高能氩离子辐照SiO_2玻璃的正电子寿命谱学研究

Positron lifetime study of SiO_2 glass irradiated with high energy Ar ions

用 1.15GeV的氩离子在室温下对二氧化硅玻璃样品进行了辐照 ,并通过正电子寿命测量技术研究了辐照后材料微观结构的变化。结果表明 ,在未辐照二氧化硅玻璃中有近 81%的正电子是以正电子素的形式湮灭的 ;根据o -Ps的撞击湮灭寿命确定出未辐照样品的自由体积分布在0 .0 2— 0 .13nm3的区域里 ,平均自由体积半径约为 2 .5nm。辐照后材料的自由体积分布函数变窄 ,峰位下移 ,显示样品经辐照后有密度增大的现象。随着剂量的增大 ,第二正电子寿命成分的强度逐渐增加 ,而相应于o -Ps的寿命成分的强度逐渐减小 ,这被认为是由于辐照产生的电离电子在自由体积中漫游 ,使正电子与这些漫游电子发生湮灭的几率增大 ,从而减小了正电子素的形成几率。

SiO 2 glass specimens were irradiated with 1.15GeV Ar ions at room temperature. Positron lifetime spectroscopy was applied to investigate the radiation induced microscopic changes. It was found that for the unirradiated specimen about 81% positrons annihilate from positronium (Ps) states. Free volumes of about 2.5nm in radius and distributed from 0.02—0.13nm 3 are found from the o-Ps lifetime. Under irradiation the free volume distribution function narrows down and the peak position shifts to lower value, which indicate the densification of the material. With increasing dose, the intensity of the second lifetime component increases whereas the intensity of the component corresponding to o-Ps decreases. This was attributed to the prefered annihilation of positrons with the radiation-ionized electrons wandering in free volumes.