ATOMIC WEAPONS AGAINST CANCER — LOCKARD 269 



in 1896 to 1941, whereas since atomic energy was developed we have 

 had the equivalent in radioactivity of thousands of tons of it. 



It so happens, fortunately, that not only can the pile produce in 

 great quantity but it can also make all the most important radio- 

 isotopes, including those most helpful in cancer, though the cyclotron 

 still retains important secondary values as a producer. 



The pile can produce a thousand to a million times as great a 

 quantity of isotopes as the cyclotron can ; in contrast to the cyclotron, 

 which uses diiferent types of bombarding particles, even neutrons, the 

 pile is exclusively a neutron machine. It uses neutrons in two ways 

 to manufacture radioactive isotopes. The first way is nuclear fission — 

 the actual splitting of nuclei. Each nucleus of the target element, 

 uranium, that is hit by one of the bombarding slow neutrons splits 

 (fissions) into two or more fragments, in many different ways; thus 

 many different fission products result. They are radioactive (un- 

 stable), which means that they will give off energy by the emission of 

 one kind of particle or another until they reach a stable isotope or are 

 used up. Strontium 89 is produced in this way and so is iodine 131. 

 But another practical way of producing iodine 131 is by causing non- 

 fissionable nuclei to absorb additional neutrons, and this is the second 

 way of making radioisotopes. 



There are three kinds of neutron absorption — simple absorption, 

 absorption followed by decay into a daughter element, and transmuta- 

 tion. In all three, special target material is inserted into the nuclear 

 reactor, which is already in operation with fission of uranium by 

 neutrons. If, for example, ordinary cobalt (27Co^^) is inserted into 

 the pile, it absorbs one of the neutrons flying about and, while re- 

 maining cobalt (the number of protons and electrons does not change) , 

 becomes cobalt 60, which is radioactive. This is simple neutron ab- 

 sorption. The product realized is always isotopic with the target 

 material. 



In the second kind of neutron absorption, the material put into the 

 reactor to be irradiated is not isotopic with the product wanted in the 

 result, but a different element. A practical method of producing 

 radioiodine comes here. A stable isotope of tellurium (,:;Te"°) 

 is inserted into the reactor; when it absorbs a neutron it becomes 

 BaTe^^^ which, being unstable, decays by emitting a beta ray; the 

 emission of the beta ray involves first the conversion of a neutron 

 into a proton and an electron and second the ejection of the electron 

 (beta ray and electron mean the same thing) with the proton staying 

 in the nucleus ; thus the atomic number changes from r)2 to 53 (since 

 there is a gain of the proton) and the atomic weight stays the same 

 (since the loss of the neutron is balanced by the gain of the proton; 

 and so B2Te^^^ by beta decay becomes ssI^S a daughter element. 



