Time-resolved spectral radiation histories of the gaseous H(2) + He mixtures under shock loadings were measured by using a six-wavelength channel pyrometer. The initial gaseous mixtures had a mole component of H(2):He = 1:1.21, which were shocked from room temperature and initial pressure of 20 MPa to a pressure range of 1-30 GPa and temperature range of 3000-7000 K by means of a two-stage light-gas gun. Multishock reverberations between the base-plate and sapphire window can be observed up to the fifth-shock compressions. The experimental data are in good agreement with self-consistent fluid variational theory calculations in which the dissociation process of hydrogen molecules and various interactions among atomic and molecular species are taken into account.

The fluid variational theory is used to calculate the Hugoniot equation of state (EOS) of He, D 2 , He + H 2 , and He + D 2 fluid mixtures with different He:H 2 and He:D 2 compositions at high pressures and temperatures. He, H 2 , and D 2 are the lightest elements. Therefore, the quantum effect is included via a first-order quantum correction in the framework of the Wigner-Kirkwood expansion. An examination of the reliability of the above computations is performed by comparing experiments and calculations, in which the calculation procedure used for He and D 2 is adopted also for He + D 2 and He + H 2 , since no experimental data for the mixtures are available to conduct these comparisons. Good agreement in both comparisons is found. This result may be seen as an indirect verification of the calculation procedures used here, at least, in the pressure and temperature domains covered by the experimental data for He and D 2 used for comparisons, which is nearly up to 40 GPa and 10 5 K. Also, the equation of state of He + H 2 fluid mixtures with different compositions is predicted over a wide range of temperatures and pressures.