Positronium Annihilation in Oxygen and Nitrogen Mixture

Formed in silica aerogels, positronium annihilation in oxygen and nitrogen mixture is studied by a simple and convenient method. The results show that ortho-positronium （o-Ps） lifetime is significantly shortened when some oxygen is introduced into ni- trogen gas and that the o-Ps collisional quenching rate for an oxy- gen molecule is （28.0±0.4） ±ts%amagat（1 amagat 2.69± 1025 m-3）. It is found that the o-Ps annihilation rate in oxygen of latin at room temperature is （25.5±0.5） us-1 and that the effective num- ber of electrons per oxygen molecule available for 27 annihilation of positron in the o-Ps is （34.6±0.4）.

二氧化硅气凝胶毡在直埋蒸汽管的应用

针对直埋蒸汽管,比较二氧化硅气凝胶毡与传统保温材料的技术经济性能。结合工程实例,对保温层分别为单纯采用耐高温玻璃棉和采用气凝胶毡复合耐高温玻璃棉的直埋蒸汽管的技术经济性进行对比分析。与传统保温材料相比,二氧化硅气凝胶毡有更低的热导率,憎水性能优异,结构稳定,但价格比较高。在直埋蒸汽管道工程中,采用二氧化硅气凝胶毡复合耐高温玻璃棉的保温结构,能降低保温层厚度,减小外护钢管规格,有利于蒸汽管道的长期高效、稳定运行,减少了管道直埋占用空间,有利于城市建设规划。