Activity standardisation of ²²⁶Ra by 4πα liquid scintillation counting method.

Activity of (226)Ra in radium daughter products free solution was determined by 4πα liquid scintillation counting (LSC) method, where the detection efficiency of radium decay is practically equal to 1. The sources were prepared from solution with known (226)Ra mass concentration, from which, immediately before LS counting, (222)Rn and its daughter nuclides were removed by solvent extraction. LS counting results were corrected practically only for a <0.6% loss of radium from measured sample and for the ingrowth of (222)Rn and (218)Po concentrations in the sample after the separation was completed. The combined relative standard uncertainty was estimated to be lower than 0.34%.