K-Shell Core-Electron Excitations in Electronic Stopping of Protons in Water from First Principles

Yi Yao, Dillon C. Yost, and Yosuke Kanai
Phys. Rev. Lett. 123, 066401 – Published 5 August 2019
PDFHTMLExport Citation

Abstract

Understanding the role of core-electron excitation in liquid water under proton irradiation has become important due to the growing use of proton beams in radiation oncology. Using a first-principles, nonequilibrium simulation approach based on real-time, time-dependent density functional theory, we determine the electronic stopping power, the velocity-dependent energy transfer rate from irradiating ions to electrons. The electronic stopping power curve agrees quantitatively with experimental data over the velocity range available. At the same time, significant differences are observed between our first-principles result and commonly used perturbation theoretic models. Excitations of the water molecules’ oxygen core electrons are a crucial factor in determining the electronic stopping power curve beyond its maximum. The core-electron contribution is responsible for as much as one third of the stopping power at the high proton velocity of 8.0 a.u. (1.6 MeV). K-shell core-electron excitations not only provide an additional channel for the energy transfer—they also significantly influence the valence electron excitations. In the excitation process, generated holes remain highly localized within a few angstroms around the irradiating proton path, whereas electrons are excited away from the path. In spite of their great contribution to the stopping power, K-shell electrons play a rather minor role in terms of the excitation density; only 1% of the hole population composes K-shell holes, even at the high proton velocity of 8.0 a.u. The excitation behavior revealed is distinctly different from that of photon-based ionizing radiation such as x or γ rays.

  • Figure
  • Figure
  • Figure
  • Figure
  • Received 12 February 2019
  • Revised 17 April 2019

DOI:https://doi.org/10.1103/PhysRevLett.123.066401

© 2019 American Physical Society

Physics Subject Headings (PhySH)

Accelerators & BeamsCondensed Matter, Materials & Applied Physics

Authors & Affiliations

Yi Yao, Dillon C. Yost, and Yosuke Kanai*

  • Department of Chemistry, University of North Carolina at Chapel Hill, North Carolina 27599, USA

  • *ykanai@unc.edu

Article Text (Subscription Required)

Click to Expand

Supplemental Material (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand
Issue

Vol. 123, Iss. 6 — 9 August 2019

Reuse & Permissions
Access Options
CHORUS

Article Available via CHORUS

Download Accepted Manuscript
Author publication services for translation and copyediting assistance advertisement

Authorization Required


×
×

Images

×

Sign up to receive regular email alerts from Physical Review Letters

Log In

Cancel
×

Search


Article Lookup

Paste a citation or DOI

Enter a citation
×