= Phosphorus-32
{title2=$^{32}\mathrm P$}
<Phosphorus-32> is a radioactive <isotope> of <phosphorus> with 15 <protons> and 17 <neutrons>. It undergoes <beta-minus decay> to <sulfur-32>, preserving the mass number while increasing the <atomic number> by one. The cited laboratory evaluation gives a <half-life> of $14.273(7)\,\mathrm d$.<Phosphorus-32 in LNE-LNHB Table de Radionucleides>[Page1, decay scheme and nuclear data; March2026 evaluation]{ref}
Its <radioactivity> makes phosphorus-containing material experimentally traceable. In the 1952 <Hershey-Chase experiment>, <phosphorus-32> labelled the <DNA> component of <Bacteriophage T2>. Mechanical agitation removed much less phosphorus label than sulfur label from infected <bacteria>, helping distinguish the material entering the cells from material remaining at the surface.<Independent functions of viral protein and nucleic acid in growth of bacteriophage by A. D. Hershey and Martha Chase>[Abstract, points4–6: label separation and progeny comparison]{ref} The interpretation relies on the labelling and separation in this system; it is not a rule that all biological phosphorus belongs to DNA.
For a closed sample changing only by <radioactive decay>, $A(t)/A(0)=2^{-t/T_{1/2}}$. After two quoted <half-lives>, about 28.546 days, the <radioactivity> is one quarter of its initial value. A falling signal can therefore reflect decay even without loss of labelled material from a vessel. Movement of material, chemical processing and detector response require additional measurements when interpreting a real tracer experiment.
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