This International Standard covers the techniques for the quantification of the activity of identified radionuclides using any of a variety of ionization chambers currently available for this purpose. The application of the standard is limited to instruments that incorporate well-type ionization chambers as detectors. This standard provides a method for obtaining measurements that are accurate to within ±10 % and reproducible to within ±5 % (usually for sources of more than 3,7 x 10 6 Bq (100 pCi)).