux density of the ions increases. Upon heating after irradiation or exposure in a vacuum even at room temperature the number of deuterons captured in molybdenum decreases. At a raised temperature the capture coefficients measured from the gas generation spectra with heating after irradiation turn out to be smaller than the coefficients measured from the gas generation right during the irradiation. It has been established in measurements of the spectra of deuterium gas generation that the accumulation of deuterium in molybdenum occurs with a different binding energy of the deuterons in the metal. As the deuterium accumulates in the sample, those sites at which the deuterium is most strongly bound are gradually filled up and saturated. At large doses most of the deuterium is poorly retained in the metal and can be liberated into a vacuum either in the course of irradiation or during the subsequent heating. First of all, the deuterium is liberated most rapidly from the weakly bound states. It has been shown that in addition to thermal gas generation processes there is gas generation stimulated by the ion beam retarded in the sample. The contribution of radiatively stimulated gas generation at a low temperature and a high irradiation dose is especially important. A comparative analysis has been made of the results obtained by different authors, and the possible causes for the discrepancy between the experiments have been explained. It has been shown that the various results can be produced both by a difference in the irradiation parameters (which are sometimes assumed without justification to be unimportant and are not even indicated in the papers) and by a difference in measurement procedures.