Counts per minute (cpm) is a measure of radioactivity. It is the number of atoms in a given quantity of radioactive material that are detected to have decayed in one minute. Disintegrations per minute (dpm) is also a measure of radioactivity. It is the number of atoms in a given quantity of radioactive material that decay in one minute. Dpm is similar to cpm, however the efficiency of the radiation detector (e.g. scintillation counter) must be accounted for when analysing data in cpm. Dpm is the number of atoms that have decayed, not the number of atoms that have been measured as decayed. Dpm is commonly used as a measure of radioactive contamination.