Single charge exchange in collisions of energetic nuclei with biomolecules of interest to ion therapy

Abstract

This study is on the theory of single electron capture by fast nuclei from a variety of molecular targets of biological significance with high relevance to ion therapy of deep-seated tumors. The adopted theoretical framework is that of the first principles of quantum physics. As such, no free, adjustable parameters are used. This is in sharp contrast to the associated existing cross section input data to Monte Carlo simulations that all abound with empirical/phenomenological formulae. The present theory has the well-established track of its predictive power. This means that the computed cross sections can confidently be used in the cases for which no experimental data exist. These cross sections are from the full continuum distorted wave method (CDW). We first compute atomic cross sections in the independent electron model and then generate the corresponding molecular cross sections. The latter follow from the former within the independent atom model accompanied by the Bragg additivity rule. The investigated atomic targets are from the backbone of DNA and/or RNA molecules. These are atomic hydrogen, carbon, nitrogen and oxygen (H, C, N, O). Neon is also added to this sequence of targets as an isoelectronic atomic counterpart of water vapor, methane and ammonia molecules. The studied molecular targets are H2O (water vapor), CO (carbon-monoxide), CO2 (carbon-dioxide), CH4 (methane), C2H4 (ethylene), C2H6 (ethane), C4H10 (butane) as well as the DNA/RNA nucleobases C4H4N2O2 (uracil), C5H5N5 (adenine), C5H5N5O (guanine), C5H6N2O2 (thymine) and C4H5N3O (cytosine). The obtained total cross sections for any electronic target shell are compared with the available experimental data and overall favorable agreement is recorded at intermediate and high impact energies, which is the validity domain of the CDW method.