Radioactivity of Lead and other Metals. 



763 



This cylinder was treated precisely the same as the others, 

 but on account of its high activity special measurements were 

 made with it in order to investigate more fully the character 

 of the radiation which it emitted. 



Measurements on the radiation from this cylinder showed 

 it to be in great measure an easily absorbed one. When 

 aluminium linings 0'73 mm. thick were inserted in cylinders 

 No. 1, No. 2, and No. 3, and measurements made on their 

 saturation currents, the values of "g" were found to be 

 12*0, 13*3, and 14*4 respectively. These numbers, it will be 

 seen, are slightly lower than those found for aluminium 

 alone, which is exactly as one would expect owing to the 

 absorption of the penetrating rays from the earth by the lead. 

 The value for " q " 13*3 found for No. 2 is slightly greater 

 than that "q" = 12 given by No. 1, although this lead 

 cylinder was 2*25 mm. thick, while No. 1 was only 1*85. 

 This would seem to indicate the existence of a penetrating- 

 type of radiation issuing from No. 2 which was absent from 

 cylinder No. 1. 



A second series of measurements was made with cylinder 

 No. 2 to investigate the distribution of the substance which 

 was the cause of its high activity. Readings were taken on 

 the saturation current first with the lead cylinder entirely 

 unscreened, then with one half of the cylindrical surface 

 screened internally with aluminium 0*73 mm. thick, and 

 finally with the whole of the inner cylindrical surface covered 

 with the aluminium. 



The values are given in Table II., and from them it will 



Table II. 



Experiment 

 number. 



Cylinder No. 2. 



Ionization. 



(Arbitrary 

 Scale.) 



Decrease in 

 Ionization. 

 (Arbitrary 



Scale.) 



1 



Completely un- 

 screened. 



One-half inner 

 cylindrical sur- 

 face screened. 



All inner cylin- 

 drical surface 

 screened. 



546 



J 22-2 

 22-57 



9 



324 



3 



9-87 





be seen that the decrease in conductivity was the same for 

 each half of the cylindrical surface. This goes to show 

 that the radioactive impurity in the lead was uniformly 



