Positron Annihilation in Solids
Positron Annihilation in Solids
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固体中的正电子湮灭
DOI：
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发表时间：
1970
期刊：
影响因子：
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通讯作者：
R. M. Singru
中科院分区：
文献类型：
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作者：
R. M. Singru
正电子是电子的反粒子，“狄拉克的电子相对论”预言了它的存在。“安德森”在宇宙射线的云室照片中通过实验发现了正电子。在物质介质中，正电子的寿命并不长，因为它们要么可以与介质中的电子湮灭，要么可以形成寿命较短的正电子原子亚稳定系统。在第一种衰变类型中，称为瞬发或自由湮灭，正电子在热化后，通过单重态碰撞（反平行旋转）或通过三重态碰撞（平行旋转）与介质中的电子湮灭。控制湮灭的选择规则表明，单重态碰撞会导致两个光子沿完全相反的方向发射，每个光子的能量约为 511 (= m0 c2）KeV。这种湮灭的持续时间约为 10-10 秒。另一方面，三重态碰撞会湮灭成三个光子，其寿命约为 10-7 秒。在这种情况下，电子-正电子对的总静止能量 (= 2 m0 c2) 由在一个平面中发射的三个光子共享。单线态（2 个光子）与三线态（3 个光子）湮灭的比率 Ore 和 Powell2 计算得出的利率为“
$${lambda_s}/{lambda_t} = 1115$$
(1)
Positron is the antipartie le of electron and its existence was predicted “by Dirac’s relativistic theory of electron. Positrons were experimentally discovered “by Anderson in cloud chamber photographs of cosmic rays. In a material medium, positrons do not live long because they can either annihilate with electrons in the medium, or can form a metastahle system of a positronium atom which is short-lived. In the first type of decay, called prompt or free annihilation, a positron, after thermalisation, annihilates with an electron in “the medium either througji a singlet collision (spins antiparallel) or through a triplet collision (spins parallel). Selection rules governing the annihilation show that a singlet collision results in emission of two photons in exactly opposite direction and each one having an energv of about 511 (= m0 c2) KeV. This annihilation has a life time ~10-10 s. On the other hand, a triplet collision gives rise to an annihilation into three photons with a lifetime ~10-7 secs. In this case the total rest energy (= 2 m0 c2) of the electron-positron pair is shared between the three photons which are emitted in one plane. The ratio of singlet (2 photon) to triplet (3-photon) annihilation rates was calculated by Ore and Powell2 to “be
$${lambda _s}/{lambda _t} = 1115$$
(1)