Long-term variation in nuclide activities under laser ablation of metallic targets in aqueous solutions of uranium salt

The long-term variation in the activities of nuclides belonging to the uranium series after laser irradiation of metallic targets (Au, Be, Al, Ti) in aqueous solutions of UO₂Cl₂ has been experimentally investigated. It is found that the activity of ²³⁴Th, in contrast to unirradiated solution, continues to increase for 50 to 60 days after laser irradiation and, having reached a stationary level, remains at it for a long time (about 1 yr). The activity dynamics is modeled theoretically on the assumption that a fraction of ²³⁸U in the irradiated solution is under peculiar conditions, so that its half-life ismuch shorter than that of spontaneous α decay of this nuclide under normal conditions. Possible mechanisms of variation in the shape of the potential barrier for α-particles in the presence of nanoparticles formed by laser ablation of targets are discussed.