ISOTOPE SIEVE FOR 4HE VS 3HE . LOW-TEMPERATURE HEAT CAPACITY OF SIO2 GLASS BEFORE AND AFTER CONTACT WITH 4HE AND 3HE

The heat capacity of two samples of annealed SiO2 glass has been measured over the range 0.5°â4.2°K. The data for a solid cast cylinder are represented by C = 0.33T + 0.271T3 + 0.0220T5μgibbs / g. A hollow cylinder made from tubing gave the result C = 0.26T + 0.234T3 + 0.0165T5μgibbs / g. The heat capacity of each sample was also measured at 90 kG with no detectable change. It has been found that 4He can be sorbed by the glass at temperatures below 4.2°K and cannot be appreciably removed by long evacuation at 4.2°K. This effect has been studied in terms of the temporarily altered heat capacity after the glass has been exposed to liquid and gaseous 4He. Similar experiments with 3He indicate that it is not sorbed in SiO2 glass below 4.2°K, and exposure to liquid or gaseous 3He produces no change in heat capacity. It is suggested that SiO2 glass may be useful in separating 3He and 4He by selective sorption. © 1969, American Institute of Physics. All rights reserved.