132 



Mr. M. Ishino on the Scattering and 



Rice expressly point out that their equation connecting 

 wave-length and absorption cannot be extrapolated for lead 

 beyond the wave-lengths examined by them. It is obvious 

 that this is the case not only for lead but for other elements, 

 since the values of \\p found in this present paper for 

 aluminium and lead, viz. *071 and *076 respectively, in 

 the case of the penetrating gamma rays, are considerably 

 less than the value of 012 taken by Hull and Rice for 

 the scattering coefficient alone. Such results indicate that 

 the scattering coefficient decreases in value for high fre- 

 quencies, and that the formulse given by Hull and] 1 Rice 

 cannot be extrapolated. 



§ 2. Principle of the Method for the Determination \oj the 

 Scattering Coefficient and the True Absorption Co- 

 efficient. 



Suppose a very narrow beam SA of homogeneous gamma 

 rays penetrates a plate R x normal to its surface (fig. 1). 



Fig- 1. 



The intensity I of the beam at a point P in the plate 

 distant x from the incident surface is, by (1), 



1 = 1 



o* 



•(ft+&)x 



The primary beam is scattered in all directions under some 

 law of distribution. Let us denote this law by f(0), where 

 6 is the angle measured from the direction of the primary 

 beam. Then the amount of scattered rays proceeding 

 from P in a hollow cone of semi-angle and thickness d9 



is 



I o e-^+^ x <Tf(0)e-^+W-^ sece 27r sin 6 . dO . dm. 



