Production of technetium in red giants by γ- ray-induced fission

Abstract

The discovery of technetium in red giant stars¹ was a landmark in stellar nucleosynthesis theory. Because of the short half-lives of its isotopes, the presence of technetium has been regarded as irrefutable evidence for a recent episode of slow-neutron capture ('s-process') in asymptotic giant branch stars^2–6. But the 100 or so stars with technetium lines in their spectra^{7, 8} (Tc stars) show the opposite correlation between metallicity and technetium production to that expected to result^{3, 4 ,9} from an s-process. Here we argue that the production of technetium in red giant stars is not necessarily related to an interior s-process mechanism, and that some observations of technetium in metal-rich (population I) red giants may be more readily explained by γ-ray-induced fission of heavy isotopes (atomic mass A≈ 240) initially present in the stellar envelope.