Track structure of heavy ions and high-LET effects

Abstract

  We measured the energy and angular distributions (7-10000 eV and 20°-160°) of secondary electrons produced in the collision of 6.0 MeV/u He²⁺ ions with water vapor, in order to discuss a relation between the track structure and high-LET effects. From these measurements the doubly differential cross sections (DDCS) of electron emissions were deduced with an estimated uncertainty of ±13%. The energy distribution (SDCS) was also obtained by integrating the DDCS values with respect to the ejected angles, and compared with the empirical model of Rudd. The energy spectrum (SDCS) showed a good agreement with the model of Rudd in the energy range <100 eV. However, in the range 100-1000 eV the SDCS showed large discrepancies by -40%, and was nearly twice greater in the region >3keV. To assess the new cross sections these values were incorporated in the kurbuc Monte Carlo track structure code system for simulation of secondary electrons. Radial dose distributions were obtained by analyzing the tracks generated by the code kurbuc using the new DDCS values. In the core with the radius (r) less than 1 nm the dose is very high due mainly to excitation events induced by low-energy electrons, while the penumbra shows a well-known r^-2 dependence.