Neutron Small Angle Scattering on Liquid Helium in the temperature Range 1.5-4.2 K

TL;DR

This study used neutron scattering to examine liquid helium's microscopic structure across 1.5-4.2 K, revealing a smooth zero-angle cross section but a notable change in the pair correlation function's slope at the superfluid transition.

Contribution

First neutron scattering measurements across the lambda-point showing structural changes in liquid helium during the superfluid transition.

Findings

Zero angle cross section decreases monotonically with temperature.

No singularity observed at the lambda-point in the cross section.

Change in slope of the second momentum of the pair correlation function at lambda-point.

Abstract

The small angle neutron scattering from liquid helium at saturated vapour pressure in the temperature range from 1.5 to 4.2 K was measured with the instrument D22 of the ILL Grenoble at a wavelength of 4.6 angstrom. The zero angle cross section is monotonically decreasing with decreasing temperature and does not show any singularity at the lambda-point. On the other handd, we observe a change of the slope of the temperature dependence of thw second momentum of the pair correlation function at the lambda-point that reflects the transition of liquid to the superfluid state.