Application of the liquid drop model to heavy ion irradiations

The diameters of the tracks obtained theoretically for low energy ions in organic materials, as predicted by the models based on the deposited dose by secondary electrons, are remarkably lower than those experimentally obtained by replica methods at submicroscopic levels. This discrepancy between experimental and theoretical data was then attributed to thermal explosion phenomena. In the present work the 'Liquid Drop Model' was extended to insulators in order to assess the problem from a different point of view. The deposited energy on the lattice and on the electrons for a given ion, were initially considered, then the thermal peak evolution was studied. The material investigated was a polycarbonate used in radiobiology, known commercially a Makrofol-E or Lexan, and the specifically studied energies were located in the 1.4 to 100 keV/amu range. A critical temperature of 350 K was adopted, above which an appreciable damage is introduced in the material. After the thermal evolution, the track radius is deduced for the considered ion. The model allows the formation of tracks for ions in an energy range considered forbidden in the literature. The application of the proposed model, shows that there still exist discrepancies between the values predicted theoretically and those experimentally obtained, which suggests the need for further adjustments of the model. (author)