X 



9 



•409 



s 



7 



•2 



s 



Energy scattered. 

 " Total energy absorbed. 



•5 



2-5 



•2 





•08 



24-3 



•4 





•016 



the Absorption of Rontgen Rays. 755 



, t n ,, „ energy scattered » 



approximate values for the fraction — -, -, — r tor 



energy absorbed 



the most penetrating and the most absorbable beams used in 



these experiments. . '' 



I. Moderately penetrating radiation (from Ag) : — 



Absorbing 

 Substance. 



c . . , 



Al . . 



Cu . . , 



Ag . . . 13-3 1-5? -11 



II. Yery soft radiation (from Cr) : — 



C . . . 15-3 '2 -013 



Al . . . 135 -2 -0015 



Cu . . . 143 -4? -003 



Ag . . . 580-5 1*5 -0026 



It has been shown in a previous paper * that the energy 

 of the secondary radiation characteristic of an absorbing- 

 element is in many cases probably very great. In a certain 

 case the ionization produced by these rays from Cu was about 

 300 times that produced by the scattered rays from an equal 

 mass of light elements. If we assume as an approximation 

 that the absorptions of two different beams in air are pro- 

 portional to the ionizations produced in air, we are led to the 

 conclusion that in this case the energy of the homogeneous 

 radiation was 45 times the energy of scattered radiation and 

 about ^ of the total absorption, or more than J of the special 

 absorption connected with the emission of these homogeneous 

 rays. 



It was also shown in the paper referred to that the 

 secondary radiation excited in one of these substances (Cu) 

 was proportional to the ionization produced by the primary 

 beam in a thin film of air — or proportional to what may be 

 called the coefficient of ionization in that substance — when 

 the primary was beyond a certain penetrating power. 



We may thus express this : — 



x^'Cu * x l air > 



but, on the assumption stated, 



x\iv ^Air' •'• Ahi ^Air- 



* Barkla and Sadler, Phil. Mag. Oct. 1908, pp. 550-584. 

 3E 3 



