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Liljequist D. A model calculation of coherence effects in the elastic backscattering of very low energy electrons (1-20 eV) from amorphous ice. Int J Radiat Biol 2011; 88:50-3. [PMID: 21615241 DOI: 10.3109/09553002.2011.577506] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
PURPOSE Backscattering of very low energy electrons in thin layers of amorphous ice is known to provide experimental data for the elastic and inelastic cross sections and indicates values to be expected in liquid water. The extraction of cross sections was based on a transport analysis consistent with Monte Carlo simulation of electron trajectories. However, at electron energies below 20 eV, quantum coherence effects may be important and trajectory-based methods may be in significant error. This possibility is here investigated by calculating quantum multiple elastic scattering of electrons in a simple model of a very small, thin foil of amorphous ice. METHOD The average quantum multiple elastic scattering of electrons is calculated for a large number of simulated foils, using a point-scatterer model for the water molecule and taking inelastic absorption into account. The calculation is compared with a corresponding trajectory simulation. RESULTS The difference between average quantum scattering and trajectory simulation at energies below about 20 eV is large, in particular in the forward scattering direction, and is found to be almost entirely due to coherence effects associated with the short-range order in the amorphous ice. For electrons backscattered at the experimental detection angle (45° relative to the surface normal) the difference is however small except at electron energies below about 10 eV. CONCLUSION Although coherence effects are in general found to be strong, the mean free path values derived by trajectory-based analysis may actually be in fair agreement with the result of an analysis based on quantum scattering, at least for electron energies larger than about 10 eV.
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Affiliation(s)
- David Liljequist
- Department of Physics, Stockholm University, Albanova University Center, SE-106 91 Stockholm, Sweden.
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102
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103
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Balog R, Cicman P, Field D, Feketeová L, Hoydalsvik K, Jones NC, Field TA, Ziesel JP. Transmission and Trapping of Cold Electrons in Water Ice. J Phys Chem A 2011; 115:6820-4. [DOI: 10.1021/jp110475q] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Richard Balog
- Department of Physics and Astronomy, University of Aarhus, 8000 Aarhus C, Denmark
| | - Peter Cicman
- Department of Physics and Astronomy, University of Aarhus, 8000 Aarhus C, Denmark
| | - David Field
- Department of Physics and Astronomy, University of Aarhus, 8000 Aarhus C, Denmark
| | - Linda Feketeová
- Department of Physics and Astronomy, University of Aarhus, 8000 Aarhus C, Denmark
| | - Kristin Hoydalsvik
- Department of Physics and Astronomy, University of Aarhus, 8000 Aarhus C, Denmark
| | - Nykola C. Jones
- Institute for Storage Ring Facilities at Aarhus, University of Aarhus, 8000 Aarhus C, Denmark
| | - Thomas A. Field
- Department of Physics and Astronomy, Queen’s University Belfast, Belfast, BT7 1NN, United Kingdom
| | - Jean-Pierre Ziesel
- Laboratoire Collisions Agrégats Réactivité-IRSAMC, Université Paul Sabatier and CNRS-UMR 5589, 31062 Toulouse Cedex, France
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104
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Wiklund K, Fernández-Varea JM, Lind BK. A Monte Carlo program for the analysis of low-energy electron tracks in liquid water. Phys Med Biol 2011; 56:1985-2003. [DOI: 10.1088/0031-9155/56/7/005] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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105
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Liljequist D. Discussion of coherent and incoherent contributions to the spatial distribution of very low energy electrons elastically scattered in liquid water. Radiat Phys Chem Oxf Engl 1993 2011. [DOI: 10.1016/j.radphyschem.2010.08.014] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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106
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Friedland W, Dingfelder M, Kundrát P, Jacob P. Track structures, DNA targets and radiation effects in the biophysical Monte Carlo simulation code PARTRAC. Mutat Res 2011; 711:28-40. [PMID: 21281649 DOI: 10.1016/j.mrfmmm.2011.01.003] [Citation(s) in RCA: 236] [Impact Index Per Article: 18.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2010] [Revised: 01/18/2011] [Accepted: 01/22/2011] [Indexed: 01/08/2023]
Abstract
This review describes the PARTRAC suite of comprehensive Monte Carlo simulation tools for calculations of track structures of a variety of ionizing radiation qualities and their biological effects. A multi-scale target model characterizes essential structures of the whole genomic DNA within human fibroblasts and lymphocytes in atomic resolution. Calculation methods and essential results are recapitulated regarding the physical, physico-chemical and chemical stage of track structure development of radiation damage induction. Recent model extension towards DNA repair processes extends the time dimension by about 12 orders of magnitude and paves the way for superior predictions of radiation risks.
