Spectra of secondary electrons generated in water by energetic ions

TL;DR

This paper presents a new parameterization method for calculating secondary electron spectra generated by energetic ions in water, relevant for hadron therapy, enabling fast and accurate depth-dependent energy distribution predictions.

Contribution

Introduces a novel parameterization of ionization cross sections for low-energy ions and compares dielectric response models for high-energy ions in water.

Findings

New parameterization accurately predicts secondary electron spectra near the Bragg peak.

Method allows rapid calculation of energy spectra at various depths.

Comparison of models enhances understanding of ion-water interactions.

Abstract

The energy distributions of secondary electrons produced by energetic carbon ions (in the energy range used, e.g., in hadron therapy), incident on liquid water, are discussed. For low-energy ions, a new parameterization of the singly-differential ionization cross sections is introduced, based on tuning the position of the Bragg peak. The resulting parameterization allows a fast calculation of the energy spectra of secondary electrons at different depths along the ion's trajectory, especially near the Bragg peak. At the same time, this parameterization provides penetration depths for a broad range of initial-ion energies within the therapeutically-accepted error. For high-energy ions, the energy distribution is obtained with a use of the dielectric response function approach. Different models are compared and discussed.