732 Prof. Rutherford and Mr. Richardson : Analysis 



cut out by a thin sheet of lead. The ionization initially fell 

 more rapidly than was to be expected for an exponential law 

 of absorption, but after traversing 1 cm. of lead the absorp- 

 tion of the rays in lead became accurately exponential with 

 a value of /z.= 0"50. 



The absorption of the 7 rays, using the emanation tube as 

 a source, was also determined. In this case, before beginning 

 the measurements, a thickness of lead was used sufficient to 

 absorb completely the 7 rays for which /a = 40 in aluminium. 

 The curve obtained is shown in fig. 6, Curve A. After a 

 thickness of 1*5 cm. of lead the absorption became exponential 

 with a value of /z = 0'50. Since the radiation fi = 0*50 comes 

 entirely from radium C, the curve B (fig. 6) represents the 



Fin;. 6. 



IU0 



90 

 75 

 60 















































\a 













^ 

















k: 

















k 4 45 



















B\ 











• 



30 































15 



















n^C 













■9 VI 



CMS. OF LEAD. 



J -5 



1-8 



ei 



part of the 7 radiation due to radium C alone. The dif- 

 ference curve C given in fig. 6 shows the absorption in lead 

 of the 7 rays from radium B. It is seen that the curve 

 shows a rapid initial drop, which is far more marked than 

 in the case of radium 0. The value of the absorption 



