DECONTAMINATION OF METAL SURFACES ARTIFICIALLY CONTAMINATED WITH Cs~+ IONS BY A LASER ABLATION

摘要

A Q-switched Nd:YAG laser with a 1064 nm and 450 mJ/pulse was employed to study the decontamination characteristics of Type 304 stainless steel specimens artificially contaminated with Cs~+ ions. The specimens were treated with KCl and KNO_3, respectively. The optimum number of laser shots for the system was determined at a given fluence of 57.3 J/cm2. The relative atomic molar ratio of a metal surface was determined by EPMA. For all the test specimens, more than 95% of the Cs~+ ions were removed by the application of 42 laser shots. Cs~+ ion removal efficiency could be improved by the addition of nitrate ions to the contaminated metal surface. A specimen treated with a KCl solution was more difficult to decontaminate in the experimental range. Before and after the laser irradiation, the morphology of the metal surfaces was investigated by SEM and XPS. Dusts generated during the laser irradiation were found to accumulate around a crater of the specimen treated with the KCl solution. By analyzing the XPS spectra of the KCl system, it was found that the ablated Cs~+ ions formed an oxide in air. The higher decontamination efficiency of the KNO_3 system could be attributed to the decomposition of the nitrate ions at a relatively low temperature and the easy reaction of the Cs~+ ions with the oxygen generated from the decomposition of nitrate ions.