220 ANNUAL REPORT SMITHSONIAN INSTITUTION, 195 3 



scholars as Kelvin, Helmholtz, Boltzman, Michelson, and Lorentz that 

 all the great discoveries in physics had already been made and that 

 future progress was to be looked for, not in bringing to light qualita- 

 tively new phenomena, but rather in making more exact quantitative 

 measurements upon old phenomena. In simpler terms this meant ob- 

 taining more significant figures beyond the decimal point. As Robert 

 Millikan said after hearing Professor Roentgen report his discovery 

 of X-rays to the German Physical Society, ". . . we all began to see 

 that the nineteenth century physicists had taken themselves a little 

 too seriously, that we had not come quite as near sounding the depths 

 of the universe, even in the matter of fundamental physical principles, 

 as we thought we had." But no one, even as recently as 25 years ago, 

 dreamed of the amazing developments of nuclear physics or atomic 

 energy that have taken place since. 



Radioactivity was the key that had opened up door after door in 

 the dramatic development of nuclear science. It was the study and 

 use of radioactivity that led to Rutherford's concept of the atom, to 

 Soddy's concept of isotopes, to Chadwick's discovery of the neutron, 

 to the Joliot-Curie's man-made radioactivity, and finally to Hahn's 

 discovery of fission from which have come both the chain reaction 

 and the nuclear reactor. 



ISOTOPES 



But radioactivity proved more than an ordinary key. It has been 

 a master key, for it has provided us with a whole chain of "new keys." 

 We shall concern ourselves here with only one of these "keys" — the 

 reactor-produced radioactive isotopes. We shall consider the pro- 

 duction, distribution, and use of these radioisotopes and look at what 

 radioisotopes have meant to science and what they may mean to the 

 individual. 



At the risk of going backward once more, let us try to imagine what 

 scientific tool investigatoi-s of 25 years ago might have desired most. 

 I am thinking now not only of physicists but also of chemists, biolo- 

 gists, physiologists, and other types of researchers. Among the things 

 that scientists of that day could not do but no doubt sincerely wished 

 they could do was "to trace atoms." Think of being able to trace a 

 certain diet element or compound through the digestive and metabolic 

 processes of an animal or even a human being. Think of being able 

 to find out what plants do with carbon dioxide or with fertilizer, or 

 following the diffusion of atoms in solid metal. Scientists of 25 

 years ago could only dream of doing these things. Man-made radio- 

 isotopes have now made these dreams possible! Today, even un- 

 dreamed of things have become routine. But the story taken from 

 this page of science is much more dramatic than "first you can't, then 

 you can." 