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Affiliation(s)
- Werner Friedland
- Helmholtz Zentrum München, German Research Center for Environmental Health, Institute of Radiation Protection, Ingolstädter Landstr. 1, 85764 Neuherberg, Germany.
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107
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Francis Z, Incerti S, Capra R, Mascialino B, Montarou G, Stepan V, Villagrasa C. Molecular scale track structure simulations in liquid water using the Geant4-DNA Monte-Carlo processes. Appl Radiat Isot 2011; 69:220-6. [DOI: 10.1016/j.apradiso.2010.08.011] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2009] [Revised: 08/06/2010] [Accepted: 08/12/2010] [Indexed: 11/30/2022]
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108
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Toburen LH, McLawhorn SL, McLawhorn RA, Carnes KD, Dingfelder M, Shinpaugh JL. Electron emission from amorphous solid water induced by passage of energetic protons and fluorine ions. Radiat Res 2010; 174:107-18. [PMID: 20681805 PMCID: PMC3835720 DOI: 10.1667/rr1984a.1] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Absolute doubly differential electron emission yields were measured from thin films of amorphous solid water (ASW) after the transmission of 6 MeV protons and 19 MeV (1 MeV/nucleon) fluorine ions. The ASW films were frozen on thin (1-microm) copper foils cooled to approximately 50 K. Electrons emitted from the films were detected as a function of angle in both the forward and backward direction and as a function of the film thickness. Electron energies were determined by measuring the ejected electron time of flight, a technique that optimizes the accuracy of measuring low-energy electron yields, where the effects of molecular environment on electron transport are expected to be most evident. Relative electron emission yields were normalized to an absolute scale by comparison of the integrated total yields for proton-induced electron emission from the copper substrate to values published previously. The absolute doubly differential yields from ASW are presented along with integrated values, providing single differential and total electron emission yields. These data may provide benchmark tests of Monte Carlo track structure codes commonly used for assessing the effects of radiation quality on biological effectiveness.
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Affiliation(s)
- L H Toburen
- Department of Physics, East Carolina University, Greenville, North Carolina 27858, USA.
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109
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110
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Brun E, Cloutier P, Sicard-Roselli C, Fromm M, Sanche L. Damage induced to DNA by low-energy (0-30 eV) electrons under vacuum and atmospheric conditions. J Phys Chem B 2009; 113:10008-13. [PMID: 19603845 DOI: 10.1021/jp902540k] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
In this study, we show that it is possible to obtain data on DNA damage induced by low-energy (0-30 eV) electrons under atmospheric conditions. Five monolayer films of plasmid DNA (3197 base pairs) deposited on glass and gold substrates are irradiated with 1.5 keV X-rays in ultrahigh vacuum and under atmospheric conditions. The total damage is analyzed by agarose gel electrophoresis. The damage produced on the glass substrate is attributed to energy absorption from X-rays, whereas that produced on the gold substrate arises from energy absorption from both the X-ray beam and secondary electrons emitted from the gold surface. By analysis of the energy of these secondary electrons, 96% are found to have energies below 30 eV with a distribution peaking at 1.4 eV. The differences in damage yields recorded with the gold and glass substrates is therefore essentially attributed to the interaction of low-energy electrons with DNA under vacuum and hydrated conditions. From these results, the G values for low-energy electrons are determined to be four and six strand breaks per 100 eV, respectively.
