Krypton mean free path

In the pressure range useful for krypton adsorption the mean free path is approximately equal to the diameter of the stem of the sample cell. Equation (14.16) is not applicable in this range and an empirical equation devised by Rosenberg must be used. His equation is... 

At what pressure does the mean free path of krypton (Kr) atoms (d = 3.16 X 10 ° m) become comparable with the diameter of the 1-L spherical vessel that contains them at 300 K Calculate the diffusion constant at this pressure. 

Assume that the hard-sphere radius of a krypton atom is 1.85 A. Estimate the mean free path of krypton atoms at 20.0°C and 1.00 bar pressure. 

---