Total cross sections for electrons and positrons colliding with H<sub>2</sub>O molecules

Sueoka, Osamu; Mori, Shigeki; Katayama, Yoshifumi

doi:10.1088/0022-3700/19/10/008

Cited by 92 publications

(107 citation statements)

References 8 publications

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“…Considering the direct measurements of σ T first, the discrepancy between the present and previous determinations [11,[13][14][15] is evident across the whole energy range; for instance the current measurement being a factor of 1.4-2 higher at 10 eV. Two theoretical predictions of σ T are shown in Fig.…”

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confidence: 54%

“…However, polarization often enhances direct ionization by positrons, so that they can be more penetrating and more ionizing than electrons, a result of potential import in analyses of astrophysical (e.g., [8]) and atmospheric events (e.g., [9]) as well as in positron-track simulations for dosimetry in positron emission tomography (e.g., [10]). In turn, these studies contribute to the motivation for investigating the interaction of e þ with water which accounts for about 60% of the human body and which is the most abundant greenhouse gas in the atmosphere.Measurements of positron-water total cross section (σ T ) were first carried out 30 years ago [11,12]. Since then, only a few new results have been added, experimentally [13][14][15] and theoretically [16,17], without a satisfactory agreement emerging among them.…”

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confidence: 99%

“…Detection of FSPs leads to a systematic underestimate of the beam attenuation and, thus, the measured total cross sections. In this respect, beams that employ magnetic fields are more likely to transport FSPs from the interaction region to the detector, with a dependence of σ T upon the magnetic field strength persisting even for weak fields (e.g., ≃4-9 Gauss [11,12]). This type of systematic effect can be reduced by using electrostatic beams which enable both the interaction and detection regions to be field free, thus, facilitating the attainment of a smaller (energy-independent) angular acceptance [25][26][27].…”

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confidence: 99%

“…Measurements of positron-water total cross section (σ T ) were first carried out 30 years ago [11,12]. Since then, only a few new results have been added, experimentally [13][14][15] and theoretically [16,17], without a satisfactory agreement emerging among them.…”

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confidence: 99%

“…In these ranges, the measurements are, respectively, ≃20% higher and ≃15% lower than the theories. [11,28]; filled star, Zecca et al [13]; filled triangle, Beale et al [14]. (b) present σ T results compared with theories: (dasheddotted line) SCOP [16]; (long dashed line) IAM-SCAR [17].…”

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confidence: 99%

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High-Resolution Measurements of e++H2O Total Cross Section

et al. 2016

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Using a purely electrostatic positron beam, the total cross section of positrons scattering from H 2 O has been measured for the first time with a high angular discrimination (≃1°) against forward scattered projectiles. Results are presented in the energy range (10-300) eV. Significant deviations from previous measurements are found which are, if ascribed entirely to the angular acceptances of various experimental systems, in quantitative accord with ab initio theoretical predictions of the differential elastic scattering cross section. DOI: 10.1103/PhysRevLett.117.253401 While the apparent imbalance between matter and antimatter in the Universe remains a major puzzle in science [1,2], much progress in the understanding of the interactions between the two has been achieved through studies of controlled collisions of positrons ðe þ Þ and positronium (Ps, the short-lived atom made of an electron and a positron) with atoms and molecules [3][4][5][6][7].At low energies, the static and polarization interactions tend to cancel for positrons reducing their scattering probability in comparison with electrons. However, polarization often enhances direct ionization by positrons, so that they can be more penetrating and more ionizing than electrons, a result of potential import in analyses of astrophysical (e.g., [8]) and atmospheric events (e.g., [9]) as well as in positron-track simulations for dosimetry in positron emission tomography (e.g., [10]). In turn, these studies contribute to the motivation for investigating the interaction of e þ with water which accounts for about 60% of the human body and which is the most abundant greenhouse gas in the atmosphere.Measurements of positron-water total cross section (σ T ) were first carried out 30 years ago [11,12]. Since then, only a few new results have been added, experimentally [13][14][15] and theoretically [16,17], without a satisfactory agreement emerging among them. The integral (σ el ) and differential (dσ el =dΩ) elastic (el) scattering cross sections for e þ þ H 2 O have also been measured recently [17], complementing theoretical determinations [18,19].Because of the long-range forces involved in the scattering of charged projectiles from a polar molecule such as H 2 O, one of the major difficulties in measuring σ T (even in the case of electrons, e.g., [20][21][22][23]) lies in discriminating against the considerable flux of small forward-angle scattered particles (FSPs) (e.g., [16,19]). The largest error associated with FSPs arises from elastic scattering and rovibrational inelastic processes which cannot be easily distinguished from the incident flux via energy loss discrimination since this is smaller than (or comparable to) typical beam energy resolutions (e.g., the first vibrational excitation from the ground state J ¼ 0 is ≃1595 cm −1 [24]). Detection of FSPs leads to a systematic underestimate of the beam attenuation and, thus, the measured total cross sections. In this respect, beams that employ magnetic fields are more likely to transport FSPs from the...

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confidence: 54%

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confidence: 99%

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confidence: 99%

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confidence: 99%

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confidence: 99%

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High-Resolution Measurements of e++H2O Total Cross Section

et al. 2016

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Positron Scattering: Total Elastic and Grand Total Cross Sections for Molecules of Astrophysical Importance

2019

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Spherical complex optical potential (SCOP) method, appropriately modified by our group for positron scattering, is employed to compute total elastic and grand total cross sections for astrophysical molecules. The cross sections for the present targets, viz. H2O, NH3, HCl, OCS and SO2 are reported for a wide energy range, spanning from 1 eV to 5000 eV. The elastic cross sections for HCl and OCS are reported for the first time. In the intermediate to high energy regime, results of most of the targets studied compare fairly well with the recent measurements, wherever available. Present cross sections would be useful for modelling astrophysical systems.

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