text: Phosphorus-32 is widely used for labeling nucleic acids and phosphoproteins. It has the highest emission energy (1.7 MeV) of all common research radioisotopes. This is a major advantage in experiments for which sensitivity is a primary consideration, such as titrations of very strong interactions (i.e., very low dissociation constant), footprinting experiments, and detection of low-abundance phosphorylated species. Phosphorus-32 is also relatively inexpensive. Because of its high energy, however, its safe use requires a number of engineering controls (e.g., acrylic glass) and administrative controls.  The half-life of phosphorus-32 is 14.2 days, and its maximum specific activity is .
  Phosphorus-33 is used to label nucleotides. It is less energetic than phosphorus-32 and does not require protection with plexiglass. A disadvantage is its higher cost compared to phosphorus-32, as most of the bombarded phosphorus-31 will have acquired only one neutron, while only some will have acquired two or more. Its maximum specific activity is .