Vapour pressure of isotopic liquids

In order to extend previous studies of vapour pressure of isotopic liquids in a wider temperature range, a new cryostat was built. The single stage separation factor α of the isotopic pairs36A10A and20Ne–22Ne was measured up to a vapour pressure of 12 atmospheres, using natural isotopic mixtures. The logarithm of the vapour pressure ratio of the pure isotopes was derived from α and found to be linearly dependent on 1/T within the experimental error, which amounts to less than 2‰ at boiling temperature of neon. The dependence on 1/T is given numerically by ln (p36/p40)=1.31(1/T) 8.95·10−3 for argon, from 83°K to 120°K, and by ln (p20/p22)=2.510(1/T) 5.673·10−2 for neon, from 25°K to 40°K. A brief discussion of the results is given.