S. V. Stepanov

COMMON FEATURES IN THE FORMATION OF PS, MU, RADIOLYTIC HYDROGEN AND SOLVATED ELECTRONS IN AQUEOUS SOLUTIONS

A unified quantitative model of the formation of positronium, muonium and radiolytic hydrogen is proposed. It includes a description of the slowing down and thermalization stages, which are responsible for the initial spatial distribution of primary intratrack species. Possible reactions of “hot” electrons and positrons are discussed. Formation of Ps (Mu) and radiolytic hydrogen is described in terms of diffusion-recombination reactions between thermalized, but yet not solvated positron (muon), radical-cations and track electrons. It is suggested that this intratrack quasi-free electron released from a molecule by the primary ionizing particle is a common precursor of all radiolytic products.

Positronium formation in aqueous solutions of surfactant substances

Abstract Investigating the behaviour of positronium atoms in the solutions of surface actant (SA) substances Jean and Ache [Jean Y.-C. and Ache H. J. (1978) J. Am. Chem. Soc. 100 , 984] have observed a drastic decrease in the intensity I ortho of long-lived ortho-positronium component of Ps atoms when the concentration of SA molecules attains the critical value at which the micelle formation begins. This decrease is up to 1/3 from initial I ortho value and takes place irrespectively to the sign of electric charge of arising micelles. The aim of this communication is to give a physical interpretation and quantitative description of the discussed effect based on the model of Ps formation in liquids by combination of positron with one of the quasifree but yet nonsolvated electrons knocked out by positron during its slowing down process. It is shown that the decrease of I ortho and positronium formation probability P Ps is a result of the space segregation of quasifree electrons (e - ) and positron at the end part of its track containing micelles. According to the sign of its electric charge the micelles are able to accept electrons or positron, making their interaction weaker and thus preventing the Ps formation. The calculations show that the decrease of P Ps (and I ortho ) may be about several tens of per cent in accordance with available experimental data.

Antihydrogen Physics: gravitation and spectroscopy in AEgIS

AEgIS (Antimatter experiment: gravity, interferometry, spectroscopy) is an experiment approved by CERN with the goal of studying antihydrogen physics. In AEgIS, antihydrogen will be produced by charge exchange reactions of cold antiprotons with positronium atoms excited in a Rydberg state (n > 20). In the first phase of the experiment, controlled acceleration by an electric field gradient (Stark effect) and subsequent measurement of free fall in a Moire deflectometer will allow a test of the weak equivalence principle. In a second phase, the antihydrogen will be slowed, confined, and laser-cooled to perform CPT studies and detailed spectroscopy. In the present work, after a general description of the experiment, the present status of advancement will be reviewed, with special attention to the production and excitation of positronium atoms.

Premelting as studied by positron annihilation and emission Mössbauer spectroscopies

We have estimated a local heating which takes place owing to the ionization energy losses at the terminal part of a fast positron track and at nano-vicinities of the 57Fe Mossbauer nuclei in case of the emission Mossbauer spectroscopy. It is shown that in experiments close to the melting point one may expect local melting near the probe species.

Resemblance of Intratrack Processes as a Common Starting Point of Radiation Chemistry and Positron, Muon, and Mössbauer Spectroscopies

A comparison of the yields of final products (57Fe2+, 119Sn2+) of the transformation of Mössbauer nuclei (57Co, 119Sn) in frozen aqueous and alcoholic glassy solutions with the Ps, Ms, and radiolytic-hydrogen formation probabilities in the same liquid media subjected to irradiation with positrons, muons, and fast electrons, respectively shows that the yields of 57Fe2+, 119Sn2+, Ps, Mu, and H2 vary in similar manners with a change in the concentration of electron scavengers or the temperature of the medium. These correlations are a manifestation of a profound similarity between the primary processes occurring in ionizing-particle tracks. Obviously, the recombination of ion-electron pairs inside large swarms (blobs) involving H2O+, e+, μ+, Fe3+, and 119Sn3+, respectively, is the most important process for understanding the formation of H2, Ps, Mu, 57Fe2+, and 119Sn2+.

Microheterogeneity in Mixtures of Benzene with Alcohols and Hydrocarbons: Positron Annihilation and Molecular Light Scattering

Experimentally measured concentration dependences of the probability of positronium formation and the intensity of molecular light scattering in binary benzene-ethanol and benzene-cyclohexane mixtures were analyzed. The observed behavior was explained by association of molecules. Arguments are presented in favor of the formation in benzene-ethanol mixtures of alcohol associates capable of capturing and solvating quasi-free electrons formed in the tracks of high-energy positrons during their passage through the mixture. As the concentration of associates rises, the positronium formation rate decreases while the intensity of the light scattered by them increases. The mean size and lifetime of the associates were evaluated. It was established that, in benzene-ethanol and benzene-cyclohexane mixtures at temperatures below room temperature, benzene associates are formed.

What do Positrons Say about the Structure and Properties of Fluids

Applications of positron annihilation spectroscopy to fluid state physics and chemistry are discussed. Special attention is paid to problems of surface (interface) layer structure, molecular orientations in the layer, and the effects of free‐surface curvature and age on surface tension. Positron investigations of the structure of liquid mixtures, including microheterogeneity studies, are considered.

Role of ionizing radiation in the natural history of the Earth

Abstract A role of ionizing radiation in some global processes and events in geological history of the Earth is considered. In particular, we discuss: (1) the influence of ionizing radiation from radioactive nuclei disseminated in sedimentary rocks on the transformation of terrestrial organic matter into stone coals and oil; (2) the effect of cosmic rays from Supernova stars as a common cause of quasi-regular global geological processes and biocatastrophes.

Primary Chemical Reactions Induced by Radioactive Nuclear Transformations

A series of chemical reactions is suggested to describe primary chemical transformations induced by Auger electrons from radioactive nuclear decay in glassy and crystalline frozen aqueous media. The mechanism is based on Mössbauer emission spectroscopy data supplemented by data on reactions in the tracks of fast positrons and electrons in an aqueous medium. It is shown that variation of temperature, the degree of crystallinity, the concentration of electron acceptors, etc., results in correlated changes in the yields of the final reaction products—Fe2+, Fe3+ or Sn2+, Sn4+ ions, positronium atoms, and molecular radiolytic hydrogen. These correlations indicate the similarity of chemical processes in the nanometer vicinity of decayed 57Co and 119mSn nuclei and in the tracks of fast positrons and electrons. This similarity is caused by the same behavior of secondary intratrack electrons produced due to ionization losses of fast positrons, electrons, and Auger electrons.

A Mössbauer Tin-119 Emission Spectroscopy Study on Electron Scavenging in Frozen Solutions

The effects of impurity ions on the yield of valence states of tin after the internal conversion isomeric transition of 119mSn in frozen alcohol solutions was studied. The ratios of rate constants for electron scavenging by the solutes H+, Cr+2, and Cu+2 were determined. Mössbauer emission spectra showed that, as the solute concentration increased, the yield of Sn+4 increased. The calculation of the electron scavenging rate constants in terms of various models (simple competitive reactions, the kinetics involving the epithermal electron, and the electron diffusion model) showed that metal ions have a higher electron scavenging ability. It was concluded that the presolvated electron takes part in reactions with the solutes.