1,502 research outputs found
Comprehensive track-structure based evaluation of DNA damage by light ions from radiotherapy-relevant energies down to stopping.
No full textTrack structures and resulting DNA damage in human cells have been simulated for hydrogen, helium, carbon, nitrogen, oxygen and neon ions with 0.25-256 MeV/u energy. The needed ion interaction cross sections have been scaled from those of hydrogen; Barkas scaling formula has been refined, extending its applicability down to about 10 keV/u, and validated against established stopping power data. Linear energy transfer (LET) has been scored from energy deposits in a cell nucleus; for very low-energy ions, it has been defined locally within thin slabs. The simulations show that protons and helium ions induce more DNA damage than heavier ions do at the same LET. With increasing LET, less DNA strand breaks are formed per unit dose, but due to their clustering the yields of double-strand breaks (DSB) increase, up to saturation around 300 keV/μm. Also individual DSB tend to cluster; DSB clusters peak around 500 keV/μm, while DSB multiplicities per cluster steadily increase with LET. Remarkably similar to patterns known from cell survival studies, LET-dependencies with pronounced maxima around 100-200 keV/μm occur on nanometre scale for sites that contain one or more DSB, and on micrometre scale for megabasepair-sized DNA fragments
Stochastic aspects and uncertainties in the prechemical and chemical stages of electron tracks in liquid water: a quantitative analysis based on M. C. simulations
No full textStochastic aspects and uncertainties in the prechemical and chemical stages of electron tracks in liquid water: A quantitative analysis based on Monte Carlo simulations.
No full textA new physical module for the biophysical simulation code PARTRAC has recently been developed, based on newly derived electron inelastic-scattering cross-sections in liquid water. In the present work, two modules of PARTRAC describing the production, diffusion and interaction of chemical species were developed with the specific purpose of quantifying the role of the uncertainties in the parameters controlling the early stages of liquid water radiolysis. A set of values for such parameters was identified, and time-dependent yields and frequency distributions of chemical species produced by electrons of different energies were calculated. The calculated yields were in good agreement with available data and simulations, thus confirming the reliability of the code. As the primary-electron energy decreases down to 1 keV, the *OH decay kinetics were found to get faster, reflecting variations in the spatial distribution of the initial energy depositions. In agreement with analogous works, an opposite trend was found for energies of a few hundred eV, due to the very small number of species involved. The spreading effects shown at long times by *OH frequency distributions following 1 keV irradiation were found to be essentially due to stochastic aspects of the chemical stage, whereas for 1 MeV tracks the physical and pre-chemical stages also were found to play a significant role. Relevant differences in the calculated e(aq) -yields were found by coupling the physics of PARTRAC with descriptions of the pre-chemical and chemical stages adopted in different models. This indicates a strict interrelation of the various stages, and thus a strong dependence of the parameter values on the assumptions made for the preceding and subsequent stages of the process. Although equally acceptable results can be obtained starting from different assumptions, it is necessary to keep control of such uncertainties, since they can significantly influence the modeling of radical attack on DNA and, more generally, radiobiological damage estimation. This study confirms the need for new, independently derived data on specific steps of water radiolysis, to be included in comprehensive biophysical simulation codes
Cross-section scaling for track structure simulations of low-energy ions in liquid water.
No full textRadiation damage by low-energy ions significantly contributes to the high biological efficiency of ion beams in distal Bragg peak regions as well as to the energy-dependent efficiency of neutron irradiation. To enable assessing biological effects of ions at energies <1 MeV u−1 with track-structure based models, a Barkas-like scaling procedure is developed that provides ion cross sections in liquid water based on those for hydrogen ions. The resulting stopping power and range for carbon ions agree with the ICRU 73 database and other low-energy stopping power data. The method represents the basis for extending PARTRAC simulations of light ion track structures and biological effects down to the keV u−1 range
Dingfelder, George (Death, 1891-05-17)
No full textAddress: 11 Melanchton St.Age at death: 41332/Pg 58/1891/M W M/Ohio/Dr. Samuel Nickles/Schreiber/Carthage RoadOriginal record filed in drawer labeled 'DIETZ-DOERGER'
Dingfelder, John (Death, 1897-03-01)
No full textAddress: 1736 Tecumseh St.Age at death: 77 yrs.Pg 21/1897/27/M W M/Germany/Dr. T.F. Dickinson/Geo. H.High/Spring GroveOriginal record filed in drawer labeled 'DIETZ-DOERGER'
CMOS MAPS upgrade for the Belle II Vertex Detector
No full texthttp://dx.doi.org/10.13039/100018693 Horizon 2020http://dx.doi.org/10.13039/501100003359 Generalitat Valencian
SU‐E‐T‐334: Track Structure Simulations of Charged Particles at Low and Intermediate Energies: Cross Sections Needs for Light and Heavy Ions
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The Bethe surface of liquid water.
No full textThe Bethe surface of liquid water, earlier calculated using a semi-empirical model, is compared with recent available data from IXS-experiments (inelastic X-ray scattering; Compton scattering of high energy photons) in liquid water. No alarming discrepancy is found on a global view of the Bethe surface. The extrapolation to the optical limit (viz., at zero momentum transfer) is shown and the reliability of these data is discussed in detail
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