268 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1951 



organs have shown sufficient concentrating power to make radioactive 

 hormones look promising. 



Where does medical science get these radioisotopes on which it 

 increasingly relies? The first source was the cyclotron, or atom- 

 smashing machine, but this source has now been reduced to a very 

 minor position by the nuclear reactor, or pile. In certain very limited 

 respects, the cyclotron can do things which the pile cannot do. It can 

 use different types of bombarding particles, and because of this 

 variety in projectiles and diversity in energy, it can make some radio- 

 isotopes that the pile cannot (sodium 22 and arsenic 74 are examples), 

 and it can also produce a few radioisotopes better than the pile can 

 produce them — radioisotopes with a higher specific activity, which 

 is the ratio of the radioactive atoms to the stable isotopic atoms with 

 which they are mixed, and carrier- free radioisotopes (isolated from 

 the stable isotopes). But some of its products are inferior to those 

 of the pile. For instance, where the pile produces iodine 131 with a 

 half-life of 8 days, the c3''clotron produced iodine 130 with a half -life 

 of only 12 hours. In terms of research this meant that unless the 

 research laboratory was near the cyclotron, the iodine 130 would have 

 radiated away by the time it arrived. But this deficiency was negli- 

 gible as compared with the one great drawback of the cyclotron — its 

 limited capacity for production. Atom-smashing cyclotrons have 

 always been few and far between, and their products few and expen- 

 sive. A great deal of research which was being planned by medical 

 and biological men throughout the country had to be held up until 

 something came along that could produce the desired isotopes in 

 sufficient abundance to make them cheap enough to buy and available 

 to all who could use them. 



On December 2, 1942, this something appeared when the first self- 

 sustaining chain reaction was achieved at the University of Chicago 

 and nuclear fission became a reality. Nuclear reactors were built, of 

 course, not to produce isotopes, but to provide fissionable material 

 for the atom bomb and related research. For a time, therefore, cancer 

 research men could not draw on this potential source of isotopes. 

 But since the end of World War II, the Atomic Energy Commission 

 has moved to make its facilities available and has created for the 

 first time an adequate supply of isotopes. Today, 70 percent of the 

 radioisotope production schedule at Oak Ridge is directed toward the 

 study of cancer, with more than 250 research groups using the prod- 

 ucts. The reason for the excellent production is that the nuclear 

 reactor has proved to be capable of turning out radioisotopes abun- 

 dantly and cheaply. The emphasis is on abundantly ; the cheapness 

 follows from that. The abundance is well illustrated by the fact that 

 only about 1 kilogram of radium had been produced from its discovery 



