ABSORPTION OF BETA RAYS 



69 



emission, as shown above, is not a homogeneous velocity group. If the 

 electronic emission were, for simplicity's sake, confined to a narrow 

 cylindrical pencil and were allowed to impinge normally on a metal 

 filter, the electrons would be subject to so much scattering in their pas- 

 sage through the metal that some of them would be found to be re- 

 emitted on the incident side of the filter. Even under these simplified 

 conditions it would be found that an original parallel beam had become 

 diffused very rapidly. 



TABLE II-5 

 Relative Amounts of Radiation Transmitted by Various Metal Filters 



By Courtesy of E. H. Quimby, Memorial Hospital, New York. 



The absorption laws governing the loss of electrons, possessing random 

 velocities, as they pass through matter are very complicated. For all 

 practical therapeutic purposes the electrons which pass through a filter- 

 ing metal can be considered as suffering an exponential reduction in 

 number. 