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Affiliation(s)
- Emilie Brun
- Laboratoire de Chimie Physique, CNRS UMR 8000, Université Paris-Sud 11, Bat. 350, 91405 Orsay Cedex, France
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111
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Nikjoo H, Emfietzoglou D, Charlton DE. The Auger effect in physical and biological research. Int J Radiat Biol 2009; 84:1011-26. [DOI: 10.1080/09553000802460172] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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112
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Can Monte Carlo track structure codes reveal reaction mechanism in DNA damage and improve radiation therapy? Radiat Phys Chem Oxf Engl 1993 2008. [DOI: 10.1016/j.radphyschem.2008.05.043] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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113
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Yabushita A, Hama T, Iida D, Kawanaka N, Kawasaki M, Watanabe N, Ashfold MNR, Loock HP. Release of hydrogen molecules from the photodissociation of amorphous solid water and polycrystalline ice at 157 and 193nm. J Chem Phys 2008; 129:044501. [DOI: 10.1063/1.2953714] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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114
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Liljequist D. A study of errors in trajectory simulation with relevance for 0.2–50eV electrons in liquid water. Radiat Phys Chem Oxf Engl 1993 2008. [DOI: 10.1016/j.radphyschem.2008.03.004] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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115
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Dingfelder M, Ritchie RH, Turner JE, Friedland W, Paretzke HG, Hamm RN. Comparisons of calculations with PARTRAC and NOREC: transport of electrons in liquid water. Radiat Res 2008; 169:584-94. [PMID: 18439039 DOI: 10.1667/rr1099.1] [Citation(s) in RCA: 93] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2007] [Accepted: 01/10/2008] [Indexed: 11/03/2022]
Abstract
Monte Carlo computer models that simulate the detailed, event-by-event transport of electrons in liquid water are valuable for the interpretation and understanding of findings in radiation chemistry and radiation biology. Because of the paucity of experimental data, such efforts must rely on theoretical principles and considerable judgment in their development. Experimental verification of numerical input is possible to only a limited extent. Indirect support for model validity can be gained from a comparison of details between two independently developed computer codes as well as the observable results calculated with them. In this study, we compare the transport properties of electrons in liquid water using two such models, PARTRAC and NOREC. Both use interaction cross sections based on plane-wave Born approximations and a numerical parameterization of the complex dielectric response function for the liquid. The models are described and compared, and their similarities and differences are highlighted. Recent developments in the field are discussed and taken into account. The calculated stopping powers, W values, and slab penetration characteristics are in good agreement with one another and with other independent sources.
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Affiliation(s)
- M Dingfelder
- Department of Physics, East Carolina University, Greenville, NC 27858, USA.
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116
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Dingfelder M, Travia A, McLawhorn RA, Shinpaugh JL, Toburen LH. Electron Emission from Foils and Biological Materials after Proton Impact. Radiat Phys Chem Oxf Engl 1993 2008; 77:1213-1217. [PMID: 19212448 PMCID: PMC2638064 DOI: 10.1016/j.radphyschem.2008.05.046] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Electron emission spectra from thin metal foils with thin layers of water frozen on them (amorphous solid water) after fast proton impact have been measured and have been simulated in liquid water using the event-by-event track structure code PARTRAC. The electron transport model of PARTRAC has been extended to simulate electron transport down to 1 eV by including low-energy phonon, vibrational and electronic excitations as measured by Michaud et al. (Radiat. Res. 159, 3-22, 2003) for amorphous ice. Simulated liquid water yields follow in general the amorphous solid water measurements at higher energies, but overestimate them significantly at energies below 50 eV.
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Affiliation(s)
- Michael Dingfelder
- Department of Physics, East Carolina University, Howell Science Complex, Greenville, NC 27858, USA
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117
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Zheng Y, Hunting DJ, Ayotte P, Sanche L. Radiosensitization of DNA by Gold Nanoparticles Irradiated with High-Energy Electrons. Radiat Res 2008; 169:19-27. [PMID: 18159957 DOI: 10.1667/rr1080.1] [Citation(s) in RCA: 124] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2007] [Accepted: 08/14/2007] [Indexed: 11/03/2022]
Affiliation(s)
- Yi Zheng
- Département de Chimie, Faculté des Sciences, , Université de Sherbrooke, Sherbrooke, Québec, Canada J1H 5N4.
