Density of superfluid helium droplets

The classical integral cross sections of large superfluid ⁴HeN droplets and the number of atoms in the droplets (N=10³-10⁴) have been measured in molecular beam scattering experiments. These measurements are in good agreement with the cross sections predicted from density functional calculations of the radial density distributions. By using a simple model for the density profile a 10--90 % surface thickness of about 6--8 {} is extracted directly from the data.