316 BELL SYSTEAI TECHNICAL JOURNAL 



by being preponderantly the isotope 208 or the isotope 206 as the case 

 may be. 



I pause to mention, in justice to Rutherford, that it was he who 

 proved by study of some of these natural radioactive bodies that each 

 is transforming itself into a different element; also it was his associate 

 Soddy who by similar studies was led to distinguish the first-to-be- 

 recognized isotopes, that is, different radioactive forms of one and the 

 same element. The way for making such diagrams as Figs. 2 and 3 

 and 4 was prepared before 1914 by these two men, though some of 

 the facts embodied in Fig. 4 were not then available because of want 

 of knowledge of atomic numbers, and all of the knowledge embodied 

 in Figs. 2 and 3 was non-existent because no radioactive isotopes of 

 these elements had yet been created and nobody knew as yet how to 

 distinguish their stable isotopes. Also it should be mentioned that 

 only the extraordinary potency of radioactive substances in affecting 

 our instruments of measure enables the physicist or the chemist to 

 recognize the element to which a radioactive isotope belongs, nay even 

 to detect its presence. With radium and a few others, it has been 

 possible to amass enough of the substance to see and to weigh; with 

 the great majority of natural and with the totality of artificial radio- 

 active isotopes, nothing of the sort has even been approached, and we 

 should still be unacquainted '" with them if they had been stable. 



Three examples of transmutation which occur in these upper ranges 

 of the Periodic Table deserve to be recorded in even so brief a report. 



In Fig. 14, notice the circle in row 83 and column 209 which (as I 

 earlier said) represents the highest stable nucleus — ^bismuth 209. 

 Radium E, represented by the star to its right, is clearly bismuth 210; 

 by the testimony of its mass-number and atomic number, it differs 

 from stable bismuth nuclei by the possession of an extra neutron. 

 If bismuth should be bombarded by neutrons, either free or bound 

 into deuterons, would it be transformed into radium E? Livingood 

 at Berkeley did bombard ordinary bismuth with very energetic deu- 

 terons, and did succeed in producing a radioactive substance which 

 agreed with radium E not only in emitting negative electrons, but also 

 in converting itself into a substance emitting alpha-particles, and the 

 agreement extended to details of the emission. No doubt exists 

 that he was making radium E out of bismuth 209 by enabling deuterons 

 to transfer their constituent neutrons to this latter, just as H^ is made 

 from H^ in the first of the deuteron-deuteron reactions. 



1" This statement should be quaHfied slightly, for some of the artificial radioactive 

 nuclei spring from reactions of transmutation which are so well understood that the 

 observer could justifiably infer the existence of the nuclei in question even if he did 

 not observe them. 



