92 



RADIOISOTOPES IN BIOLOGY AND AGRICULTURE 



which by calculation should be adequate, instrumental measurements 

 should always be made as an added guarantee. Morgan (42) has pub- 

 lished a very useful bulletin on the practical problems of shielding. 



Beta-ray shielding is a relatively simple matter. The data from Fig. 

 3-1 may be used to estimate the thickness of shielding to stop completely 

 beta rays of the maximum energy being used. In the case of large 



11 



10 



17 



^6 



o 



E 



c 



12 3 4 



Energy, E Mev 



Fig. 3-1. Thickness, in millimeters, of typical materials required to stop completely 

 beta rays of maximum energy E, in millions of electron volts. {From "Safe Handling 

 of Radioactive Isotopes," Natl. Bur. Standards Handbook 42, September, 1949.) 



sources, however, attention must be given to the occurrence of brems- 

 strahlung. As will be noted, the thickness of glass in the usual bottle or 

 container will often provide adequate shielding. It must be remembered 

 that, although there may be no radiation through the walls of an open 

 beaker or bottle, the area above the open top might be quite hazardous. 

 Gamma-ray shielding is somewhat more complicated, but the require- 

 ments may be readily estimated with adequate precision by certain 

 approximate relationships, namely, (a) the roentgens produced per 

 amount of radioactivity, (6) the reduction of intensity in terms of half- 



