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1
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Revision of the Model of Formation of Radiolytic Products in Aqueous Solutions

100%
Stepanov S., Byakov V.
Acta Physica Polonica A
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2005
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vol. 107
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issue 4
651-660
EN
Mathematical model of formation of radiolytic products (e^-_{aq}, H, OH, H_2, H_3O^+, OH^-, Ps) in water is developed. It takes into account (1) reactions between dissolved scavengers of thermalized and hydrated electrons as well as epithermal ones; (2) ambipolar diffusion expansion of the intratrack species; (3) additional channels of Ps and H_2 formation due to appearance of weakly trapped electrons. Good agreement is obtained with experimental data on kinetics of accumulation of the products in pure water and their concentration variations in aqueous solutions.
2
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Primary Chemical Reactions Induced by Transformation of Radioactive Nuclei in Solids at Low Temperatures. Investigation by Means of the Emission Mössbauer and Positron Spectroscopies

81%
Byakov V., Kulikov L., Perfil'ev Y., Stepanov S.
Acta Physica Polonica A
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2005
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vol. 107
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issue 5
792-798
EN
A set of early chemical reactions in grapes of ionization (blobs) arising in tracks of fast electrons and positrons in liquids as well as formed by the Auger electrons in frozen aqueous media around decaying Mössbauer ^{57}Co or ^{119m}Sn nuclei is suggested. The mechanism predicts a correlated variation of the formation probabilities of intrablob final products, namely Fe^{2+}-Fe^{3+} or Sn^{2+}-Sn^{4+} ions, positronium atom and molecular hydrogen with variation of temperature, degree of crystallinity, concentration of electron scavengers. These correlations indicate on similarity of chemical processes as in blobs created by ^{57}Co and ^{119m}Sn after their decay as well as in blobs produced in tracks of fast positrons and electrons.
3
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Developing New Routine for Processing Two-Dimensional Coincidence Doppler Energy Spectra and Evaluation of Electron Subsystem Properties in Metals

81%
Stepanov P., Stepanov S., Byakov V., Selim F.
Acta Physica Polonica A
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2017
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vol. 132
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issue 5
1628-1633
EN
A digital coincidence Doppler broadening (CDB) spectrometer consisting of two HPGe detectors is assembled; the energy resolution of each detector is 1.1 keV at energies near the annihilation line. Two desktop applications for CDB spectra processing are developed. TLIST Processor converts two-dimensional CDB spectra into one-dimensional spectra. Another tool SW Calculator deconvolutes the experimental CDB spectra into contributions from positron annihilation with valence, core and conduction band electrons. The program estimates the energies of the corresponding electrons and evaluates S and W parameters of the CDB spectra.
4
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Primary Radiolytic Reactions in the Auger Blob Formed by Radioactive Transformation of ^{57}Co into ^{57}Fe in Frozen Aqueous Medium

81%
Stepanov S., Perfil'ev Y., Byakov V., Kulikov L.
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vol. 125
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issue 3
843-845
EN
The emission of the Auger electrons during the formation of the Mössbauer nucleus ^{57}Fe leads not only to the formation of multicharged ^{57}Fe^{n+} ion, but also to the appearance of the Auger blob, a cloud of several hundreds of ion-electron pairs (H_2O^{+}, e¯) in the solvent around the Fe ion. Fast radiation-chemical reactions therein determine the experimentally observable ratio of the yields of final chemically stable charged states of the Mössbauer ions (Fe^{3+} and Fe^{2+}). This ratio strongly depends on reaction rates constants between H_2O^{+}, e¯, and the solute S. We have shown that in contrast to radiation chemical data the reactivity of NO_{3}^{-} anions with quasi-free track electrons in frozen aqueous solutions exceeds those of H_{3}O^{+}, ClO_{4}^{-}, and HSO_{4}^{-} ions only by a factor of three instead of ≈ 100 which follows from the radiation chemical experiments.
5
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Application of Positron Spectroscopy for the Detection of Nanostructures in Water-Alcohol Mixtures

81%
Stepanov P., Byakov V., Zaluzhnyi A.
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vol. 125
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issue 3
767-769
EN
Analysis of the o-Ps lifetimes concentration dependences in water-propanol mixtures (with and without CoCl_2 additive) shows that this mixture looks like an emulsion of alcohol micelles in water at propanol mole fractions 0.1-0.4.
6
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Positrons and Positronium Atoms in a Condensed Phase Close to Its Melting Point

71%
Stepanov S., Zvezhinskiy D., Byakov V., Duplâtre G., Stepanov P.
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vol. 125
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issue 3
691-695
EN
Investigation of the local heating effect at the terminal part of a fast positron track sheds light on the accumulation of defects in a frozen medium close to its melting point. Estimations of the formation energies of the structural defects which may trap the Ps atom as well as a contribution of these defects to the enthalpy of fusion are obtained.
7
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Formation of Quasi-Free and Bubble Positronium States in Water and Aqueous Solutions

71%
Stepanov S., Duplâtre G., Byakov V., Zvezhinskiy D., Subrahmanyam V.
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vol. 125
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issue 3
770-774
EN
It is shown that in aqueous solutions a positronium atom is first formed in the quasi-free state, and, after 50-100 ps, becomes localized in a nanobubble. Analysis of the annihilation spectra of NaNO_3 aqueous solutions shows that the hydrated electron is not involved in the positronium (Ps) formation.
8
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Role of Trapped and Solvated Electrons in Ps Formation

71%
Stepanov S., Byakov V., He C., Hirade T., Mikhin K.
Acta Physica Polonica A
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2005
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vol. 107
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issue 4
642-650
EN
Role of trapped and solvated electrons in Ps formation is discussed. Combination of thermalized positron with such electrons is possible from the viewpoint of the energy balance and may results in Ps formation. This process proceeds during all e^+ lifetime in matter. Fitting of raw experimental e^+ - e^- annihilation spectra has to be based on an adequate physical input, which often leads to necessity of nonexponential deconvolution of the spectra. We have interpreted the Ps formation data in polyethylene, ethylene-methylmethacrylate and polymethylmethacrylate in dark and in light vs. time of the measurement and temperature. Parameters characterized accumulation of trapped electrons and their recombination with counter ions and positrons are obtained.
9
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Track Effects in Positronium Formation

71%
Stepanov S., Byakov V., Duplâtre G., Stepanov P., Bokov A.
Acta Physica Polonica A
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2017
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vol. 132
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issue 5
1461-1465
EN
We discuss some aspects important for interpretation of the Ps formation process in liquids and molecular media: (1) inhomogeneity of intratrack reactions and parameters of the e⁺ track, (2) final states of e⁺, its solvation in polar and nonpolar liquids, relation to e⁺ mobility, (3) quasi-neutrality of the e⁺ blob and its ambipolar outdiffusion, (4) appearance of the "in-blob" and "out-of-the-blob" positron fractions, and (5) electric field effect on Ps formation.
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