X-RAY SCATTERING FROM LIQUID HELIUM

We have measured the liquid structure factor S(k) for liquid He4 and for liquid He3 by x-ray diffraction. Our results for liquid He4 agree with the Feynman formula k2mc in the range 0.3<k<0.6 -1, in contrast to previous measurements of S(k) which fell about 25% below k2mc in this range. The peak in the pair distribution function g(r) derived from the scattering data occurs at greater interatomic distance and is lower, broader, and less symmetrical for liquid He3 than for liquid He4, in agreement with predictions based on variational calculations. However, the experiments indicate slightly more structure in both liquids than the calculations predict. We have also measured S(k) for He4 vapor at 4.2 K, 0.98 atm. For He4 vapor, g(r) shows a distinct nearest-neighbor shell and probably a second-nearest-neighbor shell. © 1969 The American Physical Society.