Track structure of carbon ions: measurements and simulations

The likelihood of radiation to produce clustered damages in irradiated biological tissue and the reparability of such damages are closely related to the stochastics of localised ionising interactions within small volumes of nanometre sizes, determined by the particle track structure. Track structure investigations in nanometre-sized volumes have been subject of research for several decades, mainly by means of Monte Carlo simulations. Today, the 'track-nano-dosimeter', installed at the TANDEM-ALPI accelerator complex of LNL, is a measuring device able to count the electrons produced in a 20-nm equivalent sensitive site (De Nardo et al. A detector for track-nanodosimetry. Nucl. Instrum. Methods. Phys. Res. A 484, 312-326 (2002)). It allows studying track structure properties both in the near neighbourhood of a primary particle trajectory and separately in the penumbra region. An extended study for different ionising particles of medical interest has been recently performed with the track-nano-dosimeter (Conte et al. Track structure of light ions: experiments and simulations. New J. Phys. 14, 093010, (2012)). Here, new experimental data and results of Monte Carlo simulations for 240- and 96-MeV 12C-ions are presented and discussed. In conclusion, it can be stated that the shape of the ionisation cluster-size distributions in the track-core region of particles' tracks results to be mainly determined by the mean free ionisation-path length of the primary particles. In the penumbra region, the shape of the distributions is almost independent of the impact parameter and also of the particle type and velocity. The probability of target hits changes with the quality of the primary particles, but the hit target experiences the same ionisation clustering, irrespectively of particle type and velocity. The relative frequency of target hits results to be proportional to the mean number of ionizations produced by the primary particle along a path length D. (authors)