Effect of theλTransition on the Atomic Distribution in Liquid Helium by Neutron Diffraction

Abstract

Neutron diffraction patterns for samples of liquid helium at 1.06°K, 2.29°K, and 2.46°K have been measured over the angular range 4° to 64° using ${1.06}_4$ A neutrons. The liquid structure factor $i\left(s\right)+1\mathrm{}$ was deduced for each curve and these show a change which is associated with the $\lambda$ transition which indicates that the spatial order in the liquid is smaller below the $\lambda$ point than above. The measurements were transformed to give the radial distribution function $4\pi r^2\left[\rho \mathrm{}\right(r)-{\rho }_0]$ from which was deduced the number of neighbors under the first shell of atoms and the nearest distance of approach of two atoms in the liquid. These lie between $8_{.5}$ atoms and $9_{.8}$ atoms and 2.35 A and 2.40 A, respectively.