Originally published in Nnturc 125, 744 (1930) 



15. SEARCH FOR AN INACTIVE ISOTOPE OF 

 THE ELEMENT 84 (POLONIUM) 



G. Hevesy and A. Guenther 

 From the Institute of Physical Chemistiy, University- of P'reiburg 



The elements 81 (thallium), 82 (lead), and 83 (bismuth) have both 

 radioactive and inactive isotopes, whereas the elements 84 — 92 are only 

 known in an active form. Several attempts have been made to find 

 inactive isotopes of the latter elements. Aston, using his mass spectro- 

 graph, tried to discover a stable isotope of radon in the atmosphere, 

 and Hahx made extensive researches to find an inactive isotope of 

 radium. All these attempts failed. 



We have recently tried to extend the series of inactive elements by 

 searching for an inactive isotope of the element 84 (polonium), which 

 follows bismuth. Through the work of the discoverer of this element. 

 Mme. Curie, and her co-workers, as avcH as of Marckwald and of 

 many others, the chemical properties of polonium were found to be 

 intermediate between those of bismuth and tellurium. Hence it is obvious 

 that if a stable isotope exists, it must be associated in nature with 

 tellurium or bismuth. 



We looked for the elements 84, therefore, in the following tellurium and 

 bismuth minerals : Hessite, calaverite, nagyagite, tetradymite, and 

 bismuth glance as well as native bismuth. The minerals were dissolved, 

 and a known amount of polonium added as radioactive indicator. On 

 removal of the polonium from the solution, it was to be assumed that 

 any isotope present in the solution would accompany the active polo- 

 nium. By special methods devised for the purpose, it was possible to 

 legain the added polonium electrolytically on molybdenum electrodes, 

 the deposit weighing only about 1/10 mgm. X-ray investigations, carried 

 out by the secondary ray method to avoid the possible volatilisation oi" 

 the substance under the action of the cathode rays, have shown that the 

 deposit cannot contain more than 1/2 per mille of the element looked 

 for. The X-ray line searched for was polonium L^^ , the wave-length of 

 which was calculated from Moseley's law to be 1111 X. U. All the lines 

 on the plate could be identified as belonging to lead, bismuth, silver, 

 mercury, or tungsten. As we started with about 400 grams of each of the 

 minerals mentioned, 1 gm of each mineral cannot contain more than 10-" 



