Phosphorus-32 (32P) is a radioactive isotope of phosphorus. The nucleus of phosphorus-32 contains 15 protons and 17 neutrons, one more neutron than the most common isotope of phosphorus, phosphorus-31. Phosphorus-32 only exists in small quantities on Earth as it has a short half-life of 14 days and so decays rapidly. Phosphorus is found in many organic molecules and so phosphorus-32 has many applications in medicine, biochemistry, and molecular biology where it can be used to trace phosphorylated molecules (for example, in elucidating metabolic pathways) and radioactively label DNA.