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118
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Champion C, Zanotti-Fregonara P, Hindié E. CELLDOSE: A Monte Carlo Code to Assess Electron Dose Distribution—S Values for 131I in Spheres of Various Sizes. J Nucl Med 2007; 49:151-7. [DOI: 10.2967/jnumed.107.045179] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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119
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Swiderek P, Burean E. Analysis of band broadening in vibrational high-resolution electron-energy-loss spectra of condensed methane. J Chem Phys 2007; 127:214506. [PMID: 18067363 DOI: 10.1063/1.2802294] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
High-resolution vibrational electron-energy-loss spectra of multilayer condensed films of methane recorded at 20 K show a strong tailing of the vibrational bands that clearly exceeds the instrumental resolution. At low incident electron energy, this tailing is remarkably less important for the dipole-allowed bending vibration (nu(4)) than for other bands. Also, the tailing becomes less pronounced with increasing size of the molecule as demonstrated by spectra of ethane and heptane recorded under the same conditions. Dipole coupling, rotational broadening, and multiple inelastic scattering have been considered as origins of this band broadening. While the first two effects can be excluded, multiple scattering involving a low-frequency phonon band provides a reasonable explanation as demonstrated by simulations of the spectrum of methane using a classical two-stream model. A lower phonon frequency in the cases of the larger molecules is held responsible for the better resolved vibrational signals in the spectra of ethane and heptane.
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Affiliation(s)
- P Swiderek
- Fachbereich 2 (Chemie/Biologie), Universität Bremen, Leobener Strasse/NW 2, Postfach 330440, 28334 Bremen, Germany.
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120
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Emfietzoglou D, Nikjoo H. Accurate electron inelastic cross sections and stopping powers for liquid water over the 0.1-10 keV range based on an improved dielectric description of the Bethe surface. Radiat Res 2007; 167:110-20. [PMID: 17214512 DOI: 10.1667/rr0551.1] [Citation(s) in RCA: 102] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2006] [Accepted: 08/16/2006] [Indexed: 11/03/2022]
Abstract
Electron inelastic cross sections and stopping powers for liquid water over the 0.1-10 keV range are presented based on a recently developed dielectric response model for liquid water (D. Emfietzoglou, F. Cucinotta and H. Nikjoo, Radiat. Res. 164, 202-211, 2005) that is consistent with the experimental data over the whole energy-momentum plane. Both exchange and second-order Born corrections are included in a material-specific way using the dielectric functions of liquid water. The numerical results are fitted by simple analytic functions to facilitate their further use. Compared to previous studies, differential cross sections are shifted toward smaller energy losses resulting in smaller inelastic and stopping cross sections with differences reaching, on average, the approximately 20% and approximately 50% level, respectively. Contrary to higher energies, it is shown that the dispersion model for the momentum dependence of the dielectric functions (Bethe ridge) is as important as the optical model used. Within the accuracy of the experimental data (a few percent) upon which our dielectric model is based, the calculations are "exact" to first order, while the uncertainty of the results beyond first order is estimated at the 5-10% level. The present work overcomes the limitations of Bethe's theory at low energies by a self-consistent account of inner-shell effects and may serve to extend the ICRU electron stopping power database for liquid water down to 100 eV with a level of uncertainty similar to that for the higher-energy values.
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Affiliation(s)
- D Emfietzoglou
- Medical Physics Laboratory, University of Ioannina Medical School, Ioannina 451 10, Greece
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121
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122
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Elles CG, Jailaubekov AE, Crowell RA, Bradforth SE. Excitation-energy dependence of the mechanism for two-photon ionization of liquid H2O and D2O from 8.3to12.4eV. J Chem Phys 2006; 125:44515. [PMID: 16942164 DOI: 10.1063/1.2217738] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Transient absorption measurements monitor the geminate recombination kinetics of solvated electrons following two-photon ionization of liquid water at several excitation energies in the range from 8.3 to 12.4 eV. Modeling the kinetics of the electron reveals its average ejection length from the hydronium ion and hydroxyl radical counterparts and thus provides insight into the ionization mechanism. The electron ejection length increases monotonically from roughly 0.9 nm at 8.3 eV to nearly 4 nm at 12.4 eV, with the increase taking place most rapidly above 9.5 eV. We connect our results with recent advances in the understanding of the electronic structure of liquid water and discuss the nature of the ionization mechanism as a function of excitation energy. The isotope dependence of the electron ejection length provides additional information about the ionization mechanism. The electron ejection length has a similar energy dependence for two-photon ionization of liquid D(2)O, but is consistently shorter than in H(2)O by about 0.3 nm across the wide range of excitation energies studied.
