Abstract
Radial profiles of the light nuclei (A ≤15) are calculated in the non-mixing Sun, taking into account the changes of solar structure with time. The results are discussed in relation to models of solar mixing and compared with abundance determinations at the solar surface or in the solar wind. B cannot be depleted in the outer convective zone without producing a large increase in the He3/He4 ratio. A decrease in He3/He4 would be accompanied by changes in C13/C12 and N15/N14 of a magnitude which is not observed. It is shown that boron could be depleted in the pre-main sequence period of the Sun, if mixing was on a time-scale of 106 yr. The simultaneous small increase in He3/He4 does not contradict observation. However, Be would be depleted more strongly than B. A He3/He4 decrease is always accompanied by large changes in N15/N14 and C13/C12. Since such changes are not observed, it is concluded that the He3/He4 ratio in the outer convective zone is a reliable upper limit for (He3 + D)/He4 in the solar nebula. Thus the D/H ratio in the protosolar material was much lower than it is in sea water or in carbonaceous chondrites.
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