It is difficult to measure low-energy cross sections for collisions of charged particles with strongly dipolar systems since the magnitude of such cross sections is completely dominated by collisions in the forward direction. Theoretically, it is possible to account for the strong forward scattering using the Born approximation but the procedure for combining Born ‘top-up’ with the more sophist...

Different computational methods are employed to evaluate elastic (rotationally summed) integral and differential cross sections for low energy (below about 10 eV) positron scattering off gas-phase C2H2molecules. The computations are carried out at the static and static-pluspolarization levels for describing the interaction forces and the correlation–polarization contributions are found to be an...

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...

A new monoenergetic MeV positron beam source was designed and constructed at the Lawrence Livermore National Laboratory (LLNL) positron facility. The positron source provides a low emittance beam with high energy resolution for channeling, scattering, and in̄ight annihilation experiments. New beam optics for extracting slow positrons from a moderator mounted in a Pelletron electrostatic accelera...

Compton scattering of gamma rays propagating in a pair plasma can drive the formation relativistic electron positron beam. This process is scrutinized theoretically and numerically via particle-in-cell simulations. In addition, we determine which conditions beam prompt beam-plasma instability convert its kinetic energy into magnetic energy. We argue that such be met at photosphere radius bright...

This paper is devoted to study many-body effects in the positron annihilation experiment, both electron−positron (e–p) and electron–electron (e–e) correlations. Various theories of the e–p interaction in real solids were used to verify them by comparing theoretical and experimental e–p momentum densities in Cu and Y. We show that the lattice potential has an essential influence on the e–p corre...

Absolute measurements are presented for the positron-impact cross sections for direct ionization and positronium formation of noble gas atoms in the range of energies from threshold to 90 eV. The experiment uses a cold, trap-based positron beam and the technique of studying positron scattering in a strong magnetic field. The current data show generally good, quantitative agreement with previous...

The many-body-theory approach to positronium-atom interactions developed in [Phys. Rev. Lett. \textbf{120}, 183402 (2018)] is applied the sequence of noble-gas atoms He-Xe. Dyson equation solved separately for an electron and positron moving field atom, with entire system enclosed a hard-wall spherical cavity. two-particle give energies wave functions Ps eigenstates From these, we determine sca...