The field of experimental positronium physics has advanced significantly in the last few decades, with new areas of research driven by the development of techniques for trapping and manipulating positrons using Surko-type buffer gas traps. Large numbers of positrons (typically ≥106) accumulated in such a device may be ejected all at once, so as to generate an intense pulse. Standard bunching techniques can produce pulses with ns (mm) temporal (spatial) beam profiles. These pulses can be converted into a dilute Ps gas in vacuum with densities on the order of 107 cm−3 which can be probed by standard ns pulsed laser systems. This allows for the efficient production of excited Ps states, including long-lived Rydberg states, which in turn facilitates numerous experimental programs, such as precision optical and microwave spectroscopy of Ps, the application of Stark deceleration methods to guide, decelerate and focus Rydberg Ps beams, and studies of the interactions of such beams with other atomic and molecular species. These methods are also applicable to antihydrogen production and spectroscopic studies of energy levels and resonances in positronium ions and molecules. A summary of recent progress in this area will be given, with the objective of providing an overview of the field as it currently exists, and a brief discussion of some future directions.

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Experimental progress in positronium laser physics

Positronium formation reaction of trapped electrons and free positrons: delayed formation studied by AMOC

Positron diffusion in solids and in liquid metals

A model function for the lifetime analysis of slowly thermalising ortho-positronium is presented. Simulated spectra are analysed for a wide range of parameters and of statistical contents. A comparison with standard two-component analysis shows the power of the new model for specific problems. Experimental support in alumina fine particles is presented.

The analysis of non-exponential decay in relation to positronium thermalization

Positron annihilation spectroscopy with its special methods of positron annihilation lifetime spectroscopy (PALS), Doppler-broadening of annihilation radiation, and angular correlation of annihilation radiation represents an important experimental tool for the study of the free volumes in amorphous and semicrystalline polymers. From PALS, the most important technique for the investigation of polymers and other molecular materials, the size distribution of subnanometer-size local free volumes (holes) can be determined. The fundamentals and experimental techniques of this method for the investigation of bulk and near-surface properties are outlined. Typical examples for the study of the temperature and pressure dependence of the free volume and the effect of chemical heterogeneities on PALS are presented.


Keywords:

free volume;
glass transition;
thermal properties;
structure-property relations;
nanoheterogeneity

Andreas Siegle

Papers

Annihilation of incompletely thermalized positronium studied by age-momentum correlation