226 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1953 



reactor. After neutron irradiation or bombardment for a week, a 

 month, or perhaps longer, depending on the radioisotope being pro- 

 duced, the aluminum tube is taken out and the radioactive material 

 removed. Depending on the radioisotope produced, it may or may 

 not be chemically processed before shipping it to the user. In some 

 instances the aluminum tube and all are shipped directly to the user 

 after having been placed in the proper shipping container. 



The production output of the reactor is phenomenal. For ex- 

 ample, over 14,000 curies ^ of radioactive cobalt 60 have been shipped 

 from Oak Ridge in the 6 years since the distribution progi\am began. 

 This is comparable to nearly 50 pounds of radium. Although it is 

 difficult to estimate the current world inventory of refined radium, 

 in the 6 years preceding the availability of reactor-produced cobalt 

 60, less than 1 pound of radium was imported by the United States. 



Another example is the case of radioactive carbon 14, one of the most 

 useful radioisotopes for biological tracer studies. It has been esti- 

 mated that 1 millicurie of carbon 14 produced in the cyclotron would 

 cost $1,000,000. The same quantity of reactor-produced carbon 14 can 

 be purchased today for $36. 



RADIOISOTOPE AVAILABILITY 



Of the more than 1,000 nuclear species or isotopes that have been 

 identified to date, some 276 are stable and over 750 are radioactive. 

 Approximately 100 of the radioactive variety are routinely manufac- 

 tured at Oak Ridge and distributed to scientists all over the world. 

 This means that reactor-produced radioisotopes or radioactive forms 

 of most of the known elements are now available in quantities suffi- 

 cient for wide-scale use. Those available include such important 

 radioisotopes as radiohydrogen (tritium, H 3), radiocarbon (C 14), 

 radiophosphorus (P 32), radiosulfur (S 35), radiocalcium (Ca 45), 



* The curie, which gets Its name from Madam Curie, is the unit of radioactivity repre- 

 sented by 1 gram of radium. Today it is defined as the quantity of any radioactive mate- 

 rial giving 37 billion disintegrations per second. 



Figure 4. — One of the principal ways of producing radioisotopes in the nuclear reactor is 

 to bombard ordinary stable isotopes with neutrons, the subatomic particles formed when 

 a uranium 235 atom fissions. The chart shows two types of nuclear reactions which take 

 place when a stable isotope is bombarded with neutrons. In the first case a neutron is 

 absorbed and a gamma ray given off. This has the effect of increasing the atomic weight 

 of the target nucleus by 1, as shown in the production of carbon 14 from carbon 13 and 

 in the production of phosphorus 32 from phosphorus 31. In neither instance is this a par- 

 ticularly good way of producing the radioisotope since there is no way of chemically 

 separating the radioactive isotope from the original stable isotope. The transmutation 

 reaction, on the other hand, results in the production a of radioisotope of a different ele- 

 ment than is used in the original target. Here a chemical separation can be effected and 

 the resultant radioisotope made available in pure form. 



