Galactic cosmochronology

Rutherford (1929) noted that the abundance ratio 235u/238U is 0.007 now and was 0.3 at the birth of the Solar System, and he pointed out that extrapolation still further back to the (mean) epoch of nucleosynthesis would give the production ratio the assumption at that time was that elements had been synthesized in the Sun and that the planets were formed out of material extracted from the Sun by a passing star. Reasoning that the production ratio was likely to be a reasonably small number ( 10, say), he deduced that the mean nucleosynthesis epoch could not have been more than 4.3 Gyr before the formation of the Solar System. 

1 An illustration of the relevant tracks in the (N, Z) plane is given by Thielemann, Metzinger and Klapdor (1983). 

ISOLATION OF SOLAR CLOUD LATE INJECTION OF 26AI EARLY SOLAR SYSTEM MATERIAL 

We assume that actinides are formed along with other elements in some sort of GCE history during a period of time A up to the formation of the Solar System (Fig. 10.2). Thus 

In the theoretical development, we assume instantaneous recycling with constant yields and generalize Eq. (7.34) to the case of a decaying element with Zp = 0 using now time as the independent variable, bearing in mind that E = t]onff and neglecting free decay  

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Galactic cosmochronology and stellar thorium abundances theory... 

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