Effects of electrical conductivity on the formation and annihilation of positronium in porous materials
Effects of electrical conductivity on the formation and annihilation of positronium in porous materials
复制标题
多孔材料中电导率对正电子素形成和湮灭的影响
DOI：
10.1039/c6cp07483a
复制
发表时间：
2017
影响因子：
3.3
通讯作者：
Zhou Wei
中科院分区：
文献类型：
--
作者：
Li Chongyang;Zhao Bin;Zhou Bo;Qi Ning;Chen Z. Q.;Zhou Wei
在本文中，我们给出了正电子素的形成依赖于多孔材料的导电性的初步证据。以多孔纳米γ-Al_2O_3为基材，通过机械混合的方法在其上填充了不同同素异形体的碳(商品石墨、炭黑、碳纳米管和国产有序介孔碳)。测量了这些复合材料的正电子寿命和湮没辐射的多普勒展宽。在纯γ-Al_2O_3样品中，有两个长寿命的正电子成分τ-3(3.5 ns)和τ-4(101.3 ns)，强度分别为1.0%和24.6%，这分别表明正电子在小孔和大孔中的形成和湮灭。在碳填充的γ-Al_2O_3样品中，随着碳含量的增加，最大寿命τ_4和强度I4都呈现出不断减小的趋势。S参数的多普勒展宽与τ4和I4的变化趋势相似。这表明碳对正电子素有猝灭作用，也抑制了正电子素的形成。在这四种碳同素异形体中，碳纳米管的猝灭和抑制作用最强，而石墨的作用最弱。进一步的研究表明，τ_4和I_4的下降速率以及S参数取决于碳填充γ-Al_2O_3的导电性和填充碳的比表面积。我们的结果表明，正电子的形成和湮灭强烈地受到材料的导电性的影响。
In this paper we show the preliminary evidence that the formation of positronium depends on the electrical conductivity of porous materials. Porous nano γ-Al2O3 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-Al2O3 sample, there are two long positron lifetime components τ3 (3.5 ns) and τ4 (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-Al2O3 samples, the longest lifetime τ4 and its intensity I4 both show a continuous decrease with increasing carbon content. The Doppler broadening S parameter shows a similar tendency to τ4 and I4. 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 τ4 and I4 as well as the S parameter depend on the electrical conductivity of the carbon filled γ-Al2O3 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.