A SEARCH FOR HE-4 IN C-60 INTERSTITIAL SITES

We present low temperature adsorption isotherms for He-4 on C-60 films . Data is obtained by monitoring the frequency of C-60 coated quartz c rystal microbalances versus pressure as He-4 gas is added to an experi mental cell at constant temperature. Data for two thicknesses of C-60 (1790 Angstrom and 3200 Angstrom) taken in the range 1.5 K < T < 1.7 K yield an upper limit for intercalation of He-4 into the C-60 intersti tial sites of 0.05 He-4 atoms per C-60 molecule in general agreement w ith earlier work.