Comparison of measured and Monte Carlo simulated track structure parameters in nanometric volumes

The track structure of ionising particles in biological matter can only be assessed by simulations, since neither the type of interaction and its products nor the interaction positions in biological matter can be detected with nanometer resolution. Hence, there is a need to benchmark the deployed computer codes using suitable experimental data. For this purpose, the frequency distributions of ionisation clusters produced in the sensitive volume of the PTB ion counting nanodosemeter by monoenergetic protons and alpha particles (with energies between 0.1 and 20 MeV) were measured. C3H8 and N2 were alternately used as the working gas. The measured data were compared with the results of simulations obtained with the PTB Monte Carlo code PTra. Measured and simulated characteristics of the particle track structure are in good agreement for protons over the entire energy range investigated. For alpha particles with energies above the Bragg peak a good agreement can also be seen, whereas for energies below the Bragg peak differences of as much as 25 % occur.