Liquid water radiolysis induced by secondary electrons generated from MeV-energy carbon ions

Hidetsugu Tsuchida; Tomoya Tezuka; Takeshi Kai; Yusuke Matsuya; Takuya Majima; Manabu Saito

doi:10.1063/5.0227465

Liquid water radiolysis induced by secondary electrons generated from MeV-energy carbon ions

J Chem Phys. 2024 Sep 14;161(10):104503. doi: 10.1063/5.0227465.

Authors

Hidetsugu Tsuchida^{1

2}, Tomoya Tezuka¹, Takeshi Kai³, Yusuke Matsuya^{3

4}, Takuya Majima¹, Manabu Saito^{1

2}

Affiliations

¹ Department of Nuclear Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8540, Japan.
² Quantum Science and Engineering Center, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan.
³ Nuclear Science and Engineering Center, Japan Atomic Energy Agency, 2-4 Shirakata, Tokai, Naka-gun, Ibaraki 319-1195, Japan.
⁴ Faculty of Health Sciences, Hokkaido University, Kita-12 Nishi-5, Kita-ku, Sapporo, Hokkaido 060-0812, Japan.

PMID: 39254164
DOI: 10.1063/5.0227465

Abstract

Fast ion beams induce damage to deoxyribonucleic acid (DNA) by chemical products, including secondary electrons, produced from interaction with liquid water in living cells. However, the production process of these chemical products in the Bragg peak region used in particle therapy is not fully understood. To investigate this process, we conducted experiments to evaluate the radiolytic yields produced when a liquid water jet in vacuum is irradiated with MeV-energy carbon beams. We used secondary ion mass spectrometry to measure the products, such as hydronium cations (H3O+) and hydroxyl anions (OH-), produced along with ·OH radicals, which are significant inducers of DNA damage formation. In addition, we simulated the ionization process in liquid water by incident ions and secondary electrons using a Monte Carlo code for radiation transport. Our results showed that secondary electrons, rather than incident ions, are the primary cause of ionization in water. We found that the production yield of H3O+ or OH- was linked to the frequency of ionization by secondary electrons in water, with these electrons having energies between 10.9 and 550 eV. These electrons are responsible for ionizing the outer-shell electrons of water molecules. Finally, we present that the elementary processes contribute to advancing radiation biophysics and biochemistry, which study the formation mechanism of DNA damage.