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Affiliation(s)
- Christopher G Elles
- Department of Chemistry, University of Southern California, Los Angeles, California 90089, USA
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123
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Numerical simulation of multiple ionization and high LET effects in liquid water radiolysis. Radiat Phys Chem Oxf Engl 1993 2006. [DOI: 10.1016/j.radphyschem.2005.09.015] [Citation(s) in RCA: 122] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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124
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Affiliation(s)
- Bernd Winter
- Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max-Born-Strasse 2A, D-12489 Berlin, Germany.
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125
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Uehara S, Nikjoo H. Monte Carlo simulation of water radiolysis for low-energy charged particles. JOURNAL OF RADIATION RESEARCH 2006; 47:69-81. [PMID: 16571920 DOI: 10.1269/jrr.47.69] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
The paper describes the development of chemical modules simulating the prechemical and chemical stages of charged particle tracks in pure liquid water. These calculations are based on our physical track structure codes for electrons and ions (KURBUC, LEPHIST and LEAHIST) which provide the initial spatial distribution of H2O+, H2O* and subexcitation electrons at approximately 10(-15) s. We considered 11 species and 26 chemical reactions. A step-by-step Monte Carlo approach was adopted for the chemical stage between 10(-12) s and 10(-6) s. The chemistry codes enabled to simulate the non-homogeneous chemistry that pertains to electron, proton and alpha-particle tracks of various linear energy transfers (LET). Time-dependent yields of chemical species produced by electrons and ions of different energies were calculated. The calculated primary yields (G values at 10(-6) s) of 2.80 for OH and 2.59 for e(aq)- for 1 MeV electrons are in good agreement with the published values. The calculated G values at 10(-6) s for a wide range LETs from of 0.2 to 235 keV microm(-1) were obtained. The calculations show the LET dependence for OH and H2O2. The electron penetration ranges were calculated in order to discuss the role of low energy electrons.
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Affiliation(s)
- Shuzo Uehara
- School of Health Sciences, Kyushu University, Fukuoka, Japan.
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126
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Emfietzoglou D, Cucinotta FA, Nikjoo H. A complete dielectric response model for liquid water: a solution of the Bethe ridge problem. Radiat Res 2005; 164:202-11. [PMID: 16038591 DOI: 10.1667/rr3399] [Citation(s) in RCA: 128] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
We present a complete yet computationally simple model for the dielectric response function of liquid water over the energy-momentum plane, which, in contrast to earlier models, is consistent with the recent inelastic X-ray scattering spectroscopy data at both zero and finite momentum transfer values. The model follows Ritchie's extended-Drude algorithm and is particularly effective at the region of the Bethe ridge, substantially improving previous models. The present development allows for a more accurate simulation of the inelastic scattering and energy deposition process of low-energy electrons in liquid water and other biomaterials. As an example, we calculate the stopping power of liquid water for electrons over the 0.1-10 keV range where direct experimental measurements are still impractical and the Bethe stopping formula is inaccurate. The new stopping power values are up to 30-40% lower than previous calculations. Within the range of validity of the first Born approximation, the new values are accurate to within the experimental uncertainties (a few percent). At the low end, the introduction of Born corrections raises the uncertainty to perhaps approximately 10%. Thus the present model helps extend the ICRU electron stopping power database for liquid water down to about two orders of magnitude with a comparable level of uncertainty.
