Tritium (hydrogen-3) is a very low beta energy emitter that can be used to label proteins, nucleic acids, drugs and almost any organic biomolecule. The maximum theoretical specific activity of tritium is . However, there is often more than one tritium atom per molecule: for example, tritiated UTP is sold by most suppliers with carbons 5 and 6 each bonded to a tritium atom.
For tritium detection, liquid scintillation counters have been classically employed, in which the energy of a tritium decay is transferred to a scintillant molecule in solution which in turn gives off photons whose intensity and spectrum can be measured by a photomultiplier array.  The efficiency of this process is 4–50%, depending on the scintillation cocktail used. 
  The measurements are typically expressed in counts per minute (CPM) or disintegrations per minute (DPM).  Alternatively, a solid-state, tritium-specific phosphor screen can be used together with a phosphorimager to measure and simultaneously image the radiotracer. Measurements/images are digital in nature and can be expressed in intensity or densitometry units within a region of interest (ROI).