Reply to comment by F. Yaron ) 7on 'excess 234U: an aging effect in confined waters'{. )]

There are two mechanisms that can separate uranium isotopes in nature. One is a chemical mechanism, which preferentially leaches 234U relative to 238U. The other introduces 234U by the physical ejection of a parent 234Th across phase boundaries and is independent of aqueous chemistry. Kigoshi was referring to the first method in explaining the excess 234U that he obtained in his leachates. The degree of selective leaching that he reports is in good agreement with previous work. It is the second mechanism that he uses to explain the high 234Th excess activity. It is felt that the waters used are analogous to the aqueous complement of the anomalous solid sample reported by Sakanoue and Komura, in which thorium isotopes ejected and precipitated on the crystal surface gave rise to a 234U/238U ratio of approximately 15 and a 230Th/238U activity ratio of about 150. (Auth.)