[KING] ABSORPTION PROBLEMS IN RADIOACTIVITY 105 
the slab. This will be negligible if the radius abelarge compared with 
h, and P be not too close to the plate. 
If we have a screen of absorbing matter thickness b, co-efficient 
of absorption mw interposed between P and the circular plate, the 
intensity at P is given by the formula— 
n= ET ju + Az) — f(ub + Az + he) — cores (2+) 
ne ee _~* =) Hy eee (14) 
~ 
Fie: 5. 
We may perhaps notice that the screening effect of the slab (b,x) is 
independent of its position between P and the active slab, as far as the 
primary rays are concerned. Formula (14) is of considerable generality 
and includes all the results already given. 
