680 Mr. A. 8. Eve on the Secondary Radiation 
McClelland has shown that the initial values of ) for y rays 
are also variable, so that these rays do not offer a suitable 
test. 
The secondary radiation from a light substance appears to 
be more homogeneous i in character than the primary rays by 
which it is caused (fig. 5). 
In the case of paper screens of thickness 2 the intensity 
of the secondary radiation is proportional to 
eT oe ae ee 
When the primary rays pass through a substance of thick- 
ness a, it will be shown later that the secondary radiation is 
roughly proportional to 
eA -AAAFN) 2s 
And when the secondary rays come from the surface first 
struck by the primary rays, the secondar y radiation is roughly 
proportional to 
1 —e- ata) 
. ow 7 ool ee 
There is a general agreement between the equations and 
the types of curves. 
The radiations due to the rays jointly, and the vy rays alone, 
appear to be similar in character, the latter being less intense 
and of a less penetrating type. The secondary radiations 
caused by Réntgen rays in various substances follow an order 
relative to density different from the secondary radiations 
caused by 8 and y rays jointly, or by y rays alone. The 
penetrating power of the secondary Rontgen rays from 
various substances is also more irregular and in most cases 
more feeble. 
When the primary rays strike the lower surface of a plate 
of thickness a, the intensity in the substance at a distance x 
from the upper surface is now [ye 
Proceeding as above, the total radiation at the upper 
surface will be 
ae 
; —anr —(A+A')z 
kpre ee. 
e 0 
or 
kpr/(X +2) : Gliese: 
A maximum point is given by 
a(X+N)=log.(2N+N)/r. 
The curve in fig. 6 is of a type whose equation is the 
difference of two simple exponentials as above. 
7 
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SE ee 
