7 Rays from the Uranium Products. 



253 



a very thin layer o£ material. The purity of the uranium X 

 used was tested by measuring its rate of decay. 



As the apparatus and method used in the experiments 

 were the same as those previously employed *, it is not 

 necessary to give details. It may be pointed out, however, 

 that, as the amount o£ uranium X in equilibrium with one 

 kilogram of uranium nitrate corresponds in 7 ray activity 

 to only about '01 mgrm. of radium, the activities obtained 

 were very small and consequently the absorption coefficients 

 could not be measured with great accuracy. 



The absorption curves, using aluminium as the absorbing 

 substance, were obtained and analysed in the usual manner. 



riff. 1. 



90 



70 



^50 



I 



30 



1 y\ 













14 w 



= 24 











1-2 

























1-0 









— 



•8 













•8 1-2 1-6 



TH/CHNESS Of ZlLUMtNIUM /N MMS. 



2-0 



2-4 



Fig. 1 shows the initial portion of the curve. It will be 

 seen from the figure that about 40 per cent, of the total 

 radiation is absorbed by 2 mm. of aluminium. The absorp- 

 tion, as shown by the logarithm curve, is exponential, the 

 absorption coefficient //, in aluminium being 24 (cm.) -1 . 



The determination of the absorption curve for greater 

 thicknesses of aluminium was a matter of some difficulty 

 owing to the very small activity (0'3 div. mill, initially) at 

 my disposal. It was for this reason impossible to obtain the 



* Rutherford and Richardson, Phil. Mag. xxvi. p. 324 (1913). 



