Explanatory notes
… Section (IV) below, and certain isotopes of thallium, lead, bismuth, polonium, radium, actinium or thorium, which are … which they were derived by radioactive conversion. Thus, bismuth 210 is called radium E , polonium 212 is called … highly radioactive isotopes (0.3 x 10 -6 for thorium C’) to billions of years (1.5 x 10 11 years for samarium 147) and …