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Affiliation(s)
- Dimitris Emfietzoglou
- Medical Physics Laboratory, University of Ioannina Medical School, 451 10 Ioannina, Greece
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127
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Meesungnoen J, Jay-Gerin JP. High-LET Radiolysis of Liquid Water with 1H+, 4He2+, 12C6+, and 20Ne9+ Ions: Effects of Multiple Ionization. J Phys Chem A 2005; 109:6406-19. [PMID: 16833985 DOI: 10.1021/jp058037z] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Monte Carlo simulations are used to investigate the effects of multiple ionization of water molecules on the yields of formation of free radical and molecular species, including molecular oxygen, in the radiolysis of pure, deaerated liquid water by using different types of radiation (1H+, 4He2+, 12C6+, and 20Ne9+ ions) up to approximately 900 keV/microm, at neutral pH and 25 degrees C. Taking into account the double, triple, and quadruple ionizations of water, the primary (or "escape") yields (at 10(-6) s) of the various radiolytic species (G(e(aq)-), G(H*), G(H2), G(*OH), G(HO2*/O2*-), and G(H2O2) are calculated as a function of the linear energy transfer (LET) of the radiation. Our results quantitatively reproduce the large increase observed in G(HO2*/O2*-) at high LET. Under the conditions of this study, the mechanisms of triple and quadruple ionizations contribute only weakly to the production of HO2*/O2*-. With the exception of protons, our calculations also simultaneously predict a maximum in G(H2O2) corresponding to the LET of approximately 4.5-MeV helium ions (approximately 100 keV/microm) and approximately 110-MeV carbon ions (approximately 180 keV/microm). This maximum occurs where G(HO2*/O2*-) begins to rise sharply, suggesting, in agreement with previous experimental data, that the yields of HO2*/O2*- and H2O2 are closely linked. Moreover, our results show a steep increase in the initial and primary yields of molecular oxygen with increasing LET, giving support to the "oxygen in heavy-ion tracks" hypothesis. By contrast, it is found that, in the whole LET range considered, the incorporation of multiple ionization in the simulations has only little effect on the variation of our computed G(e(aq)-), G(H*), G(H2), and G(*OH) values as a function of LET. As expected, G(e(aq)-) and G(*OH) decrease continuously with increasing LET. G(H*) at first increases and then decreases at high LET. Finally, G(H2) monotonically rises with increasing LET. Our calculated yield values compare generally very well with experiment.
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Affiliation(s)
- Jintana Meesungnoen
- Département de Médecine Nucléaire et de Radiobiologie, Faculté de Médecine et des Sciences de la Santé, Université de Sherbrooke, 3001, 12 Avenue Nord, Sherbrooke (Québec) J1H 5N4, Canada
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128
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Gervais B, Beuve M, Olivera G, Galassi M, Rivarola R. Production of HO2 and O2 by multiple ionization in water radiolysis by swift carbon ions. Chem Phys Lett 2005. [DOI: 10.1016/j.cplett.2005.05.057] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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129
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Emfietzoglou D, Nikjoo H. The effect of model approximations on single-collision distributions of low-energy electrons in liquid water. Radiat Res 2005; 163:98-111. [PMID: 15606313 DOI: 10.1667/rr3281] [Citation(s) in RCA: 122] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
The development of cross sections for the inelastic interaction of low-energy electrons with condensed tissue-like media is best accomplished within the framework of the dielectric theory. In this work we investigate the degree to which various model approximations, used in the above methodology, influence electron single-collision distributions. These distributions are of major importance to Monte Carlo track structure codes, namely, the energy-loss spectrum, the inelastic inverse mean free path, and the ionization efficiency. In particular, we make quantitative assessment of the influence of (1) the optical data set, (2) the dispersion algorithm, and (3) the perturbation and exchange Born corrections. It is shown that, although the shape and position of the energy-loss spectrum remains almost fixed, its peak height may vary by up to a factor of 1.5. Discrepancies in the calculated inelastic inverse mean free path are largely within 20-30% above 100 eV; they increase drastically, though, at lower energies. Exchange and perturbation Born corrections increase gradually below 1 keV leading to a approximately 30 to 40% reduction of the inverse mean free path at 100 eV. The perturbation effect contributes more than the exchange effect to this reduction. Similar to the dispersion situation, the effect of Born corrections at lower energies is also unclear since the models examined disagree strongly below 100 eV. In comparison, the vapor data are higher than the liquid calculations by 20 to 50% as the energy decreases from 1 to 0.1 keV, respectively. The excitation contribution is the main cause of this difference, since the ionization efficiency in the liquid levels off at approximately 90%, whereas the plateau value for the vapor is approximately 70%. It is concluded that electron inelastic distributions for liquid water, although in some respects distinctively different from the vapor phase, have associated uncertainties that are comparable in magnitude to the phase differences. The situation below 100 eV is uncertain.
