汞扩散泵——镉捕集阱高真空系统

我们在二级玻璃汞扩散泵的真空系统上使用了室温的镉膜阱,证明镉膜阱能有效地捕集汞蒸气,使被抽容器达到气压力10^-5—10^-7毫米汞数量级的高真空。我们较系统地试验了镉膜的条件对于极限气压的影响,实验结果表明,新蒸发的镉膜效果最好;将镉膜在10^-2毫米汞的气压下搁置10小时后对于极限气压的影响不大;但若将其在大气下搁置10小时,则极限气压约升高一个数量级;进一步延长在大气中的暴露时间(达300天),对极限气压无更大的影响。初步的寿命试验表明,扩散泵工作140小时之后,极限气压才较显著地上升。降低镉膜阱的温度、增加镉膜阱的数目和被抽容器的高温烘烤都是提高真空度的有效途径;在实验中考虑了这些因素,我们曾获得了气压低达10^-9毫米汞数量级的超高真空。

CADMIUM TRAP FOR OBTAINING HIGH VACUUM IN A MERCURY-DIFFUSION PUMPING SYSTEM

We have used a nonrefrigerated cadmium trap in a 2-stage glass mercury diffusion pump vacuum system. Experiments show that the cadmium trap is capable of isolating mercury vapour effectively, as high vacua of 10^-5-10^-7 mmHg is attainable in an evacuated container. Systematic investigations of the effect of the cadmium film under various conditions on the ultimate pressure were carried out. It is found that newly evaporated cadmium films are most effective for that purpose, while after exposure in air of 10^-2 mm Hg, the ultimate pressure does not change appreciably, and that had the cadmium film been exposed to the atmosphere, it would be one order higher than before. Improvement on the ultimate vacuum can be effected by decreasing the cadmium trap temperature and utilizing two or more cadmium traps in series as well as through bake-out of the evacuated container. When such measures are put in force, an ultra-high vacuum of 10^-9 mm Hg is obtained in our test.