The density and pressure of helium in bubbles in metals

Abstract

The energy shift of the He 1¹S₀−2¹P₁ transition, ΔE(n), can be used to determine the density, n, of He in bubbles in metals. A self-consistent band structure calculation for solid fcc He yields a linear relationship ΔE=C.n with C _th=22 × 10⁻³ eV nm³. Systematic electron energy loss spectroscopy and transmission electron microscopy studies of He bubbles in Al for various He doses and temperatures result in C_exp=(24±8).10⁻³ eV nm³ in agreement with theory. The analysis is consistent with the assumption that dislocation loop punching is the dominant bubble growth mechanism during high-dose room temperature implantation. The application to He bubbles in Ni indicates a maximum He density of n=0.2 × 10³ nm⁻³ for which He should be solid at room temperature.