Regular Article

Relation between biomolecular dissociation and energy of secondary electrons generated in liquid water by fast heavy ions^★

¹ Quantum Science and Engineering Center, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan
² Department of Nuclear Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8530, Japan
³ Nuclear Science and Engineering Center, Research Group for Radiation Transport Analysis, Japan Atomic Energy Agency (JAEA), Tokai, Ibaraki 319-1195, Japan
⁴ Institute of Low Temperature Science, Hokkaido University, Sapporo, Hokkaido 060-0819, Japan

^a e-mail: tsuchida@nucleng.kyoto-u.ac.jp

Received: 23 March 2020
Received in final form: 31 July 2020
Accepted: 21 September 2020
Published online: 13 October 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.