Experimental Validation of Track Structure Models

A tracking ion counting nanodosimeter was employed to acquire spatial ionization patterns produced by charged particles in propane gas at 1.3 mbar. Data were taken at the James M. Slater MD Proton Treatment and Research Center with 250 MeV, 17 MeV, 5 MeV and 1.5 MeV proton beams, 4.8 MeV alpha particles and electrons from a Sr-90/Y-90 source. For each particle type, measurable quantities used for track structure reconstruction included the number of ionizations and their location within a wall-less, cylindrical sensitive volume measured with a resolution of about 5 tissue-equivalent nanometers, and primary particle coordinates. Measured ionization frequency distributions as a function of distance from particle track were compared with results of a dedicated Monte Carlo track structure code.