Statistical chronometry of Meteorites: II. Initial abundances and homogeneity of short-lived radionuclides

摘要: Astrophysical models of planet formation require accurate radiometric dating of meteoritic components by short-lived (Al–Mg, Mn–Cr, Hf–W) and long-lived (Pb–Pb) chronometers, to develop a timeline of such events in the solar nebula as formation of Ca-rich, Al-rich Inclusions (CAIs), chondrules, planetesimals, etc. CAIs formed mostly around a time (“t= 0”) when the short-lived radionuclide 26 Al (t 1/2= 0. 72 Myr) was present and presumably homogeneously distributed at a known level we define as (26 Al/27 Al) SS≡ 5. 23× 1 0− 5. The time of formation after t= 0 of another object can be found by determining its initial (26 Al/27 Al) 0 ratio and comparing it to (26 Al/27 Al) SS. Dating of meteoritic objects using the Mn–Cr or Hf–W systems is hindered because the abundances (53 Mn/55 Mn) SS and (182 Hf/180 Hf) SS at t= 0 are not known precisely. To constrain these quantities, we compile literature Al–Mg, Mn–Cr, Hf …