TRANSMUTATION" OF MATTER — RUTHERFORD 205 



with a-particles. The amount of radium available in our laboratories 

 is, however, limited, and it was early recognized that if our knowledge 

 of transmutation was to be extended, it was necessary to have a copious 

 supply of fast particles of all lands for bombarding purposes. It is 

 well known that enormous numbers of protons and deuterons, for 

 example, can be easily produced by the passage of the electric dis- 

 charge through hydrogen and deuterium (heavy hydrogen). To be 

 effective for transmutation purposes, however, these charged particles 

 must be given a high speed by accelerating them in a strong electric 

 field. This has involved the use of apparatus on an engineering scale 

 to provide voltages as high as 1 million volts or more, and the use of 

 fast pumps to maintain a good vacuum. 



A large amount of difficult technical work has been necessary to 

 produce such high D. C. voltages and to find the best methods of apply- 

 ing them to the accelerating system. In Cambridge, these high 

 voltages are produced by multiplying the voltage of a transformer 

 by a system of condensers and rectifiers; in the United States of 

 America by the use of a novel type of electrostatic generator, first 

 developed by Van der Graaf . Professor Lawrence, of the University 

 of California, has devised an ingenious instrument called a "cyclotron" 

 in which the charged particles are automatically accelerated in 

 multiple stages. This involves the use of huge electromagnets and 

 very powerful electric oscillators. By this method he has succeeded 

 in producing streams of fast particles which have energies as high as 

 the a-particle ejected from radioactive substances. Undoubtedly this 

 type of apparatus will prove of great importance in giving us a supply 

 of much faster particles than we can hope to produce by the more 

 direct methods. 



It was at first thought that very high potentials of the order of 

 several million volts would be required to obtain particles to study 

 the transmutation of elements. Here, however, the development of 

 the theory of wave-mechanics came to the aid of the experimenter, 

 for Gamow showed that there was a small chance that comparatively 

 slow bombarding particles might enter a nucleus. This theoretical 

 conclusion has been completely verified by experiment. In the case 

 of a light element like lithium, transformation effects can be readily 

 observed with protons of energy as low as 20,000 volts. Of course, 

 the amount of transformation increases rapidly with rise of voltage. 



The study of the transmutation of elements by using accelerated 

 protons and deuterons as bombarding particles has given us a wealth 

 of new information. The capture of the proton or deuteron by a 

 nucleus leads in many cases to types of transmutation of unusual 

 interest. For example, the bombardment of the isotope of lithium of 

 mass 7 by protons leads to the formation of a beryllium nucleus of 

 mass 8 with a great excess of energy. This immediately breaks up 



