Spin-Orbit Quenching of Positronium during Atomic Collisions

Abstract

When positrons are injected into a gas, 75% of the positronium (Ps) is likely to be formed as longlived ortho-Ps. The main decay mechanisms for the ortho-Ps have been assumed to be natural decay of ortho-Ps and pickoff annihilation of the positron during Ps-atom collisions. A third possibility for annihilation is ortho-Ps ! para-Ps conversion due to the spin-orbit interaction between the atom and colliding Ps. This extra quenching mechanism may explain a number of phenomena observed in the annihilation spectrum of Kr and Xe, including the very small Ps fraction of 3% seen for Xe.

Polarizabilities and tune-out wavelengths of the hyperfine ground states ofRb87,85

“…The differences of the present RCICP calculations and other available results [20,22,34,36,37] are not more than 0.6%. The dynamic dipole polarizabilities computed with the usual oscillator strength sum-rules can be written as…”

“…The DFCP method is the same as the present RCICP method except that DFCP uses the Bspline basis. The RCICP dipole polarizability is larger than that calculated by the nonrelativistic configuration interaction plus core polarization(CICP) [34], RCCSD of Lim et al [35], and the RMBPT all-order method [39], but smaller than the RCCSD result of Kaur et al [36,37], the earlier MBPT-SD result [38], and the experimental values [40,41]. If the experimental electric dipole matrix elements of the 5s − 5p J transitions [9] are used in the calculation of polarizabilities, the static dipole polarizability of the 5s state is 318.743 a.u., which agrees with the experimental result [41] very well.…”

“…So far none of theoretical results are within the latest experimental error bar, but the RMBPT all-order result is the closest to this latest experimental ratio. [33] 317.62 6.4810 2.3783 CICP [34] 315.7 6.480 2.378 RCCSD [35] 316.17 RCCSD [36,37] 318.47/318.3(6) 6.491(18) MBPT-SD [38] 317.39 RMBPT all-order [22,39] 316.4/322(4) 6.525(37) 2.374 (16) RMBPT [20] 6.520(80) 2.37 Expt.E×H [40] 319(6.1) Expt. [41] 318.79(1.42) Expt.…”

Progress, Challenges and Perspectives in Positron Physics: Report on the XIIth International Positron Workshop

“…They reported a cross section of 3 Â 10 À19 cm 2 ; which is about 100 times greater than that expected from pick-off. In related work, Mitroy and Novikov [30] recently considered the possible role of the spin-orbit interaction in converting ortho-Ps into para-Ps in quasi-elastic collisions. This latter process requires a p-wave collision.…”

“…With regard to a closer coupling between the two collision-physics communities, the next positron workshop will be held in conjunction with the next electron-molecule workshop. In particular, the XIIIth International Workshop on Positron and Positronium Physics and the International Symposium on Electron-Molecule Collisions and Swarms will be held in Campos de Jorda˜o, in State of Sa˜o Paulo, Brazil, July [27][28][29][30]2005. This is an exceedingly welcome development that is likely to foster closer ties between these communities, and it has the potential to spawn a number of new synergetic activities.…”