Creation and Annihilation of Microclusters with an Impurity Core Ion in Low-Temperature Condensed Matter

引入超流氦中的杂质离子形成带电的聚集体，称为雪球。在本研究项目中，通过导入高能重离子碰撞中产生的放射性离子，形成了这样的雪球。因此，短寿命的离子，如^<12>B（半衰期20.4 ms）和^8 Li（半衰期842 ms）被用作杂质核心离子。本文采用探测核心离子核中β射线和α粒子的新方法，研究了雪球的产生和湮灭过程。实验研究是沿着两条路线进行的：1）确定了成核几率; 2）通过观测β射线的衰变数，测量了雪球的形成数与撞击超流氦的离子数的比值。3）通过测量β射线的衰变数，计算了雪球的形成数与撞击超流氦的离子数的比值。4）通过测量雪球的形成数，计算出雪球的形成数与撞击超流氦的离子数的比值。5）通过测量雪球的形成数，计算出雪球的形成数与撞击超流氦的离子数的比值。5）通过测量<12>雪球的形成数，计算出雪球的形成数与撞击超流氦的离子数的比值。6）通过测量雪球的形成数，计算出雪球的形成数与撞击超流氦的离子数的比值。7）通过测量雪球的形成数，计算出雪球的形成数与撞击超流氦的离子数的比值。8）通过测量雪球的形成数，计算出杂质核离子的核极化保持性是研究雪球中与杂质离子直接相邻的氦原子相态的一个很好的探索。我们的结果反映了雪球的结构最有可能是固体实体，原子结构是高度对称的，正如人们通常认为的那样，二十面体取向可能是核心离子周围原子构型的候选者之一。

Impurity ions introduced in superfluid helium form charged aggregations called snowballs. They are considered microclusters tightened through electrostriction.In this research project, such snowballs are created through introduction of radioactive ions produced in high-energy heavy-ion collisions. Thus short-lived ions, such as ^<12>B (halflife 20,4 ms) and ^8Li (halflife 842 ms) are used as impurity core ions. The processes of creation and annihilation of snowballs are studied employing novel methods of detecting beta rays and alpha particles from the nuclei of the core ions.The experimental studies were proceeded along two lines, 1) nucleation probability has been determined ; the ratio of number of snowballs formed to number of impinging ions into superfluid helium, has been measured by observing the numbers of decay beta rays from ^<12>B.2) The preservation of nuclear polarization in impurity core ions is a good probe to seek into the phase of helium atoms as directly neighboring the impurity ions in snowballs. Our result reflects that the structure of a snowball is most probably of solid entity and the atomic structure is highly symmetric, as often presumed, the icosahedral orientation may be one of the candidates for the atomic configuration around the core ion.The experimental studies are carried out at RCNP,Osaka University and partly at RIKEN using the cyclotron systems.