Possible experimental test for determination of the role of microscopic vortex rings in the l-transition in helium II

An experimental test is proposed to clarify the question, whether the microscopic vortex rings (MVR) play an important role in the λ-transition in helium-II. It is suggested that in the He II bulk, there exists an ensemble of vortex rings which induce the λ-transition and define substantially the value of Tλ. For very thin films of He II of superfluid layer thickness d less than the size d0 of the smallest MVR, the rings do not fit in and do not exist in such films. As a result, for the films of helium II on disordered substrates the curve Tλ(d) should display, a jump-like peculiarity d approxd0 approx (6+-4) A. The currently available experimental data on specific heat of thin films of He II are insufficiently complete and precise for the conclusion about the presence or absence of the predicted peculiarity