By a historical overview, we show the importance of a laconic paper by Kolos and Wolniewicz dating to 1962 Phys. Lett. 5(2), 222-223 (1962), in which they applied the variational method for the ...hydrogen molecule. In the first part of this perspective (say till 1996), the experiments on electron molecule scattering (including hydrogen) developed a vast range of techniques, even if the results were far from being congruent Riv. Nuovo Cimento 19/3, 1996. In turn, in the last years, we have observed the quickly rising applicability of theoretical methods, like convergent-close coupling Zammit et al. Phys. Rev. Lett. 116, 233201 (2016) and R-matrix Meltzer & Tennyson, J. Phys. Phys. B 53, 245203 (2020). The mutual agreement between theories and experiments allows defining recommended cross-sections for electron and positron scattering from zero to sub-relativistic energies. This, in turn, enables to check the dispersion relation, i.e. the interdependence between the zero-energy integral elastic, the high-energy elastic differential at zero angle, and the integral of the total cross-section from zero to infinity. Such a relation holds, within the experimental uncertainties, for positrons. For electrons, a big discrepancy points to the importance of the exchange effects in the e
H
scattering.
Positron annihilation techniques, being non-destructive, allowing depth profiling down to a few micrometers and detecting open-volume defects (vacancies, dislocations etc.) at single ppm ...concentrations constitute a valuable and complementary method, compared to other solid-state-physics studies. We give examples of investigation in the field of semiconductors with different techniques, both with and without use of positron low-energy beams. The Doppler broadening of the 511keV annihilation line method and the slow positron beam were used to study helium-implanted silicon and the surface reduction processes in semiconducting glasses. The positron lifetime technique and coincidence spectra of the Doppler broadening were used for systematic studies of metals and semiconductors. Doppler-coincidence method was then used to identify the kinetics of oxygen precipitates in Czochralski-grown silicon.
Abstract
In this paper we will describe didactic elements in the Horizon 2020 project FCHgo. This project is directed at children and adolescents between 8 and 18 years old. Its ultimate goal is to ...raise awareness for renewable energy sources, in particular hydrogen as a fuel and fuel cells for electric power. As part of the project, we are developing a toolkit for teachers and pupils, based upon a narrative approach to physical science and engineering. We believe the narrative approach to be best suited for this project because it allows us to take into account the cognitive tools available to pupils at various stages of their development.
Protonated water clusters Wróblewski, T.; Karwasz, G. P.
The European physical journal. ST, Special topics,
10/2013, Letnik:
222, Številka:
9
Journal Article, Conference Proceeding
Recenzirano
A complete set of protonated water clusters conformers up to
n
= 8 have been evaluated by ab-initio Hartree-Fock method in 6-311G** molecular orbitals basis set and with quadratic complete basis set ...method. Configurations of ground-state conformers are in a good accord with those available in literature but present dissociation energies for the light clusters agree better with experimental values. A tentative analysis of experimental conditions for observation of certain clusters is presented in comparison to selected formation paths of clusters. Dissociation energies show a broad range of values.
Doppler-broadening measurements of the electron–positron annihilation line in twenty-seven single-element samples are presented. A coincidence technique has been used to suppress the background and ...to evidence the contribution of positron annihilation with core electrons. Systematic dependences on the atomic number of the target material are found in ratio curves obtained dividing the measured spectra by the spectrum of a reference material. The positron lifetime technique has been used to detect the presence of positron traps in all the samples. The change in the high-momentum part of the annihilation line due to positron trapping is illustrated. The measured data are in a good qualitative agreement with recent theoretical calculation and constitute the most complete measurement series, up to now, to establish a future data-base for positron annihilation spectroscopy.
Coincidence Doppler broadening spectra measurements on B-doped and undoped single and polycrystalline Ni3Al alloys exhibit characteristic differences. The probability of the positron-3d electron ...annihilations decreases with the increase of B concentration in single crystals of Ni3Al alloys, while it increases with B concentration in polycrystals of Ni3Al alloys, as long as the concentration of B is less than its solubility limit. The behavior of positrons and B atoms in single and polycrystals of Ni3Al alloys has been discussed.
New experiments on the very low-energy electron and positron scattering allow to verify the old question on applicability of modified effective range theory (MERT). We perform it using an analytical ...solution of the Schrödinger equation with the long-range polarization potential. In this work two atomic (He, Ar) and molecular (H
2
, CH
4
) target are studied using this approach. Total cross sections were used for obtaining parameters characterizing the scattering phase shifts related to the short-range interaction potential; differential cross sections were used for comparison. Differently from previous works, we conclude that MERT with few (2-3) partial waves applies very well up to energies of few eV in all four targets studied. For positrons, reliable experimental data indicate occurrence of zeros in the
s
-wave phase shifts for all four targets. This should be recognized as Ramsauer-Townsend minima.
Buried nanocavities at about 350 nm depth in Si were produced by thermal treatment of He implanted p-type (100) Si. The internal surfaces of the nanocavities were found free of impurity decorations ...by examining the high-momentum part of the Doppler-broadened positron annihilation spectra. Positron lifetime measurements with a pulsed slow positron beam show neither a short lifetime (125-150 ps) ascribable to parapositronium nor a longer lifetime (2-4 ns) ascribable to pick-off annihilation of orthopositronium. The lifetime of positrons trapped into nanocavities was found to be about 500 ps. The absence of positronium formation could be explained by an insufficient electron density and a lack of electron states in the band gap at the nanocavities internal surfaces produced in the p-type silicon.
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