ARTIFICIAL TRANSMUTATION 87 



Artificial Transmutation 



The complex nucleus of radium contains 88 protons; therefore, its 

 atomic number is 88. In addition, this nucleus contains 138 neutrons, 

 making a total of 226 entities of atomic weight 226. The neutrons are 

 supposed to play the role of a binding cement which holds the nucleus 

 together in spite of the very strong electrostatic repulsive forces which 

 the positive protons exert upon one another. 



Radium, like many of the natural radioactive types of atomic number 

 greater than 80, does not possess a completely stable nuclear configura- 

 tion. It can, however, become more stable by splitting off a nuclear 

 fragment in the form of an alpha particle. 



Since radioactivity is a quality of the nucleus, it varies from one 

 isotope to another of any element. This nuclear quality of a radioactive 

 atom is the same whether the atom is part of a solid, a liquid, or a gas. 

 It is the same whether the radioactive element is isolated or part of a 

 chemical compound. 



Elements of small atomic number like Li, B, and N have stable nuclei. 

 If, for instance, nitrogen is bombarded with sufficiently high-speed 

 atomic projectiles, it might be possible to dislodge a nuclear proton 

 fragment. The resulting " artificial " nucleus with its complement of 

 planetary electrons would be a " transmuted " element. A transmu- 

 tation may also be brought about by changing the number of neutrons, 

 or by a combination of neutrons and protons in the nucleus. Thus, 

 transmutation is not always a destruction of the nucleus, but frequently 

 a synthesis in which neutrons or protons are added to an original 

 nucleus. 



As early as 1919 Rutherford succeeded in producing the artificial 

 transmutation of an element, although the isotopic elements thus pro- 

 duced were not radioactive. In his first experiments he subjected 

 nitrogen to an intensive bombardment of alpha particles from RaC' to 

 see if he could disintegrate the nucleus of the nitrogen atom. He was 

 successful in breaking down the nucleus, and the products of disintegra- 

 tion were an isotopic atom of oxygen and a nuclear proton. The proton 

 was ejected with a large amount of kinetic energy. 



This classic experiment is shown pictorially in Fig. 11-13. At the 

 time of Rutherford's experiment the constitution of the nucleus was 

 thought to be only protons and negative electrons. They were supposed 

 to be closely and tightly bound together. Disruption of the nucleus 

 was thought to be accomplished by the shooting of a high-speed pro- 

 jectile in the form of an alpha particle at the very small nuclear target. 

 The high-speed alpha particle colliding with the nucleus of the nitrogen 



