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 210 and presuming that one could use a Mass Spectrometer to date the age of the Polonium 210 as it decays to Lead 206 with a half life of only 138 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