Accurate equation of state of H2-He binary mixtures up to 5.4 GPa

Brillouin scattering spectroscopy has been used to obtain an accurate (<1%) rho-P equation of state (EOS) of 1:1 and 9:1 H-2-He molar mixtures from 0.5 to 5.4 GPa at 296 K. Our calculated equations of state indicate close agreement with the experimental data right to the freezing pressure of hydrogen at 5.4 GPa. The measured velocities agree on average, within 0.5%, of an ideal mixing model. The rho-P EOSs presented have a standard deviation of under 0.3% from the measured densities and under 1% deviation from ideal mixing. A detailed discussion of the accuracy, precision, and sources of error in the measurement and analyses of our equations of state is presented.