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。 关键词：

TEMPERATURE DEPENDENCE OF CONDENSED METHANE STUDIED BY POSITRON LIFETIME MEASUREMENTS

Positron lifetime spectra have been measured as a function of temperature from 30 K to 150 K in condensed methane. In solid phase, the positronium (P_s) formation in free volume and the P_s yield of 27% were observed. The sigmoidal variation of o-P_s lifetime with temperature was interpreted by P_s trapping in the thermally activated defects. The activated energy E_a = 0.10±0.02 eV was derived in terms of P_s trapping model. In liquid methane with saturated vapor pressure, the results that o-P_s lifetime is 5-7ns and P_s formation probability is 36% indicate the P_s bubble formation. The temperature dependence of the bubble size and surface tension were estimated.