arXiv subjects

Sergey V. Stepanov

Publications and source records attributed to Sergey V. Stepanov.

5 recordsLinked to original sources

arXiv2012

Positronium in a liquid phase: formation, bubble state and chemical reactions

This chapter reviews the following items: 1. Energy deposition and track structure of fast positrons: ionization slowing down, number of ion-electron pairs, typical sizes, thermalization, electrostatic interaction between e+ and its blob, effect of local heating; 2. Positronium formation in condensed media: the Ore model, quasifree Ps state, intratrack mechanism of Ps formation; 3. Fast intratrack diffusion-controlled reactions: Ps oxidation and ortho-para conversion by radiolytic products, reaction rate constants, interpretation of the PAL spectra in water at different temperatures; 4. Ps bubble models. "Non-point" positronium: wave function, energy contributions, relationship between the pick-off annihilation rate and the bubble radius.

cond-mat.other↗

arXiv2012

Beyond the Point Ps Approximation

In application to positron annihilation spectroscopy, Ps atom is considered not as a point particle, but as a finite size e+ e- pair localized in a bubble-state in a medium. Variation of the internal Coulombic e+ -e- attraction vs. the bubble radius is estimated.

cond-mat.other↗

arXiv2012

Effects of local heating and premelting in the terminal part of the e$^+$ track

Due to the ionizations promoted by the slowing down of energetic positron and subsequent ion-electron recombinations, positron releases up to 1 keV in the terminal blob region [1]. After all this energy converts into heat. This local heating effect makes the medium to heat up and melt, especially at the region where the bulk temperature of the medium is close (but slightly below) the phase transition temperature. In this case this effect leads to a peculiar temperature dependence of the lifetime of the long-lived LT spectra component. We introduce a model to describe the temperature behaviour of the ortho-positronium lifetime for three simple alcohols (methanol, ethanol and butanol) at the melting range.

cond-mat.other↗

arXiv2002

The Determination of Microscopic Surface Tension of Liquids with a Curved Interphase Boundary by Means of Positron Spectroscopy

The method for determination the microscopic surface tension $σ(R)$ of nanobubbles is developed based on the new elaboration of the positronium bubble model. In contrast to existing structureless Ps bubble models, our version contains experimentally known molecular characteristics of liquids. The relationship, similar to Tolman's equation, between $σ(R)$ and the radius $R$ of the Ps bubble is derived on a microscopic basis. Numerical values for $σ(R)$ are determined for a large number of liquids and liquified gases. The results are in agreement with the theoretical expectations and independent evaluations, available in literature.

physics.chem-ph↗

arXiv2002

Electric field effect on positronium formation in liquids

The comparison of different models (the Ore, spur and blob models) of positronium (Ps) formation is presented. Because in molecular media Ps is formed in the terminal positron blob and not in an ordinary spur, the application of the blob model seems to be the most adequate. We extend this model for consideration of the Ps formation in the presence of external electric field ($<100$ kV/cm). In the simplified limiting case, this approach provides a formula similar to the Onsager one for the geminate recombination probability. The influence of ion-electron recombination and other intrablob processes on Ps formation is taken into account. The role of quasifree positronium in Ps formation process is discussed.

physics.chem-ph↗