Secondary y Radiation, 



23" 



experiments of the writer when the side of the electroscope 

 was three millimetres of lead. When very penetrating 

 X rays are allowed to impinge on carbon, Pealing* has 

 shown that carbon acts in an anomalous manner. 



Similar curves were obtained when the emanation was 

 surrounded by a screen of lead *084 cm. thick. 



In fioure 8 are given the ionization currents when the 

 lead radiator was increased in thickness from O'Ol cm. to 

 about 0*38 cm., and when the aluminium radiator was in- 

 creased from 0*161 cm. to 0'96 cm. The experimental arrange- 

 ment was similar to that shown in fig. 3. It is clearly seen 

 that lead produces more " returned " radiation than does an 

 equal mass of aluminium. 



Fiff. 8. 













ALUM/, 



/ 



<V/UM ' 





























^ IE/JO 















































M/tSS PEft UN/T AREA 



The returned radiation when the lead radiators are increased in thickness 

 from 0-01 cm. to 0*38 cm., and the aluminium radiators are increased 

 from 0-161 cm. to 096 cm. 



Varying the side of the Electroscope. 



In the above experiments the side of the electroscope was 

 always aluminium. It was thought that the side of the 

 electroscope through which the rays enter might exercise a 

 definite influence over the apparent distribution of the 

 secondary radiation. It is well known that the relative 

 amount o£ /9 rays produced in different materials is dependent 

 * Pealing, Phil. Mag. Nov. 1912. 



