S is made by neutron bombardment of Cl 
:Cl + n → S + p
It decays by beta-decay with a half-life of 87.51 days. It is used to label the sulfur-containing amino-acids methionine and cysteine. When a sulfur atom replaces an oxygen atom in a phosphate group on a nucleotide a thiophosphate is produced, so S can also be used to trace a phosphate group.