Isotope Sieve for 4He vs 3He. The 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°−4.2°K. The data for a solid cast cylinder are represented by ${\text{C\hspace{0.17em}=\hspace{0.17em}0.33T\hspace{0.17em}+\hspace{0.17em}0.271T}}^3{\text{\hspace{0.17em}+\hspace{0.17em}0.0220T}}^5\mathrm{\mu gibbs}\mathrm{\hspace{0.17em}/\hspace{0.17em}}\mathrm{g}$ . A hollow cylinder made from tubing gave the result ${\text{C\hspace{0.17em}=\hspace{0.17em}0.26T\hspace{0.17em}+\hspace{0.17em}0.234T}}^3{\text{\hspace{0.17em}+\hspace{0.17em}0.0165T}}^5\mathrm{\mu gibbs}\mathrm{\hspace{0.17em}/\hspace{0.17em}}\mathrm{g}$ . 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.