Transmission of Slow Neutrons by LiquidHe4. II

Abstract

The Los Alamos slow-neutron total scattering cross sections in liquid ${\mathrm{He}}^4$ are analyzed using the general scattering theory expected to be valid at short and medium neutron wavelenths. With the approximate mean kinetic energies and partial mean square forces per liquid atom derived previously, the theory is in fair agreement with the data below about 8 A; it breaks down at longer wavelengths. The analysis of the data is then inverted by attempting to solve the following problem: is it possible to find with the cross-section data a set of liquid parameters, at a given liquid temperature, such that the cross sections computed with them would represent the data at wavelengths larger than 8-9 A. This problem receives an affirmative solution inasmuch as the neutron data liquid parameters turn out to be in fair agreement with the approximate liquid parameters obtained by an entirely different method. The scattering cross sections recalculated with the new parameters represent the data fairly well out to 12-13 A. A direct, practically experimental, proof has been obtained for the existence of a very large zero-point kinetic energy in liquid ${\mathrm{He}}^4$ over a wide temperature interval. The significance of these results for the derivation, with neutron and x-ray data, of mean kinetic and potential energies, and mean square forces, per atom, in liquids is discussed.