Rontyen Radiation and Corpuscular Radiation. 



453 



The values of /3 2 , the absorption coefficient of the cor- 

 puscular radiation in air, were given in a previous paper. 

 The absorption coefficients of the corpuscular radiation in 

 the material of the tertiary radiators were not measured 

 directly. It is known that for soft /3 rays the absorption in 

 different substances approximately obeys a density law. The 

 corpuscles here dealt with correspond to very soft j3 rays, 

 and may be expected to suffer absorption in a similar manner. 

 But whatever law the absorption obeyed, it is probable that 

 the ratio of the absorption coefficients in air of the corpuscular 

 radiation excited by any two secondary X radiations is equal 

 to the ratio of these absorption coefficients in a metal. 

 Referring to the expression for k it will be seen that if fii is 

 large compared with X x (which in practice proves to be the 

 case), then since we are chiefly concerned with the relative 

 values of k for a particular tertiary radiator a knowledge of 

 the actual values of fti is not of great importance. 



The values of the various absorption coefficients required 

 in the above calculations are given in the following table. 



Table II. 



Secondary 

 Radiator. 



Values of 

 A x . Al as 

 Absorber*. 



Values of 

 (3 2 (meant.) 



Values of X 3 . 



Fe as Absorber. 



Cu as Absorber. 



Iron 



239 

 193-2 

 159-5 

 128-9 

 106-3 

 607 

 51-0 

 25-5 

 131 

 8-44 

 675 

 4-33 



38-9 

 370 

 35-8 

 301 

 26-4 

 20-8 

 15-3 

 10-7 

 8-83 

 G-56 



514 



521 

 2440 

 2080 

 1715 

 1040 



903 



444 



278 



140 

 99 2 



851 

 674 

 554 

 474 



497 



1575 



1340 



681 



417 



19S 

 145 



Cobalt 



' Nickel 



, Copper 



Zinc ! 





Selenium 





Molybdenum 



Rhodium '■ 



Silver . 



Tin 



1 



* The values of X„ and X 4 are obtained from the corresponding values of X x 

 by multiplying by the factor '0000875. 



f The values of /3 1 , the absorption coefficient of the corpuscular radiation in 

 the material of the tertiary radiator, are obtained by multiplying the value of 

 ,&,, the absorption cofficient of the corpuscular radiation in air, by the factor 



— ■ . where p x is the density of the material of the tertiary radiator and p 2 the 



density of air at 76 cm. of Hg and 0° C. 



Phil. Mag. S. 6. Vol. 22. No. 129. Sept. 1911. 2 H 



