Phosphorus-32

Phosphorus-32 decays purely by beta-minus emission (no gamma) with a half-life of 14.27-14.29 days, releasing 1.71 MeV of decay energy with an average beta energy of about 0.695 MeV, to stable sulfur-32. It has no gamma component, so it cannot be imaged with a gamma camera, and is entirely unsuitable for a diagnostic pairing.

As inorganic sodium phosphate, 32P has been used since 1939 to treat polycythaemia vera and other myeloproliferative disorders, where rapidly dividing marrow cells take up phosphate; as 32P-chromic phosphate colloid, it has been instilled directly into the peritoneal or pleural cavity to palliate malignant ascites or effusions, since colloidal particles are largely retained locally and irradiate the serosal surface. It is one of the oldest therapeutic radionuclides in clinical use and is classified by IARC as carcinogenic to humans (Group 1) based on its therapeutic use.

32P is made in a reactor, most commonly by fast-neutron irradiation of sulfur-32 via the 32S(n,p)32P reaction (chosen because it avoids diluting the product with large amounts of inactive phosphorus), or alternatively by thermal-neutron capture on phosphorus-31, 31P(n,γ)32P. Because of its short half-life it cannot be stockpiled and must be used soon after production, but as a simple, long-established reactor product it is not considered supply-constrained.