technique used to track the passage of an isotope (an atom with a detectable variation in neutron count) through a reaction, metabolic pathway, or cell, and the reactant is 'labeled' by replacing specific atoms by their isotope, tehnika, mida kasutatakse isotoobi (aatomi, mille neutronite arv on tuvastatava muutusega) liikumise jälgimiseks reaktsiooni, metaboolse raja või raku kaudu, kusjuures reagent on „märgistatud“, asendades spetsiifilised aatomid nende isotoobiga tekitades nn isotoopindikaatori, technique used to track the passage of an isotope (an atom with a detectable variation in neutron count) through chemical reaction, metabolic pathway, or a biological cell