Pulse shape analysis determines if two radiations are in coincidence. A transducer is provided that, when it absorbs the first radiation produces an output pulse that is characterized by a shorter time constant and whose area is nominally proportional to the energy of the absorbed first radiation and, when it absorbs the second radiation produces an output pulse that is characterized by a longer time constant and whose area is nominally proportional to the energy of the absorbed second radiation. When radiation is absorbed, the output pulse is detected and two integrals are formed, the first over a time period representative of the first time constant and the second over a time period representative of the second time constant. The values of the two integrals are examined to determine whether the first radiation, the second radiation, or both were absorbed in the transducer, the latter condition defining a coincident event.