Study of the interactions between positronium and atoms or molecules

点击翻译按钮获取中文摘要

We have studied (1) spin orbit interaction during positronium scattering, and (2) pickoff annihilation of positronium. The results are as follows.(1) Spin-orbit interaction of positronium with atoms, predicted by Mitroy and Novikov, has been detected experimentally. Newly developed positron lifetime apparatus employing digital processing was used. We have found that the lifetime of the magnetically unperturbed ortho-positronium in Xe gas of 1 atm decreases significantly when a magnetic field of 1.0 T is applied. This decrease is attributed to the Ps spin conversion caused by the spin-orbit interaction during the positronium-Xe collision. The annihilation cross section of ortho-Ps due to this interaction has been determined to be three times as large as that expected by Mitroy and Novikov.(2) Systematic study of the pick-off annihilation of ortho-positronium in 19 gases was performed. The values of the normalized collisional annihilation-rate, ^1Z_<eff>, have been measured to be 0.1-2.31. The ^1Z_<eff> for Xe (1.25) and CH_3I (2.31) are exceptionally large while the values for the other gases are below 0.73. The value for Xe is explained in terms of the spin-orbit interaction. CH_3I is still under investigation. The value for N_2O, which was reported to be anomalously high, has been revealed to be similar to those of the other gases.