The 226Ra (50 Bq mL-1) and 133Ba (100 Bq mL-1) standard were obtained from the National
Physical Laboratory (NPL) and Amersham Pharmacia Biotech UK Limited, respectively. The
stable Ba2+ solutions were prepared from standard solution 1000 mg L-1 (Fisher Scientific®). All
other chemicals used in this study were of analytical grade and all solutions were prepared with
super pure water.