Li Chongyang, Zhao Bin, Zhou Bo, Qi Ning, Chen Zhiquan, Zhou Wei
Hubei Nuclear Solid Physics Key Laboratory, Department of Physics, Wuhan University, Wuhan 430072, China.
Faculty of Materials Science and Chemistry, China University of Geosciences, Wuhan 430074, China.
Phys Chem Chem Phys. 2017 Mar 15;19(11):7659-7667. doi: 10.1039/c6cp07483a.
In this paper we show the preliminary evidence that the formation of positronium depends on the electrical conductivity of porous materials. Porous nano γ-AlO was chosen as the base material, and it was filled with carbon of different allotropes (commercial graphite, carbon black, carbon nanotubes and home-made ordered mesoporous carbon) by a mechanical mixing method. The positron lifetime and Doppler broadening of the annihilation radiation were measured for these composites. In the pure γ-AlO sample, there are two long positron lifetime components τ (3.5 ns) and τ (101.3 ns) with intensities of 1.0% and 24.6%, which indicates the formation and annihilation of positronium in small and large pores, respectively. In the carbon filled γ-AlO samples, the longest lifetime τ and its intensity I both show a continuous decrease with increasing carbon content. The Doppler broadening S parameter shows a similar tendency to τ and I. This suggests that carbon has a quenching effect on positronium and also inhibits the formation of positronium. Among these four carbon allotropes, carbon nanotubes have the strongest quenching and inhibition effect, while graphite has the weakest effect. A detailed study further reveals that the decreasing rate of τ and I as well as the S parameter depend on the electrical conductivity of the carbon filled γ-AlO and also the specific surface area of the filled carbon. Our results suggest that the formation and annihilation of positronium are strongly affected by the electrical conductivity of the materials.
在本文中，我们展示了正电子素的形成取决于多孔材料电导率的初步证据。选择多孔纳米γ - AlO作为基础材料，并通过机械混合方法用不同的碳同素异形体（商业石墨、炭黑、碳纳米管和自制的有序介孔碳）对其进行填充。对这些复合材料测量了正电子寿命和湮灭辐射的多普勒展宽。在纯γ - AlO样品中，有两个长正电子寿命成分τ（3.5纳秒）和τ（101.3纳秒），强度分别为1.0%和24.6%，这分别表明了正电子素在小孔和大孔中的形成与湮灭。在填充碳的γ - AlO样品中，最长寿命τ及其强度I都随着碳含量的增加而持续下降。多普勒展宽S参数呈现出与τ和I相似的趋势。这表明碳对正电子素有猝灭作用，并且还抑制正电子素的形成。在这四种碳同素异形体中，碳纳米管具有最强的猝灭和抑制作用，而石墨的作用最弱。详细研究进一步表明，τ和I以及S参数的下降速率取决于填充碳的γ - AlO的电导率以及填充碳的比表面积。我们的结果表明，正电子素的形成和湮灭受到材料电导率的强烈影响。
