Positronium formation in molecular oxygen

16th International Conference on Positron Annihilation

Archer, J.^1 ; Trilov, S.M.^1 ; Coleman, P.G.^1

Department of Physics, University of Bath, Bath BA2 7AY, United Kingdom^1

关键词: Beam intensity;    Dissociative attachment process;    Energy dependence;    Ionization measurements;    Measurements of;    Positron energy;    Positronium formation;    Projectile energy;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/443/1/012001/pdf
DOI  :  10.1088/1742-6596/443/1/012001

来源: IOP

【 摘 要 】

New measurements of the positronium (Ps) formation cross section in molecular oxygen have been made using the 'positron loss' technique used in earlier measurements in the noble gases-the reduction in beam intensity being attributed to Ps formation. The results are generally in agreement, in terms of dependence on incident positron energy, with earlier measurements, but are lower in magnitude than those deduced from total ionization measurements below the first threshold for direct ionization, which employed ion detection. QPsfor molecular oxygen exhibits an interesting peak-like dependence on incident positron energy just above threshold, and possible reasons for this structure are discussed. These include the possibility of a dissociative attachment process; a unique peak at similar projectile energies has long been observed in electron-oxygen scattering. The most likely explanation, however, lies in coupling between Ps formation and excitation to the continuum, the latter having previously been shown also to have a peaked energy dependence above threshold.