The State of 7Be in the Sun

Abstract

The ionization state of 7Be in the solar core affects the prediction of the solar 8B neutrino flux. Recently, Shaviv & Shaviv (2003) examined the theory and the effect of pressure ionization on the ionization state of 7Be and all elements with 12 ⩾ Z ⩾ 4. It was shown that under the conditions prevailing in the solar core, the ionization state is determined mainly by the nearest neighbor and not by the Debye potential created by the entire plasma.As pressure ionization is determined mainly by the nearest neighbor, we first redefine the ion‐sphere for a mixture and then solve the Schrödinger and later the Kohn‐Sham equations for an ion immersed in a dense plasma under conditions for which the mean interparticle distance is smaller than the Debye radius.Contrary to previous estimates showing that Beryllium is partially ionized, we find that it is fully ionized. As a consequence, the predicted rate of the 7Be + e− reaction is reduced by 20–30%, quite insensitive to the exact solar model. Since 7Be is a trace element, its total production is controlled by the unchanged 4He +3 He reaction rate, and its destruction is determined by the rate of electron capture. As the latter rate decreases when the Beryllium is fully ionized (relative to the case of partially ionized Be), the estimate for the abundance of 7Be increases and with it the 8B neutrino flux. The increase in φv(8B) is by about 20 – 30%. The neutrino flux due to Be7 electron capture remains effectively unchanged because the change in the rate is compensated for by a change in the abundance. The prediction for the ratio of φv(8B)/φv(7Be) changes as well.