RADIOISOTOPES — AEBERSOLD 223 



elements with alpha particles from polonium, discovered quite by 

 accident that ordinary elements can be made to become radioactive. 

 The first man-made radioactive isotope produced was phosphorus 30. 

 It was immediately shown that the path of this new isotope in chem- 

 ical reactions could be followed by its radioactivity. In less than 

 a year Hevesy was using another form of radioactive phosphorus, 

 phosphorus 32, to study the uptake of that element in plants, but only 

 infinitesimally small amounts of radioactive isotopes could be pro- 

 duced in this way. 



CYCLOTRON-PRODUCED RADIOISOTOPES 



Shortly thereafter a new way was found for making larger quan- 

 tities of man-made radioisotopes. E. O. Lawrence and M. S. Living- 

 ston had built their first cyclotron at Berkeley in 1931. It was not 

 long after the discovery of man-made radioactivity that the cyclotron 

 was put to work making radioactive forms of most of the elements. 



Physicists all over the world immediately became engrossed in the 

 possibilities offered by these two developments, the invention of the 

 cyclotron and the discovery of man-made radioactivity. By the start 

 of World War II, 10 years later, radioactive isotopes were being made 

 in perhaps as many as 50 cyclotrons throughout this country as well 

 as in a number of foreign laboratories. By this time the usefulness of 

 radioisotopes for tracing atoms was well established. At least two 

 isotopes, radioactive iodine 131 and radioactive phosphorus 32, had 

 also been used in medicine for the radiation treatment of certain 

 diseases. 



But there was still one catch. Cyclotron production of most radio- 

 isotopes was and still is very slow and very expensive. But most 

 serious of all, the cyclotron can produce only limited quantities of 

 radioisotopes. Therefore, with the exception of those laboratories 

 which were fortunate enough to have cyclotrons, there just were not 

 enough man-made radiomaterials to go around. And even when a 

 cyclotron was available, tracer studies were generally limited to those 

 experiments that would require only a very small amount of the pre- 

 cious radiomaterial. 



REACTOR-PRODUCED RADIOISOTOPES 



The nuclear reactor developed during World War II makes an 

 excellent radioisotope production unit. Although not so wide a vari- 

 ety of radioisotopes can be produced in the reactor as in the cyclotron, 

 what is much more important, the radioisotopes can be produced in 

 large quantity. Also, with the reactor it is possible to produce many 

 different radioisotopes at the same time. This, of course, is not pos- 

 sible with the cyclotron or with other particle accelerators. 