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Affiliation(s)
- Dimitris Emfietzoglou
- Medical Physics Laboratory, University of Ioannina Medical School, 451 10 Ioannina, Greece
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130
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Levesque PL, Michaud M, Sanche L. Absolute vibrational and electronic cross sections for low-energy electron (2–12 eV) scattering from condensed pyrimidine. J Chem Phys 2005; 122:094701. [PMID: 15836156 DOI: 10.1063/1.1854121] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Low-energy vibrational and electronic electron-energy-loss (EEL) spectra of pyrimidine condensed on a thin film of solid argon held at 18 K are reported for the incident-energy range of 2-12 eV. Sensitivity to symmetry and spin forbidden transitions as well as correlations to the triplet states of benzene make it possible to ascribe the main features, below 7 eV in the electronic part of the EEL spectrum, to triplet transitions. The lowest EEL feature with an energy onset at 3.5 eV is attributed to a transition to the (3)B(1)(n-->pi(*)) valence electronic state and the next triplet n-->pi(*) transition to a (3)A(2) state located around 4.5 eV. The remaining EEL features at 4.3, 5.2, 5.8, and 6.5 eV are all assigned to pi-->pi(*) transitions to states of symmetry (3)B(2), (3)A(1), (3)B(2), and (3)B(2)+(3)A(1), respectively. The most intense maximum at 7.6 eV is found to correspond to both (1)B(2) and (1)A(1) transitions, as in the vacuum ultraviolet spectra. Absolute inelastic cross sections per scatterer are derived from a single collision treatment described herein. Their values are found to lie within the 10(-17) cm(2) range for both the electronic and the vibrational excitations. Features in the energy dependence of the cross sections are discussed, whenever possible, by comparison with data and mechanisms found in the gas phase. A maximum over the 4-5 eV range is attributed to a B (2)B(1) shape resonance and another one observed in the 6-7 eV range is ascribed to either or both sigma(*) shape resonances of (2)A(1) and (2)B(2) symmetries.
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Affiliation(s)
- P L Levesque
- Groupe en Science des Radiations, Département de Médecine Nucléaire et Radiobiologie, Faculté de Médecine, Université de Sherbrooke, Sherbrooke, Québec J1H 5N4, Canada
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131
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Mozejko P, Bass AD, Parenteau L, Sanche L. Intrinsic and extrinsic factors in anion electron-stimulated desorption: D− from deuterated hydrocarbons condensed on Kr and water ice films. J Chem Phys 2004; 121:10181-9. [PMID: 15549893 DOI: 10.1063/1.1807813] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
The results of D(-) ion desorption induced by 3-20 eV electrons incident on condensed CD(4), C(2)D(6), C(3)D(8), C(2)D(4), and C(2)D(2) are presented. These compounds were deposited in submonolayer amounts on the surfaces of multilayer solid films of Kr and nonporous and porous amorphous ice. While desorption of the D(-) anions proceeds via well-known processes, i.e., dissociative electron attachment (DEA) and dipolar dissociation, significant perturbations of these processes due to presence of the different film substrates are observed. We have shown that it is possible to distinguish between the character and nature of these perturbations. The presence of the nonporous ice perturbs the D(-) desorption intensity by affecting the intrinsic properties of the intermediate anion states through which dissociation proceeds. On the other hand, the presence of the porous ice introduces extrinsic effects, which can affect electron energy losses prior to their interaction with the hydrocarbon molecule and/or the energies and intensities of the fragment species after dissociation. Simple mechanisms responsible for the observed variations in the intensities of desorbed anionic signals are proposed and discussed. Electron transfer from transient anion states to electron states of the substrate film or nearby hydrocarbon molecules appear as the most efficient mechanism to reduce the magnitude of the DEA process.
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Affiliation(s)
- Paweł Mozejko
- Groupe en Sciences des Radiations, Faculté de Medecine, Université de Sherbrooke, Sherbrooke, Québec J1H5N4 Canada.
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132
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Wilson WE, Miller JH, Lynch DJ, Lewis RR, Batdorf M. Analysis of Low-Energy Electron Track Structure in Liquid Water. Radiat Res 2004; 161:591-6. [PMID: 15161364 DOI: 10.1667/rr3179] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
An implementation is presented of interaction cross sections for non-relativistic electron track structure simulations. The model, incorporating liquid-phase cross sections for inelastic interactions and improved algorithms for elastic scattering, is applied to Monte Carlo simulation of the track structure of low-energy electrons. Benchmark distributions and mean values are presented for several measures of penetration distances that characterize the general physical extent of the track structure. The results indicate that, except for the last approximately 500 eV of energy loss, electron tracks have a quasi-linear character; this suggests that a major part of an electron track may be reasonably described by a lineal-energy-like characterization.
