By quantum effects becoming important, I mean they begin to significantly affect thermodynamic properties of the gas, such as the magnitude of the second virial coefficient B(T).

I can calculate things like the thermal de Broglie wavelength, the de Boer parameter, etc., but I was wondering if there was some straightforward way to estimate this. Presumably for rare gas atoms with weaker interactions (Helium) the "quantum temperature" should be larger than that for rare gas atoms with strong interactions (eg, argon).

Thank you - I hope I am clear!