P is made by neutron bombardment of S
:S + n → P + p
It decays by beta decay with a half-life of 14.29 days. It is commonly used to study protein phosphorylation by kinases in biochemistry.
P is made in relatively low yield by neutron bombardment of P. It is also a beta-emitter, with a half-life of 25.4 days. Though more expensive than P, the emitted electrons are less energetic, permitting better resolution in, for example, DNA sequencing.
Both isotopes are useful for labeling nucleotides and other species that contain a phosphate group.