142 ADVENTURES IN RADIOISOTOPE RESEARCH 



Comment on paper 15 



The search for unknown elements is much facilitated by adding a radioacti\(' 

 isotope of the desired element to the solution of minerals in which the element 

 is most hkely to be present. In paper 15 the conclusion was reached that a heavier 

 stable element than bismuth is unlikely to be found. This conclusion is supported 

 by later experience. 



In an earlier investigation carried out in 1926 in Copenhagen an unsuccessful 

 search was made for a stable isotope of the element 87 by trying to detect a-rays 

 emitted by MsThj or )S-rays by radon. Both processes should lead to the formation 

 of the element 87. A radioactive isotope of this element was later discovered 

 by Perey and Lecoin. A more detailed presentation of the results stated in 

 paper 15 is to be found in Z. f. anorg. Chem. vol. 194. 



References 



G. Hevesy (1926) Kgl. Danske Vid. Selsk. Mathem.-fysiske Medd. 7, 11. 



M. Perey and I- Lecoin (1939) Nature 144, 326. 



G. Hevesy and A. Guenther Z. /. anorg. Chem. 194. 162 (1930). 



