312 BELL SYSTEM TECHNICAL JOURNAL 



in Nature) : how will the unstable nucleus resolve its dilemma? Such 

 cases are rare, but not entirely absent. An example appears in Fig. 12. 

 The elements palladium and cadmium have isobaric isotopes of mass- 

 number 106, in spite of the fact that their atomic numbers (46 and 48) 

 are not consecutive; silver, with atomic number 47, lies between. 

 There is no stable silver isotope 106, but a radioactive one can be and 

 has been created, and for this the dilemma is posed. It handles the 



O 



O O 



O 



Fig. 12 — Illustrating an example of isomers. 



dilemma by grasping both horns! electrons of both signs come out of 

 the radioactive silver. I must say that there is something which 

 indicates that the nuclei which make one choice may be slightly 

 different (in mass, for instance) from those which make the other. 

 It may therefore be well to speak of silver as having two isotopes of 

 the same mass-number 106, and a word has already been coined: 

 they are called "isomers" of one another. This does not alter the 

 fact that where alternative choices exist, both are elected. 



On Fig. 2 we notice an arrow which points to a vacancy. No 

 stable nucleus Be^ is known, though there has been a very diligent 

 search for it conducted by many ways in many places. Practically 

 no doubt exists that Be^ bursts of itself into two pieces (two alpha- 

 particles) almost as soon as it is made. We thus have here an unstable 

 (radioactive) nucleus — Li^ — which does not find stability by ejecting 

 an electron, but instead hastens onward to a completer ruin. In the 

 lower reaches of the Table of the Elements there are so many stable 

 isotopes that the unstable ones can almost always turn themselves 

 by one electron-emission into one or another of these, and such 

 catastrophes are rare. Among the natural radioactive substances in 

 the upper reaches of the Table they are common, as I now show in 

 returning to natural radioactivity for the close of this talk. 



Notice again Fig. 4, in which the stars are so many and the circles 

 so few. If arrows were to be inserted to show the transformations, 

 they would crisscross into a maze. I have therefore separated the 

 figure into three: all of the circles, stars and rosettes in it will be found 



