VACANCY FORMATION ENERGY IN MOLECULAR SOLID CH4

The Doppler broadening energy spectra have been measured on high-purity condensed CH4 in temperature range from 30K to 105K.In solid phase and below the melting point,the variations of S-parameter with temperature were interpreted as o-Ps trapped in the thermally activated vacancy-type defects.A vacancy formation energy of 0.10±0.02eV was derived by positronium trapping model.

用正电子湮没寿命谱研究凝聚态甲烷的温度关系

在30—150K温度范围内,测量了高纯凝聚态甲烷中的正电子寿命谱随温度的变化。在固态甲烷中,正电子素(简称Ps)在自由体积中形成,形成率为～27%。正-正电子素(其符号为o-Ps)的寿命随温度变化的特征可用o-Ps在热激活空位型缺陷中的捕获来说明,且由Ps捕获模型和实验测得的o-Ps寿命求得缺陷激活能E_a=0.10±0.02eV。在液态甲烷中,Ps形成率高达36%,且o-Ps寿命长达5—7ns,这表明液态甲烷中形成了Ps气泡态。我们用经验公式估算了这种气泡的尺寸及其微观表面张力。