Large positron annihilation cross sections have been observed for a variety of molecules at various energies below the threshold for positronium formation. These large values are due to vibrational Feshbach resonances VFRs , in which the positron attaches to the molecule while exciting a vibration. This leads to rates of annihilation far greater than those expected for a simple collision. The d...

A comprehensive description of a polarized positron project is presented in terms of physics motivations for utilizing a polarized positron in electron}positron collider experiments, a proof-of-principle experiment and a conceptual design of a polarized positron source for the future linear collider JLC. In order to verify a proposed method of creating highly polarized positron beams via succes...

The electron-positron annihilation source in the Galactic center region has recently been observed with INTEGRAL/SPI, which shows that this 511 keV source is strong and its extension is consistent with the Galactic bulge geometry. The positron production rate, estimated to more than 10 43 per second, is very high and raises a challenging question about the nature of the Galactic positron source...

A second quantised theory of electrons and positrons in a deep time-dependent potential well is discussed. It is shown that positron production from the well is a natural consequence of Dirac’s hole theory when the strength of the well becomes supercritical. A formalism is developed whereby the amplitude for emission of a positron of a given momentum can be calculated. The difference between po...

Ultrarelativistic electron-positron plasmas can be produced in high-intensity laser fields and play a role in various astrophysical situations. Their properties can be calculated using QED at finite temperature. Here we will use perturbative QED at finite temperature for calculating various important properties, such as the equation of state, dispersion relations of collective plasma modes of p...

For the design of the International Linear Collider (ILC) a polarised positron source based on a helical undulator system has been proposed. In order to optimise the positron beam, i.e. to ensure high intensity as well as high degree of polarisation, a measurement of the polarisation close to the positron creation point is envisaged. In this contribution methods to determine the positron polari...

Nanoparticles embedded in a matrix can trap positrons under certain conditions. In such cases nanoparticles can be effectively studied by means of positron annihilation because positron annihilation characteristics contain information related to nanoparticles’ electronic and atomic structure. Of great importance is to calculate the positron response from such nanoparticles. Then, nanoparticles ...

The oblique propagation of arbitrary ion acoustic solitary waves (IASWs) in magnetized electron-positron-ion plasmas is investigated by employing Sagdeev pseudopotential approach. Ions are assumed to be adiabatic having anisotropic thermal pressure. Electrons and positrons considered isothermal, following Maxwellian distribution. In terms electrostatic potential, potential function obtained ana...

A 1500-A Ni(100) film is back illuminated with 5-keV positrons from a brightness-enhanced slow positron beam. Some of the positrons diff'use through the film and are emitted from the front surface by virtue of the Ni having a negative positron affinity. An immersion objective and projector lens form a 1150x image of the reemitted positrons at a 2D position-sensitive detector. With a resolution ...

The prospects of creating positron–electron plasmas confined in a stellarator are discussed. A pure electron plasma would be created before the positrons are introduced, to facilitate efficient injection and a long confinement time of the positrons. Gyrokinetic simulations are presented suggesting that a positron– electron plasma may be stable to low-frequency microturbulence if operated well b...