Excitation of Molecular Vibrations by Positron Impact

Abstract

Absolute cross sections for the vibrational excitation of CO, CO2, and H2 by positron impact are presented for incident positron energies from 0.5 eV to several electron volts. The measurements use a novel technique that exploits the adiabatic motion of a positron beam in a strong magnetic field. This work is the first systematic experimental study of vibrational excitation by positron impact, and extends to energies where positron measurements have traditionally been difficult. The measured cross sections are compared with available theoretical calculations.

Practical limits on positron accumulation and the creation of electron-positron plasmas

“…As an estimate. we assume cooling on CO 2 which has 8Ecol = 0.3 eV and a collision cross section a -10-16 cm 2 [50]. With these assumptions vco, = n, Ovth -_ 15 x 10 4 p s--1, (14) where n,, is the CO 2 number density and P is the pressure in mTorr.…”

Positron Plasmas in the Laboratory

“…At the end of the grant period, work focused on developing techniques to go to very low values of positron energy, e.g., < 100 meV. [2,5,7,8,11,12,14,[18][19][20][21][22]26] Rotating-wall compression of positron plasmas and polyatomic buffer-gas cooling. In collaboration with R. G. Greaves, First Point Scientific, Inc.…”

Thermally Excited Modes in a Pure Electron Plasma

“…Unneutralized plasmas are unique in that they can be trapped in a rotating near-thermal-equilibrium state by static electric and magnetic fields. Steady-state confinement of N 10 3 -10 9 electrons, ions, or antimatter particles [1,2] is routinely used in plasma experiments, atomic physics [3], and spectroscopy [4]. The thermal equilibrium characteristics become most evident with the formation of Coulomb crystals [5] when pure ion plasmas are cooled to the liquid and solid regimes at sub-Kelvin temperatures, but the higher temperature plasma regime studied here is also well described by near-equilibrium statistical mechanics [6].…”