sensitivity great article very useful one thing that seems missing is discussion of how sensitive these things are and what sample size they need i was speculating about the recent alexander litvinenko poisoning with polonium and presuming that one could use a mass spectrometer to date the age of the polonium as it decays to lead with a half life of only days one might thereby deduce on which day the polonium had been created it's a synthetic isotope however the question of how big a sample one might need and how sensitive the results might be came up and i was unable to find an answer