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Affiliation(s)
- W E Wilson
- School of Electrical Engineering and Computer Science, Washington State University, Richland, Washington 99352, USA.
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133
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134
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Cho W, Michaud M, Sanche L. Vibrational and electronic excitations of H[sub 2]O on thymine films induced by low-energy electrons. J Chem Phys 2004; 121:11289-95. [PMID: 15634084 DOI: 10.1063/1.1814057] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
We investigated vibrational and electronic excitations of 0.1-layer up to 2.4-layer film of H(2)O deposited on a 1.4-layer film of thymine condensed on Ar at a temperature of 18 K using high-resolution electron-energy loss (EEL) spectroscopy at the incident energy of 12 eV. The spectral contribution originating essentially from the H(2)O overlayer is obtained by separating the measured contribution from the underlying film of thymine, considering the electron beam attenuation in the H(2)O overlayer. The vibrational EEL spectrum of submonolayer amount of H(2)O on thymine, which excepts for small energy shift of the vibrational bands, is found to compare in intensity to that of the same amount of H(2)O deposited directly on the argon. The electronic energy-loss intensity near 8.6 eV, which is attributed to the excitation of (3,1)B(1) states of H(2)O in condensed phase, is observed to decrease by a factor of about 3 by the presence of the underlying film of thymine. This indicates that the corresponding cross section for excitation the (3,1)B(1) states of H(2)O by the electron impact is reduced significantly by the close proximity of the thymine molecules.
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Affiliation(s)
- W Cho
- Département de Médecine Nucléaire et Radiobiologie, Faculté de Médecine, Université de Sherbrooke, Sherbrooke, Québec J1H 5N4, Canada
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135
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Faradzhev NS, Perry CC, Kusmierek DO, Fairbrother DH, Madey TE. Kinetics of electron-induced decomposition of CF[sub 2]Cl[sub 2] coadsorbed with water (ice): A comparison with CCl[sub 4]. J Chem Phys 2004; 121:8547-61. [PMID: 15511180 DOI: 10.1063/1.1796551] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
The kinetics of decomposition and subsequent chemistry of adsorbed CF(2)Cl(2), activated by low-energy electron irradiation, have been examined and compared with CCl(4). These molecules have been adsorbed alone and coadsorbed with water ice films of different thicknesses on metal surfaces (Ru; Au) at low temperatures (25 K; 100 K). The studies have been performed with temperature programmed desorption (TPD), reflection absorption infrared spectroscopy (RAIRS), and x-ray photoelectron spectroscopy (XPS). TPD data reveal the efficient decomposition of both halocarbon molecules under electron bombardment, which proceeds via dissociative electron attachment (DEA) of low-energy secondary electrons. The rates of CF(2)Cl(2) and CCl(4) dissociation increase in an H(2)O (D(2)O) environment (2-3x), but the increase is smaller than that reported in recent literature. The highest initial cross sections for halocarbon decomposition coadsorbed with H(2)O, using 180 eV incident electrons, are measured (using TPD) to be 1.0+/-0.2 x 10(-15) cm(2) for CF(2)Cl(2) and 2.5+/-0.2 x 10(-15) cm(2) for CCl(4). RAIRS and XPS studies confirm the decomposition of halocarbon molecules codeposited with water molecules, and provide insights into the irradiation products. Electron-induced generation of Cl(-) and F(-) anions in the halocarbon/water films and production of H(3)O(+), CO(2), and intermediate compounds COF(2) (for CF(2)Cl(2)) and COCl(2), C(2)Cl(4) (for CCl(4)) under electron irradiation have been detected using XPS, TPD, and RAIRS. The products and the decomposition kinetics are similar to those observed in our recent experiments involving x-ray photons as the source of ionizing irradiation.
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Affiliation(s)
- N S Faradzhev
- Department of Physics and Astronomy, and Laboratory for Surface Modification, Rutgers, The State University of New Jersey, Piscataway, NJ 08854-8019, USA
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Meesungnoen J, Filali-Mouhim A, Ayudhya NSN, Mankhetkorn S, Jay-Gerin JP. Multiple ionization effects on the yields of HO2/O2− and H2O2 produced in the radiolysis of liquid water with high-LET 12C6+ ions: a Monte-Carlo simulation study. Chem Phys Lett 2003. [DOI: 10.1016/s0009-2614(03)01101-1] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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