Effect of the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>λ</mml:mi></mml:math>Transition on the Atomic Distribution in Liquid Helium by Neutron Diffraction

Abstract

Neutron diffraction patterns for samples of liquid helium at 1.06\ifmmode^\circ\else\textdegree\fi{}K, 2.29\ifmmode^\circ\else\textdegree\fi{}K, and 2.46\ifmmode^\circ\else\textdegree\fi{}K have been measured over the angular range 4\ifmmode^\circ\else\textdegree\fi{} to 64\ifmmode^\circ\else\textdegree\fi{} using ${1.06}_{4}$ A neutrons. The liquid structure factor $i(s)+1$ was deduced for each curve and these show a change which is associated with the $\ensuremath{\lambda}$ transition which indicates that the spatial order in the liquid is smaller below the $\ensuremath{\lambda}$ point than above. The measurements were transformed to give the radial distribution function $4\ensuremath{\pi}{r}^{2}[\ensuremath{\rho}(r)\ensuremath{-}{\ensuremath{\rho}}_{0}]$ 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.