The Oxygen to Carbon Ratio in the Solar Interior: Information from Nuclear Reaction Cross-Sections

Mass separation in the Sun may explain a serious difficulty that has plagued nuclear astrophysics for decades: Why the oxygen to carbon ratio in the Sun’s photosphere is only two, O/C ≈ 2. After correcting for mass fractionation, the ratio of these helium-burning products in the Sun is much larger, O/C ≈ 9–10. The lower value, O/C ≈ 9, is probably more reliable. It is based on measurements of mass separation of stable noble gas isotopes in the solar wind over the mass range of 3–136 amu. The higher value, O/C ≈ 10, is based on a comparison of neutron-capture cross-sections and the abundances of s-products in the photosphere over the mass range of 25–207 amu. Both methods indicate that Fe, Ni, O, Si, and S are the most abundant elements in the Sun. These elements are produced in the deep interior of supernovae.