Radioisotopes — New Keys to Knowledge^ 



By Paul C. Aebersold 



Director, Isotopes Division, U. S. Atomic Energy Commission 

 Oak Ridge, Tenn. 



I With 4 plates] 

 CHRONOLOGY 



Twenty-five years ago the field of atomic energy as we know it today 

 had not even been conceived ; nuclear science was just getting under 

 way. Of course, Koentgen had discovered X-rays; Becquerel had 

 discovered radioactivity; the Curies had discovered radium and 

 polonium; Rutherford had originated his concept of the atom with a 

 tiny, heavy nucleus surrounded by planetary electrons; and Soddy 

 had proved the existence of isotopes— different forms of atoms of the 

 same element— and some 30 different naturally occurring radioactive 

 isotopes had been identified. The fact that atoms of an ordinary 

 stable element may differ in weight, that elements may have stable 

 isotopes, had been determined from positive ray studies by J. J. 

 Thompson and Aston. Also, Rutherford, working with alpha par- 

 ticles from radioactive sources, had observed the transmutation of 

 nitrogen atoms to oxygen atoms. 



In spite of the seemingly large volume of information that had been 

 accumulated by 1928 on the atom and its nucleus, the real attack on 

 the nucleus itself and an understanding of what it is made of was yet 

 to come. Chadwick had not discovered the neutron; Anderson had 

 not discovered the positron ; Urey had not discovered deuterium ; I. 

 Joliot-Curie and her husband, F. Joliot, had not discovered that radio- 

 activity could be induced in ordinary stable elements; E. O. Lawrence, 

 of the University of California, had not invented the cyclotron; and 

 nuclear fission and the uranium chain reactor were entirely beyond the 

 realm of imagination of our most learned physicists. 



Roentgen's discovery of X-rays and Becquerel's discovery of radio- 

 activity just before the turn of the century had begun the era of modern 

 physics. It was generally agreed by such learned nineteenth-century 



1 Twenty-sixth Annual Faraday Lecture, Pasadena City College, Pasadena Calif Feb- 

 ruary 19, 1953. 



219 



