RADIOISOTOPES — AEBERSOLD 



225 



Reactor operation is based on the fissioning or splitting of uranium 

 235 atoms in the uranium fuel. Perhaps the only other characteristic 

 necessary for a simple understanding of the reactor as a radioisotope 

 production unit is the neutron flux or density. The flux of the Oak 

 Ridge reactor is of the order of a million million neutrons passing 

 through each square-centimeter area (about the size of a fingernail) 

 per second. 



Radioisotopes are produced in a nuclear reactor either by fission- 

 ing — that is, by splitting of uranium (figs. 3 and 4) — or by bombard- 

 ing ordinary stable elements with neutrons, the subatomic particles 

 that keep the chain reaction going. Although from the standpoint 

 of the physics involved as well as from the standpoint of a manufac- 

 turing process, radioisotope production is a complex operation, in 

 principle it is as simple as putting biscuits in an oven to cook (pi. 2). 

 Almost any element, or for that matter almost any object such as a 

 penny or dime or a bobby pin or the phosphorus from the head of a 

 match, can be placed in a small aluminum tube and introduced into the 



URANIUM FISSION 



AND BETA CHAIN DECAY 



,r /5- Jr 



oioT) r^ M3ic»l r^ (Ruio3) r^ ( Rhio3l 



42p J U^ V 4)p y U-^ V 44p J \^ \ 45p ) 



HALF- llf [-45 CAYS 



MASS 103 FISSION CHAIN 





"RADOIODWE 131- 

 A PIODUCT OF THB CHAIN' 



OMASS 13 1 FISSION CHAIN 



r \ 



HALfLlfE-30 HOURS HAlf-Uft-25MNUTtS HAUift-aCAYS 



Figure 3. — When a fissionable uranium 235 atom is hit by a neutron, it fissions or splits 

 the uranium atom into two different atoms. These atomic fragments are called fission 

 products and make up a wide variety of radioisotopes of elements from zinc, with an 

 atomic number of 30, to gadolinium, with an atomic number of 64. After the uranium 

 slug is removed from the reactor, the fission products are chemically separated from the 

 uranium and plutonium and from each other. One of the most useful radioisotopes 

 produced by this method is radioactive iodine. 



