Reply #103: There is a typo in this post.

[NNadir]

I have inadvertantly written an equation in differential form that should not be in that form.

The correct equation for the accumulated isotope of interest should be written N = Nmax*(1-exp(-kt)) not dN = Nmax*(1-exp(-kt)). Moreover my wording was bad and I made it seem as if this relationship gives the amount of new isotopes formed. This is not the case. The new isotope formed in each year is the difference for the accumulated values for subsequent years. To wit:

dN(t1,t2) = Nmax*(1-exp(-k(t2))) - Nmax*(1-exp(-k(t1))) where t2 and t1 are the times given in years between measurements of total accumulations.

Here I have written dN merely to represent a changing value, and strictly this is not a differential equation. If a delta were available in this editor, I would substitute a delta for the d.

Even though I wrote the formulas incorrectly in the post text, the values in the described spreadsheet were calculated using the correct formulas. Thus there is no change in any of the results posted. But the transcription of the formulas into written language was done sloppily, for which I apologize.