The density dependence of the electron surface barrier for ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ and ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ fluids has been determined by injection of electrons from a planar gold surface into the liquid and the dense vapor phases. Barrier values for both isotopes are consistent with a Wigner-Seitz calculation for atomic densities up to the experimental limit of 1.8 × ${10}^{22}$ ${\mathrm{cm}}^{-3\mathrm{}}$ (${}_{}{}^3{}_{}{}^{}\mathrm{He}$) and 3.0 × ${10}^{22}$ ${\mathrm{cm}}^{-3\mathrm{}}$ (${}_{}{}^4{}_{}{}^{}\mathrm{He}$). Comparison of results with other theoretical and experimental values is presented.

• Received 14 July 1975

DOI:https://doi.org/10.1103/PhysRevB.14.2819