Positronium Study of Structural Nanovoids in Model Glasses

高放射性核废料通过与玻璃混合而固定，可以安全地储存1000多年。这些放射性核素被限制在放射性废物玻璃（RWG）的本征结构纳米空隙中，通常是SiO_2-B_2O_3基玻璃。因此，研究放射性核素原子（离子）占据纳米空隙并在辐照环境下长期储存的稳定性是非常重要的。采用Tao-Eldrup-Nakanishi-Wang-Jean模型和零点气泡模型，分别从正电子湮没的二维角关联（2D-ACAR）动量分布和正电子湮没的拾取湮没时间（hSetime）两个方面，研究了纳米空穴中正电子偶素（Ps）的平均半径。两个实验的平均半径彼此吻合良好，除了在含Fe杂质的玻璃中固定了比拾取寿命稍小的半径。纳米孔洞的平均半径随着掺杂氧化物（Li、Na和K）的摩尔分数的增加而迅速减小，这是因为氧化物中的阳离子按孔洞尺寸的顺序占据纳米孔洞，半径随掺杂氧化物的摩尔分数呈缓慢的线性变化。网络较松散的氧化物（B_2O_3，Al_2O_3），表明网络较牢固的氧化物掺入到玻璃结构中。网络但不在纳米空隙内。这些发现为研究RWG在长期储存过程中的稳定性提供了一个很有前途的工具。

High-level radioactive nuclear waste is are immobilised by mixing it with glass to be stored safely for a long time more than 1000 years. These radioactive nuclides are confined in the intrinsic structural nanovoids of the radioactive waste glasses (RWG), usually SiO_2-B2O_3 based glasses. Thus it is very important to study haw the nanovoids are occupied by the radioactive nuclide atoms (ions) and stable under the irradiation environment during the long-term storage.Many kinds of SiO_2 based model glasses were prepared. We employed two independent experimental methods of positronium (Ps) formed in the nanovoids to obtain average radius of the nanovoids, the average radii are obtained from pick off annihilation hSetime of Ps using Tao-Eldrup-Nakanishi-Wang-Jean model and from two-dimensional angular correlation of positron annihilation (2D-ACAR) momentum distribution using a zero-point bubbles model.In SiO_2 based model glasses, the average radii from the two experiments agree well with each other except fix slightly smaller radii from the pick-off lifetimes in the glasses containing Fe impurities. The average radius of the nanovoids decreases rapidly with increasing the mole fraction of the doped oxides which belong to the network modifiers (Li, Na and K)because the cation of the oxides occupy nanovoids in the order of the size of them The radius show sluggish and linear change with the fraction. Of the network loaner oxides (B_2O_3, Al_2O_3), which exhibits that the network firmer oxides are incorporated at the glass structural. Networks but not within nanovoids. These findings give us useful into oration on the structural nanovoids and suggest a promising tool for the study of the stability of the RWG during the long-term storage.