2006 Volume 55 Issue 10 Pages 567-575
The activity ratio of 228Ra/226Ra in leachate from monazite was observed to decrease with increasing pH of the solution, while those of 224Ra/ 228Ra, 230Th/232Th and 228Th/232Th increase with increasing pH. The leaching behavior of 226Ra and 224Ra which are formed through 5 decay processes of 238U and through 4 decay processes of 232Th, respectively, was different from that of 228Ra which is formed by a single decay of 232Th. Thorium isotopes, 230Th and 228Th, decay products of 238U and 232Th, respectively, were also leached more effectively than 232Th. The leaching efficiency of Ra and Th isotopes was estimated to be dependent on the difference in the history of decay processes which have formed the nuclides.