Adsorption of helium gas near T(lambda) at low pressures

Cryosorption of helium isotopes (He-4 and He-3) on thin argon cryolayers is studied experimentally in the temperature range 4.2-2 K at low pressures. It is shown that the sorption isostere of He-4 is anomalous at temperatures close to the temperature of the phase transition in the bulk of He-4, T(lambda). An abrupt pressure change is observed for a He-4 film thickness approximately equal to two monolayers. The experiments on cryosorption of He-3 gas on an argon layer with a He-3 film thickness of approximately one monolayer display monotonous changes in pressure over the entire temperature range. (Author)