On the use of additivity rules to estimate electron production cross sections in proton-biomolecule collisions

Paredes, Sergio; Illescas, Clara; Méndez, L.

doi:10.1140/epjd/e2015-60106-8

Cited by 13 publications

(15 citation statements)

References 31 publications

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“…3 and appear to be somewhat lower than the electron-impact measurements of [25]. If we multiply the latter by a factor of 0.75 they almost perfectly match the proton data point at E = 1 MeV, which is well described by most of the theoretical calculations included in , IMM-AR [31]; experiments: Iriki11 [29,30], Rahman16 [25] for electron impact using equivelocity conversion, Rahman75% are the data of [25] multiplied by 0.75.…”

Section: Resultsmentioning

confidence: 52%

Electron capture and ionization cross-section calculations for proton collisions with methane and the DNA and RNA nucleobases

2019

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Net ionization and net capture cross-section calculations are presented for proton collisions from methane molecules and the DNA/RNA nucleobases adenine, cytosine, guanine, thymine, and uracil.We use the recently introduced independent-atom-model pixel counting method to calculate these cross sections in the 10 keV to 10 MeV impact energy range and compare them with results obtained from the simpler additivity rule, a previously used complete-neglect-of-differential-overlap method, and with experimental data and previous calculations where available. It is found that all theoretical results agree reasonably well at high energies, but deviate significantly in the low-to-intermediate energy range. In particular, the pixel counting method which takes the geometrical overlap of atomic cross sections into account is the only calculation that is able to describe the measurements for capture in proton-methane collisions down to 10 keV impact energy. For the nucleobases it also yields a significantly smaller cross section in this region than the other models. New measurements are urgently required to test this prediction.Collisions involving complex molecules pose a significant challenge to theory owing to their large number of degrees of freedom and their multi-center geometry. A convenient framework for a simplified discussion is offered by the independent atom model (IAM) according to which certain properties and quantities of a molecule are constitutive, i.e., can be obtained by adding up atomic contributions. When applied to collisions, the simplest version of the IAM consists in adding up the cross sections of the atomic constituents of a given molecule in order to obtain the molecular cross section. This procedure is usually referred to as the additivity rule (AR). It goes back to Bragg [1] and was first studied in a more systematic fashion in the 1950s for electron-impact ionization of medium-sized molecules [2]. The IAM-AR has since been applied to many electron-and ion-impact collision systems, typically with good success at high impact energies, while larger discrepancies with experimental data have been found in the low-to-intermediate energy region. This has been taken as an indication that molecular structure effects gain importance with decreasing collision energy [3].Accordingly, extensions and alternatives have been considered, such as ARs with weight factors (see, e.g., [4] and the review article [5] and references therein) and a completeneglect-of-differential-overlap (CNDO) approach (see, e.g., [3,6,7]. The latter starts from the assumption that a molecular net cross section can be expressed as a sum of partial cross sections for all initially occupied molecular orbitals (MOs) and then approximates those partial cross sections as linear combinations of atomic-orbital (AO) specific cross sections with weight factors that are obtained from a Mulliken population analysis [8]. In this way, the CNDO approach takes molecular structure information into account to some extent. However, CNDO cross sections do ...

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Section: Resultsmentioning

confidence: 52%

Electron capture and ionization cross-section calculations for proton collisions with methane and the DNA and RNA nucleobases

2019

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“…This is a desirable property since the IAM-AR is known to give fairly accurate results in the high-impact-energy regime in which capture and ionization cross sections are small and geometrical overlap is negligible. Toward lower energies, capture and ionization become stronger and the IAM-AR tends to overestimate experimental data [17,21]. In applications to proton collisions from medium-sized molecules such as H 2 O and from larger water, neon, and carbon clusters we have found that geometrical overlap does occur at these lower energies and leads to significant cross-section reductions [21,22].…”

Section: Introductionmentioning

confidence: 91%

“…Normally, atomic building blocks are used and the description is referred to as independent-atom-model (IAM)-AR. In a recent work it was argued that one can also start from small molecular constituents to assemble the ionization cross section of a larger molecule [17]. A caveat of this independent-molecule-model (IMM)-AR is that there are usually many different ways to decompose a given molecule into molecular building blocks and depending on which ansatz is used the resulting cross section may vary.…”

Section: Introductionmentioning

confidence: 99%

“…A caveat of this independent-molecule-model (IMM)-AR is that there are usually many different ways to decompose a given molecule into molecular building blocks and depending on which ansatz is used the resulting cross section may vary. It should also be noted that the IMM-AR work of [17] used experimental cross section data for the building blocks as input, while the atom-like contributions in the CNDO approach are usually obtained from perturbative collision calculations [16,[18][19][20].…”

Section: Introductionmentioning

confidence: 99%

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Proton-impact-induced electron emission from biologically relevant molecules studied with a screened independent atom model

Lüdde

Horbatsch

Kirchner

2019

J. Phys. B: At. Mol. Opt. Phys.

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We use the recently introduced independent-atom-model pixel counting method to calculate proton-impact net ionization cross sections for a large class of biologically relevant systems including pyrimidines, purines, amino acids, and nucleotides from 10 keV to 10 MeV impact energy. Overall good agreement with experimental data, where available, is found. A scaling prescription that involves coefficients derived from the independent atom model is shown to represent the cross section results better than scalings based on the number of (bonding) valence electrons of the target molecules. It is shown that the scaled net ionization cross sections of the proton-nucleotide collision systems can be represented in terms of a simple analytical formula with four parameters to within 3% accuracy.

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“…The paper of Hilgers et al [23] presents the results of a simulation of an ion-counting nanodosimeter. Theoretical studies of ionization of biomolecules with protons are reported by Paredes et al [24]. Finally, a theoretical analysis of secondary electron production in liquid water sensitized with carbon nanoparticles is reprorted by Verkhovtsev et al [9].…”

Section: Introductionmentioning

confidence: 99%

Nano-scale processes behind ion-beam cancer therapy

et al. 2016

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Abstract. This topical issue collates a series of papers based on new data reported at the third Nano-IBCT Conference of the COST Action MP1002: Nanoscale Insights into Ion Beam Cancer Therapy, held in Boppard, Germany, from October 27th to October 31st, 2014. The Nano-IBCT COST Action was launched in December 2010 and brought together more than 300 experts from different disciplines (physics, chemistry, biology) with specialists in radiation damage of biological matter from hadron-therapy centres, and medical institutions. This meeting followed the first and the second conferences of the Action held in October 2011 in Caen, France and in May 2013 in Sopot, Poland respectively. This conference series provided a focus for the European research community and has highlighted the pioneering research into the fundamental processes underpinning ion beam cancer therapy.

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On the use of additivity rules to estimate electron production cross sections in proton-biomolecule collisions

Cited by 13 publications

References 31 publications

Electron capture and ionization cross-section calculations for proton collisions with methane and the DNA and RNA nucleobases

Electron capture and ionization cross-section calculations for proton collisions with methane and the DNA and RNA nucleobases

Proton-impact-induced electron emission from biologically relevant molecules studied with a screened independent atom model

Nano-scale processes behind ion-beam cancer therapy

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