Contemporary Advances in Physics, XXVII 

 The Nucleus, Second Part * 



By KARL K. DARROW 



In this Second Part the major subject is Transmutation: that is to say, 

 the alteration or disintegration of a nucleus, the unique and distinctive part 

 of any atom, by impacts of fast-moving corpuscles. For the last year and 

 a half the pace of progress in this field has been increasingly rapid, and in all 

 likelihood is destined to become yet swifter. This is partly because of the 

 discovery — a discovery due largely to theoretical foresight — that trans- 

 mutation of some elements is practicable with protons of a relatively 

 modest energy which can be produced in laboratories without any serious 

 difficulty. Partly it is due to the discovery of neutrons and of deutons, 

 particles which apparently possess remarkable ability in effecting certain 

 kinds of transmutation. Partly also it is due to advances and refinements 

 in the methods of working with alpha-particles, the first variety of corpuscle 

 with which disintegration of nuclei was ever achieved. People are already 

 beginning to speak of "nuclear chemistry" as a special branch of science, 

 and this is already almost justified by the number of cases known in which 

 two nuclei interact and produce two others which are recognizable. 



Bringing the First Part up to Date 



STRANGE as it seems to speak of "bringing up to date" something 

 that was pubUshed only six months ago, one is sometimes obHged 

 to do so by the rapid march of science; and three of the "elementary 

 particles" of which I spoke in the First Part were and still are so 

 young— or to speak more carefully, our acquaintance with them is 

 still so young — that their role and situation in the body of physical 

 knowledge is changing from month to month. 



The Positive Electron 

 Of the positive electron the most striking new thing to be said is, 

 that there is now a new way of generating it: by impacts of alpha- 

 particles against metals. This so far has been applied only by its 

 discoverers, M. and Mme. Joliot; only with alpha-particles from 

 polonium, therefore of energy 5.3 millions of electron-volts; only to 

 five metals, of which beryllium and boron and aluminium yielded 

 positive electrons, while silver and lithium did not. It is as yet the 

 most efficacious way of producing positive electrons, Joliot having 

 evoked last summer as many as 30,000 of these corpuscles per second 

 from aluminium. This of course looks small when compared with the 

 torrents of negative electrons which incandescent metals will pour out, 



* "The Nucleus, First Part" was published in the July 1933 issue of the Bell Sys. 

 Tech. Jour., Vol. XII. 



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