Measurement of MeV Ion Track Structure in an Organic Solid.

Abstract

Ion tracks, formed by the interaction of energetic charged particles with matter, have played an important role in the development of modern physics. More recently, MeV-GeV ion track production has been used to modify materials in a controlled manner [1,2], being a potential tool to engineer material properties in the nanometer to micrometer scale. MeV-GeV ions are finding recently wider use in radiation therapy for, e.g., treatment of different forms of cancer. In spite of this, the understanding of the evolution of energy deposited around the path of an ion has not progressed markedly since early works in the sixties and seventies [3‐5]. Ions with velocities higher than the Bohr velocity syB › 0.22 cmynsd deposit their energy in electronic excitation and ionizations in a cylindrically symmetric region around the path of the impacting ion, forming the track core. The incident ions cause ejection of energetic secondary electrons that transport part of this energy out of the core [3,4]. The mean deposited energy density, esrd, after the ion passage is approximated by a esrd ~ r 22 dependence, where r is the radial distance from the ion path. Such a dependence is obtained from