270 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1951 



In the third kind of neutron absorption, called neutron transmuta- 

 tion, again a target element nonisotopic to the radioactive element 

 desired is inserted into the operating reactor. A good example is 

 carbon 14, which is produced in practical quantities by neutron trans- 

 mutation. Ordinary nitrogen (7N") is the target material; absorbing 

 a neutron, it emits a proton ; the loss of the proton drops the atomic 

 number one place and therefore changes the element ; the gain of the 

 neutron keeps the atomic weight the same; thus 7N" is transmuted 

 into sC^*. Similar transmutations are possible with the emission of 

 alpha j)articles instead of protons. 



This is not the whole story of the production of radioisotopes in 

 the nuclear reactor by means of neutron bombardment. How the 

 radioisotope desired is separated from the other fission products or 

 from stable isotopes is also, to name one aspect, a part of the complete 

 story. Additional points to remember, however, are that any com- 

 mon element can be irradiated in the reactor, that what radioisotopes 

 the reactor cannot make the cyclotron can, and that between them they 

 account for more than 500 induced radioactivities — every one of the 

 96 elements has at least one known radioisotope. One point more 

 and an important one for cancer research is that both the cyclotron 

 and the reactor, because they use different means and therefore accom- 

 plish different ends, are needed in the constant experiments being 

 carried on for new isotopes and for isotopes of varying specific activi- 

 ties, half-lives, and energies. 



The facilities which need to be brought together in order to provide 

 maximum effectiveness in cancer research are varied indeed. In the 

 research center itself many kinds of experts are needed — radiological 

 physicists, biologists, and medical experts who know the effect of 

 radioactivity on living things and how to safeguard health ; chemists 

 who can separate cancer-useful products from the other products of 

 the reactors and can sj^nthesize radioactive chemicals and drugs into 

 chemically useful compounds; and experimental nuclear physicists 

 who can select materials for insertion into the reactors. The equip- 

 ment for producing radioisotopes should also be near at hand, so that 

 the laboratories will receive quickly those radioisotopes that are so 

 short-lived that transportation over a distance is impractical. Such 

 equipment must, of course, include a cyclotron, for the sake of its 

 distinctive products, and a nuclear reactor or pile. 



Here the Atomic Energy Commission is vitally involved, for the 

 pile is primarily a producer of fissionable materials, and in the words 

 of the Atomic Energy Act, "all right, title, and interest within or 

 under the jurisdiction of the United States, in or to any fissionable 

 material, now or hereafter produced, shall be the property of the 

 Commission" and "the Commission * * * shall be the exclusive 



