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The interaction of positronium (Ps) with molecular oxygen dissolved in liquids is experimentally investigated. Computer software has been developed for fitting the positron annihilation lifetime spectra in liquids using parameters with clear physical meaning: rate constants of the Ps chemical reactions, annihilation rate constants of the different positron states, probability of Ps formation in a quasi-free state, typical formation time of a Ps nanobubble. Such processing of the spectra allowed identification of the dominant interaction of the Ps atom with dissolved oxygen. It turns out to be mainly ortho–para-conversion (Ps → 1/4 p-Ps + 3/4 o-Ps), but not oxidation (Ps + O2 → e+ + O2−). Values of the reaction rate constants are obtained. [ABSTRACT FROM AUTHOR]

It is shown that during the stopping and decaying of positively charged muon (μ+) in a nuclear emulsion, there arises with a probability of about 10−2 electron with energies between 10 and 180 keV. The energy spectrum and angular distribution of these electrons are measured. A hypothesis on the possible mechanism behind the appearance of electrons corresponding to μ+ decay is put forth. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 onedimensional 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. [ABSTRACT FROM AUTHOR]

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 NaNO3 aqueous solutions shows that the hydrated electron is not involved in the positronium (Ps) formation. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 Moiré 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. AEgIS (Expérience sur l'Antimatière: Gravité, Interférométrie, Spectrométrie) est une expérience approuvée par le CERN qui vise une étude globale de la physique de l'anti-hydrogène. Dans AEgIS, l'anti-hydrogène sera produit par des réactions d'échange de charges d'anti-protons froids avec des atomes de positronium excités dans un état de Rydberg (n > 20). Dans la première phase de l'expérience, l'accélération est contrôlée par un gradient de champ électrique (effet Stark); une mesure subséquente en chute libre dans un déflectomètre de Moiré nous fournira un test du principe d'équivalence faible. Dans une deuxième phase, l'anti-hydrogène sera ralenti, confiné et refroidi par laser pour des études de CPT et de spectroscopie de précision. Après une description générale de l'expérience, nous passons ici en revue l'état d'avancement des travaux en accordant une attention particulière à la production et l'excitation des atomes de positronium. [ABSTRACT FROM AUTHOR]

The article discusses the effects of gas pressure towards the mechanism of propagation in spinning waves during filtration combustion. In a study concerning the surface modes of filtration combustion, it reveals that under certain conditions, the ring front breaks up to form a high-temperature zone on the sample surface. The numerical analysis indicates that spinning waves in filtration combustion has differed significantly from spinning waves in gasless combustion.

Analysis of the o-Ps lifetimes concentration dependences in water-propanol mixtures (with and without CoCl2 additive) shows that this mixture looks like an emulsion of alcohol micelles in water at propanol mole fractions 0.1-0.4. [ABSTRACT FROM AUTHOR]

The emission of the Auger electrons during the formation of the Mössbauer nucleus 57Fe leads not only to the formation of multicharged 57Fen+ ion, but also to the appearance of the Auger blob, a cloud of several hundreds of ion-electron pairs (H2O+, 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 (Fe3+ and Fe2+). This ratio strongly depends on reaction rates constants between H2O+, 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 H3O+, ClO- 4 , and HSO- 4 ions only by a factor of three instead of ≈ 100 which follows from the radiation chemical experiments. [ABSTRACT FROM AUTHOR]