Relation between biomolecular dissociation and energy of secondary electrons generated in liquid water by fast heavy ion
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THE EUROPEAN PHYSICAL JOURNAL D
Regular Article
Relation between biomolecular dissociation and energy of secondary electrons generated in liquid water by fast heavy ions? Hidetsugu Tsuchida1,2,a , Takeshi Kai3 , Kensei Kitajima4 , Yusuke Matsuya3 , Takuya Majima2 , and Manabu Saito1,2 1 2 3
4
Quantum Science and Engineering Center, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan Department of Nuclear Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8530, Japan Nuclear Science and Engineering Center, Research Group for Radiation Transport Analysis, Japan Atomic Energy Agency (JAEA), Tokai, Ibaraki 319-1195, Japan Institute of Low Temperature Science, Hokkaido University, Sapporo, Hokkaido 060-0819, Japan Received 23 March 2020 / Received in final form 31 July 2020 / Accepted 21 September 2020 Published online 13 October 2020 c EDP Sciences / Societ`
a Italiana di Fisica / Springer-Verlag GmbH Germany, part of Springer Nature, 2020 Abstract. In this work, we measured and simulated the dissociation of biomolecules in liquid water induced by secondary electrons ejected from water molecules during fast heavy-ion irradiation. We calculated the energy spectra of secondary electrons generated along carbon ion tracks in liquid water in the Bragg peak region. The calculation was done using the Particle and Heavy Ion Transport code System (PHITS) in carbon track structure mode. This mode enables simulation of inelastic collisions along a carbon ion track based on the cross sections considered in the Monte Carlo code KURBUC. To understand the biomolecular dissociation processes in our previous MeV-SIMS experiments with microdroplet targets of glycine solution, we calculated the collision spectra of secondary electrons produced near liquid surfaces using PHITS. Furthermore, we examined the relationship between the secondary electron energy and formation of positive and negative glycine fragments. The results showed that the formation of methylene amine cations is caused by secondary electrons with energies of 13–100 eV. The formation of glycine-related negative ions such as cyanide anion, formate anion, and deprotonated glycine was found to be caused by low-energy (less than 13 eV) secondary electrons. These ions are known products of dissociative electron attachment.
1 Introduction The role of secondary electrons in radiation damage to biological matter is currently a topic of interest in radiation biophysics, chemistry, and biology and is relevant to charged particle cancer therapy [1]. Interaction of ionizing radiation with living tissue involves deposition of energy into the biomolecular structure of living cells. Because water is the most abundant molecule in cells, accounting for at least 70% of all molecules in cells, the radiation primarily interacts with water molecules surrounding DNA in cells. The energy of the radiation is transferred to the water. Radiation such as fast heavy ions releases extremely high energy into tracks with nanometer-size volumes. The secondary electrons generated typically hav
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