Intra-Spur Reactions Studied by Using Positronium Formation

正电子（Ps）是在正电子（e^+）和电子（e^-）之间形成的类氢原子。Ps的形成机制尚不清楚。p的形成有两种模型。矿石模型假设高能（超热）e^+从介质中获得一个电子，而激波模型假设e^+在其自身的末端辐射激波中几乎被热化，并与电离产生的e^-（多余电子）结合。首席研究员长期参与这一问题的研究，并得出结论，至少对于凝聚分子物质中Ps的形成，spur模型是比前者更好的模型。本研究旨在推进这一观点，并有望使“Ps形成实验”成为研究快速内刺反应的研究工具。实验测量了各种惰性和亲电分子混合物中Ps的产率。马刺过程的重要性已得到证实。此外，还发现了Ps形成的一个新方面，即“激发态形成Ps”。通过这个新过程的发现，Ps形成的图景有了很大的改进，我们发表了一篇题为“a new Model of Positronium formation”的论文。关于矿石模型和马刺模型相互相对重要性的评价还存在一些问题。在一篇综述文章中对这些问题进行了总结。

Positronium (Ps) is a hydrogen-like atom which is formed between positron (e^+) and electron (e^-). The mechanism of Ps formation is not yet made clear. There are two models of Ps formation. The Ore model assumes that energetic (epithermal) e^+ picks up an electron from the medium, and the spur model assumes that e^+ is nearly thermalized in its own terminal radiation spur and combines with e^- (excess electron) that is ejected by ionization.The head investigator has long been involved in the research of this problem, and has a conclusion that the spur model is a better model than the former at least regarding Ps formation in condensed molecular substances. The precious study aims to advance this viewpoint and hopefully make the "Ps formation experiment" a research tool to study fast intra-spur reactions.The experiments have been to measure Ps yield in various mixtures inert and electrophilic molecules. The importance of the spur process has been confirmed. Moreover a new aspect of Ps formation, namely "Ps formation from excited molecular states" has been found. By the discovery of this new process, the picture of Ps formation has been improved substantially, and we have published a thesis titles "A New Model of Positronium formation".There still remains problems concerning evaluation of mutual relative importance of the Ore model and the spur model. These problems have been summarized in a review article.