Method of measuring the disintegration rate of beta-emitting radionuclide in a liquid sample

A method of measuring the disintegration rate (DPM) of a beta-emitting radionuclide in a liquid sample using a scintillation counting system, comprising the steps of:

• a. exposing the sample to radiation from a standard source and generating a pulse height distribution spectrum for the sample in the presence of the standard source,
• b. detecting a unique point on the spectrum and measuring the corresponding pulse height value (PH.sub.1),
• c. counting pulses produced by the radionuclide in the sample (CPM.sub.1) in a window bounded on one side by a zero pulse height threshold detection limit for the counting system and bounded on the other side by a limit the value of which at least includes all the pulses produced by the radionuclide in the sample,
• d. developing a quenched version of the sample,
• e. exposing the quenched sample to radiation from the standard source and generating a pulse height distribution spectrum for the quenched sample in the presence of the standard source,
• f. detecting the unique point on the latter spectrum and measuring the corresponding pulse height value (PH.sub.2),
• g. counting pulses produced only by the radionuclide in the quenched sample (CPM.sub.2) in said window,
• h. developing normalized values (R.sub.1, R.sub.2) for the measured pulse heights (PH.sub.1, PH.sub.2), and
• i. correlating the normalized values (R.sub.1, R.sub.2) with corresponding pulse counts (CPM.sub.1, CPM.sub.2) to determine the value of the pulse count (CPM.sub.0) for a normalized pulse height value of zero (R.sub.0).