318 BELL SYSTEM TECHNICAL JOURNAL 



These were the natural radioactive bodies. To these forty kinds of 

 radioactive nuclei already found in Nature, physicists have added in 

 a scant four years no fewer than two hundred and twenty more by 

 the art of transmutation. Every chemical element which is known to 

 exist at all, with the sole exception of hydrogen, has at least one 

 radioactive type of nucleus or isotope, and many have more than one. 

 These man-made radioactive nuclei are often made simply by adding 

 neutrons to nuclei which already exist and are stable. There are, 

 however, other and more complicated processes, in which neutrons or 

 protons or deuterons or alpha-particles impinge on nuclei and seem to 

 enter them, and other particles leap out. Many radioactive bodies 

 have already been made in two or three different ways, some in as 

 many as five. 



Few things are riskier than to suggest a limitation either on the 

 scope of Nature or on the possibilities of science, and many a scientist 

 is remembered chiefly for such a suggestion which later the course of 

 events proved foolish. Yet there are circumstances in this case which 

 give some ground for suspecting that already we may know nearly 

 all of the stable and may have created nearly all of the radioactive 

 nucleus-types. Several hundreds of types have now been made by 

 the art of transmutation, but of them nearly all which seem to be 

 stable are not new, and nearly all which are new are radioactive. 

 This implies that the earth has already been stocked with almost all 

 the stable nucleus-varieties, but not necessarily that we have yet come 

 near to making all of the possible radioactive kinds. There are how- 

 ever reasons for believing that most of the remaining types have so 

 little durability, that even if they were to be made they would not 

 last long enough to be identified as radioactive. Nature probably 

 has come quite close to building all the imperishable forms, we possibly 

 almost as close to creating all of those which are capable of a little 

 but not a perpetual life. Perhaps it is fitting that people who are not 

 immortal should not be able to construct new elements which are 

 immortal; but we at least can rejoice in having diversified the scene 

 of the world with a surprising number of new substances which are 

 none the less remarkable for being transitory. 



