﻿Problems in Radioactivity. 247 



If we write Ns = Q, and h=--x> in (10), and notice that 



/"(co) = 0, we have 



™V(x*>- 



(12) 



The integral 





/(Xs), 



so that (12) agrees with the result obtained by Eve. 



By means of (10) we may compare the effect of surface 

 lavers of radioactive matter of different depths in their in- 

 fluence on the gradient of intensity of penetrating radiation. 

 If we take the intensity at the surface z = Q as unity, we 

 have to calculate the fraction 



f(\z)-f{\z-Kl) 

 !-/(*/') 



for various values of z and h. It is more convenient, in the 

 use of tables, to calculate the above fraction for various 

 values of \z and k/i. Then, by employing the values of X 

 and k given in Eve's paper, we can find the corresponding- 

 values of z and h. In the following table a few values of 

 the gradient due to layers of different thicknesses are given. 

 The height above the earth's surface (z) is expressed in 

 metres, the thickness of the layer of radioactive matter (A) 

 is expressed in centimetres, and the intensity at the earth's 

 surface is in each case taken as unity. 



Table II. 



, 1 



1 metres. 

 



X, 



h — -\\ cm. 

 Kh= 01. 



h — 1 1 cm. 

 «A=0'1. ■ 



h=\\ cm. 

 jcA=1-0. 



h=ao 

 1000 







1-000 



1-000 



1000 



11-4 



•05 



•472 



•706 



•812 



•828 



22-7 



•1 



•340 



•535 



■696 



•722 



45-5 



•2 



•230 



•370 



•543 



•574 



! 67-2 



•3 



•178 



•288 



•■437 



•469 



I 114 



'5 



•100 



•182 



•207 



•327 



i 159 



•7 



•078 



•123 



-21 -I 



•235 



227 



1-0 



•050 



•07;: 



■13,1 



■148 



