436 Mr. H. F. Biggs on Energy of Secondary Beta Rays 



Fig. 4 gives a typical pair of curves obtained by this 

 method. 



Fig. 4. 

 fO, — — i 1 1 ii-0 



•58 1-16 1-74- 



Thickness, of screen over source. 



2-32cm.Pb. 



As before, curve R is for the radiator in place, curve X 

 for the radiator removed. Curve L is obtained by plotting 

 the logarithm of the difference of curves It and X. It is 

 seen that the exponential law holds for thicknesses above 

 0'2 cm. of lead. 



Fig. 4 shows the results for varying A7, the screen over 

 the source, when A/3, the screen over the electroscope, is kept 

 at *47 mm. of aluminium. Similar results were obtained for 

 A/3 = *25 mm. and A/S^^mm. aluminium. 



The following" table — 



A/3, 

 mm. Al. 



Limits of x, 

 cm. Pb. 



cm.— 1 



•25 



•47 



•86 



•6, 2-3 

 •3, 1-2 

 •4, 1-2 



•64 



■m 



•67 



