Irradiation damage of uridine molecules with MeV heavy ions

In order to study the mechanism of the nucleotide directly damaged by energetic heavy ions, the residual ratio of uridine molecules after irradiation was measured by means of High Performance Liquid Chromatography (HPLC). The experimental results show that the irradiation damage probability depends on the electronic energy loss rate (S_e) of incident ions: first it increases quickly with S_e, then becomes stable when S_e reaches 800 eV/nm. The contribution of the nuclear collisions can be neglected compared with that of the electronic process. This is not only because that the nuclear energy loss rate (S_n) is much smaller than S_e for MeV heavy ions, but also because the energy deposition through the electronic process is more efficient in damaging molecules than through the nuclear process.