Half-life measurements with ionization chambers--a study of systematic effects and results.

Accurate half-lives have been determined at the Physikalisch-Technische Bundesanstalt (PTB) using ionization-chamber measuring systems to assure the quality of radioactivity standards over the period of their use as detector calibrants or other purposes such as nuclear medicine and environmental monitoring. Some long-lived radionuclides have been measured for up to 28 years: 85Kr, 90Sr, 108Agm, 133Ba, 152Eu, 154Eu, and more recently 65Zn, 106Ru, 109Cd and 137Cs; short-lived radionuclides have also been studied such as: 18F, 67Ga, 81Rb, 99Mo, 99Tcm, 103Pd, 111In, 123I, 131I, 153Sm, 169Er, 177Lu, 186Re, 188Re, 201Tl, 222Rn and 224Ra. Relative uncertainties of half-life values of the order of 5 x 10(-4) were obtained. These values are compared to the results of other measurements and evaluations, and the limiting systematic effects are discussed.