A possible relationship between extinct ²⁶Al and ⁵³Mn in meteorites and early solar activity

Abstract

Much excitement in the meteoritic and astrophysical communities has been raised by the discovery in a small fraction of the meteoritic material of isotopic anomalies ascribable to nuclear effects. A special class of those anomalies relates to the in-situ decay of now-extinct short-lived (t_(1/2) ≤ 10⁸ yr) radionuclides. One of the most important of those cases is ²⁶Al [(t_1/2) = 7.05 x 10⁵, following Norris et al. (1983)]. The short time scale for ²⁶Al has been used as the measure of time between the injection of freshly synthesized nuclei into a dense molecular cloud and its collapse. As reviewed by e.g. Wasserburg and Papanastassiou (1982), Wasserburg (1985) or Papanastassiou (1985), the (²⁶Al/²⁷Al)₀ abundance ratio at the time T₀ of crystallization is 5 x 10⁻⁵. Lower values have been found and are attributed to time differences or to heterogeneities in the solar nebula. There is some difficulty in maintaining large primary heterogeneities on the scale of 100 km in the solar nebula after collapse. There are also problems in relating the inferred abundances of short-lived nuclei with a simple or coherent set of nuclear astrophysical processes and sources. Strong evidence also exists for the presence of ¹⁰⁷Pd (t_(1/2) = 6.5 x 10⁶ yr) with (¹⁰⁷Pd/¹⁰⁸Pd)₀ = 2 x 10⁻⁵ in the early solar system (Kelly and Wasserburg 1978; Kaiser and Wasserburg 1983; Chen and Wasserburg 1983). As evidence of ¹⁰⁷Pd is found in iron meteorites, the time scale for this nuclide is related to the formation of small planetary objects.