Standards of radium-226: from Marie Curie to the International Committee for Radionuclide Metrology.

In the early part of the 20th century, the pioneers of radioactivity research, led by Marie Curie, Ernest Rutherford and Stefan Meyer, formed a Commission internationale des étalons de radium. The Commission made arrangements for the preparation and intercomparisons of the international standards of radium, which were identified as the Paris standard and the Vienna standard. Otto Hönigschmid from Vienna prepared a first set of international secondary standards in 1912 and a second set in 1934. In both instances, these secondary standards were compared by gamma-ray measurements with the Paris and Vienna standards. The usage of these international standards of radium in the 20th century is described.