Spatial patterns of ioniziation in charged-particle tracks

The physical structure of charged-particle tracks plays an important role in determining the response of a stopping material to the absorption of energy following irradiation by charged particles and neutrons. For biological systems, and for microelectronic circuits, the response is sensitive to the energy deposited in submicron-size volume elements. Because of the stochastic nature of energy deposition in and near charged particle tracks, there may be wide variations in the actual quantities of energy deposited in critical volume elements. Since direct measurements of energy deposition in condensed material (solids or liquids) are technologically infeasible, the effects of charged-particle track structure are usually estimated from one of several model calculations; the most commonly used are homogeneous track structure models. Recent interest in the radiation biology of high Linear-Energy-Transfer (LET) radiation has spurred interest in testing these model descriptions of the structure of high-energy heavy-ion tracks. As one means of providing such tests, experiments were recently conducted at the GSI-Darmstadt, UNILAC accelerator, to measure energy deposition in small volumes as a function of the radial distance from the path of fast, heavy ions. These measurements, conducted in collaboration with research groups of Dr. G. Kraft at GSI and Prof. Schmidt-Boecking of the University of Frankfurt, were made for simulated tissue volumes 0.5 and 1.0 μm in diameter, located from 0--10 μm from the path of Ge ions having energies from 13.0--17.2-MeV/amu. Excellent agreement was observed between model calculations and measured dose distributions for radial distances up to a few micrometers in simulated tissue. 6 refs., 4 figs