Positron annihilation radiation from the Galaxy has been observed by the OSSE, SMM and TGRS instruments. Improved spectral modeling of OSSE observations has allowed studies of the distribution of both positron annihilation radiation components, the narrow line emission at 511 keV and the positronium continuum emission. The results derived for each individual annihilation component are then comp...

Positron annihilation on a wide variety of atoms and molecules is studied. Room-temperature positrons confined in a Penning trap are allowed to interact with molecules in the form of low-pressure gases so that the interaction is restricted to binary encounters between a positron and a molecule. Data are presented for the g-ray spectra resulting from positrons annihilating in such interactions. ...

BACKGROUND Hydrogel and silicone-hydrogel polymeric materials are widely used in ophthalmology for the manufacture of contact lenses. An important aspect is the investigation of the structure of these materials. OBJECTIVES This study has been conducted in order to compare the degree of disorder and presence of free volumes in the internal structure of the polymeric soft contact lenses Omafilc...

In this work we study electronic properties of quantum dots relevant to Compton scattering and positron annihilation. The system is modeled by an electron gas confined by a spherical potential of given radius and depth. Electron-electron correlations are not considered in this study. We find that the broadening of the electronic momentum density around a suitably defined Fermi momentum scales w...

The structure and defects of nanodiamonds influence the hydrogen sorption capacity. Positronium can be used as a sensor for detecting places with the most efficient capture of hydrogen atoms. Hydrogenation of carbon materials was performed from gas atmosphere. The concentration of hydrogen absorbed by the sample depends on the temperature and pressure. The concentration 1.2 wt % is achieved at ...

When an intense sub-nanosecond positron pulse impinges upon a target, a pulse of g-rays is created which can yield information concerning electron–positron pairs just prior to annihilation. Many conventional g-ray detectors are unable to exploit the timing information contained within such pulses, and we describe here the development of a fast detector that is able to do so. Using a singlecryst...

Techniques to accumulate and cool positrons in Penning traps provide new tools to study atomic and molecular physics and chemistry. This chapter presents an overview of studies of the interaction of low-energy positrons with atoms and molecules using these methods. In the vacuum environment of a trap, isolated twobody interactions of positrons with atoms and molecules can be studied with precis...

We study electron-positron in-flight annihilation as a potential source of quasi-monoenergetic photon (or gamma-ray) beams. A high-intensity tunable-energy (1.515 MeV) gamma source has many potential uses in medical, industrial and security applications. Several electron-positron collision geometries are considered: a) head-on; b) collinear; and c) positron beam incident on a fixed electron tar...