a method for measuring he rate of decay of a radioactive isotope, frequently a beta-emitter, in which the material containing the isotope is converted to a liquid called a scintillant. The scintillant contains molecules of a radioactive (radioactive), which fluoresce when excited by a transfer of energy, from, for example, an emitted beta-particle. The resultant emission of light quanta (radioactive of light), the number of which is proportional to the total energy of the initiating beta-particle, are registered as a simple pulse by a closely placed radioactive tube (or tubes). The number of pulses counted in unit radioactive (the counting rate) is thus related to the disintegration rate (activity) of the sample being measured.