RADIOISOTOPES — AEBERSOLD 237 



ilarly, radioisotope investigations have helped scientists to understand 

 better the problems concerned with nutrition and diseases of livestock 

 and the production of milk and eggs. 



INDUSTRY 



Like the fields of medicine and agriculture, industry has used radio- 

 isotopes most frequently as tracers in its research and development 

 laboratories. A number of ways, however, have been found for em- 

 ploying radioisotopes as sources of radiation, especially in the control 

 of certain manufacturing operations. 



The simplest type of application depends merely on measuring the 

 change in intensity of radiation from a stationary radioactive source 

 when something is placed between it and the detecting instrument. 

 This change is usually measured by a counter, such as the radioactive 

 thickness gage or liquid-level gage. Sometimes, however, as in radiog- 

 raphy, a photographic film is used as the radiation detector. Instead 

 of an instrument recording we get a photographic picture of the 

 change in radiation intensity. Another type of industrial application 

 depends on using the radioisotope as a movable source of radiation. 

 A source on the end of a flexible rod in tracking an underground 

 sewer line or as an oil marker in an overland pipeline illustrates this 

 type of application. And finally, radioisotopes may be used as tracer 

 atoms to measure the transfer of materials by physical and physical- 

 chemical means and to follow the mechanism of industrial chemical 

 processes. 



Radiographic testing is probably the oldest industrial application 

 of radioactivity and one of the simplest ways of using a radioisotope 

 as a stationary source of radiation. The test is carried out by placing 

 the radioactive source on one side of a weld or casting and a photo- 

 graphic film on the other side. A darkening of the developed film 

 indicates the location of any flaws or cracks since more radiation pene- 

 trates through these places and causes greater exposure to the film. 



Naturally occurring radium and radon used to be the only radio- 

 isotopes available for this kind of application. Today, however, more 

 and more industries are using radioactive cobalt instead ; nearly 200 

 firms have been authorized by the Atomic Energy Commission. 

 Radiocobalt is more readily available and easier to handle than radium. 

 It can also be obtained in greater radiation strength, in any desired 

 shape and size, and is 5 to 40 times cheaper, depending on whether 

 the radium is purchased or rented. 



Another stationary-source type of application is the so-called radio- 

 active thickness gage. In the simplest type of gage a radioactive 

 source which emits beta rays, that is, high-speed electrons, is placed 



