Stopping cross-sections of liquid water for 0.3–2.0 MeV protons

Shimizu, Morihito; Hayakawa, T.; Kaneda, Mizuho; Tsuchida, H.; Itoh, Akio

doi:10.1016/j.vacuum.2009.11.019

Cited by 28 publications

(44 citation statements)

References 17 publications

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“…These technical, but important, details are discussed in the Supplemental Material, in addition to comparisons to our earlier work 18 , which did not consider core electron effects.The calculated stopping power as a function of the proton velocity ranging from 0.5 to 8 a.u. (corresponding to the kinetic energy of 6.2 keV-1.6 MeV) is compared to the available experimental stopping power data [36][37] and to the so-called SRIM 16 model in Figure 1. The only experimental data available in this velocity range are the measurements by Shimizu, et al [36][37] .…”

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

2019

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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 firstprinciples, non-equilibrium 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 but 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 its 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 comprises K-shell holes even at the high proton velocity of 8.0 a.u.. The excitation behavior revealed here is distinctly different from that of photonbased ionizing radiation such as X/γ-rays.When a highly energetic ion travels through and interacts with matter, its kinetic energy is transferred into the target material's electronic and nuclear subsystems. This energy loss of the projectile ion can arise from both elastic collisions with nuclei (nuclear stopping) and inelastic scattering events (electronic stopping). When the particle's kinetic energy is sufficiently large (on the order of ~10 keV per nucleon), the major contribution to the energy transfer comprises electronic stopping wherein the projectile ion induces massive electronic excitations in the target matter 1-2 . This electronic stopping phenomenon is at the heart of emerging ion bean cancer therapies. The use of proton beam radiation over more conventional radiation based on X/γ-ray photons is often considered more effective because of the ion's distinct spatial energy deposition profile with a very sharp peak. [3][4] By calibrating the initial kinetic energy of the protons, this energy deposition peak can be tuned to coincide with the location of the tumour. This energy deposition profile is largely determined by electronic stopping power, which measures the rate of energy transfer from the charged particle to electrons in matter per unit distance of the energetic particle's movement. 1,[5][6][7] The stopping power is a continuous function of the particle velocity, and the velocities near the...

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“…Electronic stopping power curve from our firstprinciples simulation, in comparison to the experimental data by Shimizu et al[36][37] (Sz10), SRIM16 model, the Bethe model 40 with I=78 eV recommended by International Commission on Radiation Units and Measurement8 , and the Emfietzoglou's model[10][11][12] .…”

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

2019

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“…a r t i c l e i n f o et al [1,2] at Kyoto (Japan), and by Siiskonen et al [3] at Jyväskylä 34 (Finland). In the Kyoto method, the stopping power was not mea- in the collection of stopping data graphs by one of us [6].…”

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Comments on recent measurements of the stopping power of liquid water

García-Molina

Abril

Vera

et al. 2013

Nuclear Instruments and Methods in Physics Research Section B:

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“…There are two recent experimental stopping power results for protons in liquid water: measurements by Shimizu et al 2,3 at Kyoto, and by Siiskonen et al 4 at Jyväskylä (Finland). In the Kyoto method, the stopping power was not measured directly, but scattering from a liquid water jet target (diameter 50 μm) was measured at various angles, and the scattering distributions were compared to distributions calculated by means of GEANT Monte Carlo simulations; the diameter D of the liquid water target and a correction factor multiplying SRIM stopping were used as fitting parameters.…”

Section: The Stopping Power Of Liquid Watermentioning

confidence: 99%