NUCLEAR FISSION 



By Karl K. Daekow 

 Bell Telephone Laboratories 



Some time this summer the art of transmutation will come to its 

 majority; that is to say, 21 years Avill liave passed since the day it was 

 born in Rutherford's laboratory. Infancy and adolescence for this 

 art have been marked by more stages than we generally count for 

 human children; I propose to distinguish six. Here follows a table 

 of six great events in the story of transmutation, beginning with birth 

 and ending with fission, which, by the way, bears a name that in 

 biology means a certain sort of birth. Each of them lifted the art to 

 a higher level with a broader scope. It is only the sixth and latest 

 which is my topic, but all the others lead up to it, as I will show 

 immediately with the table for my text. 



Table of great events in history of transmutation 



1919. First success with helium nuclei (energy of activation derived from 

 radium, etc.). 



1932. First success with hydrogen nuclei (energy of activation derived from 

 voltage). 



1932. Recognition of the liberated neutron. 



1934. Recognition of radioactive bodies resulting from transmutation. 



1934. Slow neutrons used to produce transmutation, this resulting in radioactive 

 bodies. 



1939. Recognition of fission. 



Be it said that, in general, transmutation takes place when two 

 nuclei meet and enter into a reaction with each other. They are made 

 to meet by projecting one against the other, and accordingly we 

 speak of one as the projectile and of the other as the target. Trans- 

 mutation does not occur whenever a projectile comes into the neigh- 

 borhood of a target nucleus, but only on rare occasions which I will 

 call "lucky hits." There are four principal kinds of projectiles in 

 use for transmutation : Helium nuclei — hydrogen nuclei of two sorts, 

 the light and the hea\^ — and neutrons. Three stages of my chro- 

 nology have been marked with their names. The phenomena of fission 



» DeHvered before the National Academy of Sciences at Its Washington meeting, April 28, 

 1940. Reprinted by permission from Science, n. s., vol. 91, May 31, 1940. 



155 



