An extensive search for emission from the 8.7 GHz hyperfine line of ³He⁺ in 17 Galactic H II regions has yielded new detections in six regions and significant upper limits for the others. The authors derive the (³He/H) abundance ratios for their sources and find the largest (³He/H) abundance ratio is more than 10 times greater than their smallest limit. This observation gives strong support for source-to-source variations. There is a marginal tendency for sources outside the solar circle to have larger abundances. For the nine sources where ³He⁺ was detected, the average (³He/H) abundance ranges from 1.2 to 14.7×10⁻⁵ by number; for sources with limits, the lowest values are about 1×10⁻⁵. The authors discuss briefly the utility of ³He⁺ as a probe of cosmology or the chemical evolution of the Milky Way.
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Bania et al. (1987) studied this question.