Solve for any unknown in radioactive decay calculations
N(t) = Nâ‚€ Ă— (1/2)^(t/t_half)
t = t_half Ă— ln(Nâ‚€/Nt) / ln(2)
t_half = t Ă— ln(2) / ln(Nâ‚€/Nt)
λ = ln(2) / t_half