A Study on Void Nucleation Mechanisms with Realtime Detection of Nanovoids by Positron Beam

利用慢正电子装置和高能离子加速器相结合的辐照系统，研究了离子辐照过程中产生的空位缺陷。对两种面心立方金属Ni和Al，在辐照和未辐照过程中进行了正电子湮没多普勒展宽的原位测量。我们发现，在S参数的增加发生在辐照过程中的Ni，但不为Al。Ni的结果强烈表明，在辐照过程中的空位浓度是高的相比，辐照后存活，即。例如，其中包括暂时性或无法维持的空缺。这种瞬态空位的形成与缺陷积累或缺陷聚集的过程密切相关。目前的原位观察技术被证明是一个强大的工具，在离子辐照环境下产生的材料中的空位调查。已知正电子湮没辐射的多普勒展宽线形提供比较信息，但关于缺陷特性（诸如密度和开放体积尺寸）的信息较少。相反，正电子寿命测量允许获得定量信息。我们计划做进一步的实验，在原位正电子寿命测量在离子辐照的材料，以获得更准确的洞察辐照效应的动力学，特别是在辐照过程中瞬态诱导的空位特性的定量理解。

Vacancy defects produced during ion irradiation were studied by using an irradiation system combined with a slow-positron apparatus and a high-energy ion accelerator. For two fcc metals of Ni and Al, in situ positron annihilation Doppler broadening measurements were performed during irradiation and non-irradiation. We found that an increase in the S parameter occurs during irradiation for Ni, but not for Al. The result for Ni strongly suggests that vacancy concentration during irradiation is high compared to that survived after irradiation, i. e., it includes transient or non-survivable vacancies. The formation of such a transient vacancy will be closely related to processes of defect accumulation or defect clustering. The present in situ observation technique is demonstrated to serve as a powerful tool for the investigation of vacancies produced in materials under an ion irradiation environment. The Doppler broadening line-shape of positron annihilation radiation is known to provide comparative information but less information about defect characteristics such as the density and the open volume size. In contrast, positron lifetime measurements allow obtaining quantitative information. We plan to do further experiments on in situ positron lifetime measurement during ion irradiation of materials in order to obtain more accurate insights into the dynamics of irradiation effects, in particular a quantitative understanding of vacancy characteristics induced transiently during irradiation.