Structure studies in liquidHe4

We investigate, using neutron-diffraction data, several properties of the local atomic structure in liquid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$, both above and below the superfluid transition. Distinguishing features of the pair-correlation function are summarized and the diffraction data are employed to investigate a proposed form for the condensate fraction as a function of temperature. The pair-correlation function is used to examine an inequality that gives an upper bound that is close to the observed values, and also to examine the use of approximate integral equations for the ground-state wave function. Triplet correlations and closure approximations are studied from the isothermal density derivative of the pair-correlation function. The results suggest that, analogous to the pair-correlation function, the triplet-correlation function shows a temperature dependence that is not observed in simple classical fluids.