One electron-capture in collisions of fast nuclei with biomolecules of relevance to ion therapy

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This work is on total cross sections for single electron capture by protons from atomic and molecular targets. Most of the included atomic targets are also the constituents of the examined molecular targets. The latter targets are selected to be biomolecules. Computations are carried out using the continuum distorted wave (CDW) method at intermediate and high impact energies. First computed are atomic cross sections. These are subsequently employed to obtain molecular cross sections in the independent atom model (the Bragg additivity). Atomic targets are the backbone of DNA/RNA, i.e. hydrogen H, carbon C, nitrogen N and oxygen O. Also considered are neon Ne, argon Ar and krypton Kr. The studied molecular targets are H 2 , water vapor H 2 O, carbon monoxide CO, carbon dioxide CO 2 , methane CH 4 , ethylene C 2 H 4 , ethane C 2 H 6 , butane C 4 H 10 as well as the DNA/RNA nucleobases, uracil C 4 H 4 N 2 O 2 , adenine C 5 H 5 N 5 , guanine C 5 H 5 N 5 O, thymine C 5 H 6 N 2 O 2 and cytosine C 4 H 5 N 3 O. Neon atoms are isoelectronic with water molecules. This permits gaining some useful insights into the role of molecular forces by analyzing the cross sections for neon and water targets. The cross sections for each atomic target shell are summed up and compared with the available experimental data for atomic and molecular targets. The usefulness of the Bragg sum rule is assessed for molecular charge-exchange cross sections. Besides atomic physics, interest in this problem area exists also in heavy ion transport physics of relevance to plasma physics, astrophysics, the fusion program and radiotherapy. For example, in ion therapy, when the primary beam particles reach their deepest penetration distance, they release almost all their energy and this is biologically and clinically of utmost importance. In this targeted region, ions slow down abruptly and move with energies 20 keV/amu ≤ E ≤ 150 keV/amu. Therein, capture and loss of electrons are dominant energy loss mechanisms yielding maximum dose depositions. The present databases for electron capture cross sections can be used in Monte Carlo simulation of ion energy losses in matter, including tissue.