Observations of the latent track structure in polymers by diffusion measurements

Abstract

The diffusion constants of ion irradiated Makrofol KG polycarbonate (PC) sheets have been measured with argon and nitrogen as diffusion gas. In order to determine the characteristics of the original latent tracks the material was not etched. The polymers were irradiated with uranium, gold, lead and selen ions at energies of about 10 MeV/u and different fluences in the range of 10 11 ions/cm 2. We used stacks with layers of 8 μm thickness for the irradiation. This allowed us to relate a definite energy loss to each layer and to examine the dependence of the diffusion constant on the energy loss. Additionally we irradiated polymers with 180 keV electrons. The irradiation there was performed with constant energy and current. As reference the diffusion constant of pristine material (i.e. the untreated material) was also measured. Thus the results found with Makrofol KG were checked under different conditions. The ion irradiated probes show two quite different dependencies of the diffusion constant on the ion energy loss. These effects are strongly related to the fluence and the flux of the irradiation. In case of low fluences the diffusion constant is up to 8 times higher than that of the pristine material. In the probes irradiated with high fluences we observed a decrease of the diffusion constant down to half the value of the pristine material. All probes irradiated with high fluences have visibly changed to a brittle material. The electron irradiated probes only show the decrease of the diffusion constant. The material has also visibly changed. To understand the dependence of the diffusion constant on the energy loss we suggest a model. As a result of this model we achieve an average radius of the latent track. Its values show a strong dependence on the ion energy loss. The calculated values vary from 9 to 25 nm.