Radiochemical isolation and radioactivity calibration of radium-228 by liquid-scintillation counting and gamma-ray spectrometry

228Ra was separated from aged thorium nitrate by liquid-liquid, two-phase extraction and was extensively purified, principally by ion-exchange chromatography. The radioactivity concentration of the purified 228Ra was measured by means of liquid-scintillation #betta#-particle measurements of the 228Ac daughter (corrected for progeny ingrowth). The results were confirmed by Ge(Li) well-detector intercomparison with 228Ra in equilibrium with its 232Th precursor which had been measured gravimetrically. Three hundred ampoules were provided to the U.S. Environmental Protection Agency, Las Vegas, for distribution. (author)