Study of the interactions between positronium and atoms or molecules

我们研究了(1)正电子散射过程中的自旋轨道相互作用，(2)正电子的拾取湮灭。结果如下：(1) Mitroy和Novikov预测的正电子与原子的自旋轨道相互作用已经被实验检测到。采用了新研制的数字处理正电子寿命仪。我们发现，当施加1.0 T的磁场时，在1atm的Xe气体中，无磁扰动的正电子离子的寿命显著降低。这种下降是由于正电子- xe碰撞过程中自旋轨道相互作用引起的Ps自旋转换。由于这种相互作用，正交p的湮灭截面已被确定为Mitroy和Novikov预期的三倍。(2)系统地研究了正电子在19种气体中的拾取湮灭。经测量，归一化碰撞湮灭率^1Z_<eff>的值为0.1-2.31。Xe（1.25）和ch3i（2.31）的^1Z_<eff>特别大，而其他气体的^1Z_<eff>则低于0.73。Xe的值可以用自旋轨道相互作用来解释。CH_3I仍在调查中。据报道，N_2O的值异常高，与其他气体的值相似。

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.