86 SCIENCE REMAKING THE WORLD 



respond to the reduced attraction of the nucleus. The 

 result is the formation of an atom of an entirely different 

 chemical element with different chemical properties. 



This process has continued for ages, gradually de- 

 creasing the supply of uranium. In its place are its 

 disintegration products, uranium X, so-called, and 

 helium because the emitted alpha particle soon finds 

 two electrons to act as its planets and with them settles 

 down to the uncompanionable existence of a helium 

 atom. 



The expulsion of an alpha particle from a uranium 

 atom fails, however, to cure its internal troubles. Two 

 electrons are therefore successively expelled from the 

 nucleus of the newly formed uranium X,. The excess 

 of protons in the nucleus is increased from ninety to 

 ninety-one and then to ninety-two. The expelled 

 electrons shoot into space with enormous velocity, but 

 their independent careers are not our present concern. 



With their leaving, the nucleus returns to a condition 

 of ninety-two excess protons. Thereafter it is a spend- 

 thrift, losing one alpha particle after another until it 

 finally becomes identical with the nucleus of the lead 

 atom, which has an excess of eighty-two. During its 

 downward progress it serves for a time as the nucleus 

 of the well-advertised radium atom. 



The radioactive elements are responsible for much 

 of our present-day knowledge of electronic physics. 

 They gave away the inner secrets of a large group of 

 atoms to such ingenious and persistent investigators as 

 Professors Rutherford and Soddy. It was the former, 

 for example, who proved that the alpha particle is really 



