﻿29G 



Drs. K. Fajans and W. Makower on the 



The Absorption of the /3 Rays of Radium B by Aluminium. 

 The above conclusions respecting RaC 2 depend on the 

 assumption that when working with hard rays the initial 

 activity of a surface coated with RaB is due to the emission 

 of hard ft rays from RaB. As has already been mentioned, 

 such rays have been observed by H. W. Schmidt, but as 

 the correctness of hi* results has been recently called into 

 question by rlahn and Meitner *, it w T as necessary to inves- 

 tigate the matter more fully before any certain conclu- 

 sions could be drawn regarding RaC 2 . For this purpose 

 determinations with an ordinary /3-ray electroscope were 

 made of the rise and subsequent fall of the ionization 

 produced by a plate coated with RaB when measured 

 through different thicknesses of aluminium. Some typical 

 curves showing the results obtained with filters whose 

 thicknesses ranged from to '73 mm. are shown in figure 3. 



Fijr. 3. 



100 



xSO 



40 j* 

















..-_ 







D 

















E^ 

















0> 



*^*~ 















^ 













A 



A 



'Sk 













^ 

















"0246 8 '0 I? 14 16 



Curve A. No aluminium. Carve E. 021 mm. of aluminium. 



B. 0-0140 mm. of aluminium. F. 0*36 „ „ ,. 



C 0-0305 „ „ „ G. 0-73 „ „ 

 D. 0-0446 „ „ „ 



Curves for thicknesses greater than '73 mm. are not given, 



as they differed inappreciably from each other. Thus, 



whereas the curves with the thinner aluminium screens 



* Halm and Meitner. P/ii/s. Zeitschr. x. pp. 097-703 (1909). 



