6G4 Dr. Sadler and Mr. Steven on an Apparent Softening 



It has been shown* that this characteristic radiation is 

 only produced by a more penetrating radiation, and the 

 increase in absorption accompanying its production is a 

 maximum for an exciting beam only slightly more penetrating. 

 In Table VI.* are given the absorption coefficients in different 

 substances o£ the characteristic radiations of the elements 



Cr Ag. From columns II. and III. it will be seen that 



these radiations are in increasing order of penetrating power 

 when tested by elements in which they excite little or no 

 characteristic radiation ; and from column IV. that the 

 absorption coefficient in iron is a maximum for nickel 

 radiation. 



Table VI. 



Mass Absorption 



Coefficients (\ 



Ip). 





Radiator. 



Absorbed. 



C. 



Al. 



Fe. 



Ni. 



Cn. 



143 

 951 

 75-3 

 61-8 

 530 

 55 5 



176 



149-8 

 24-3 



Zn. 



1705 



112 5 



915 



74-4 



60*9 



501 



2035 



174-6 



271 



Cr 



15-3 



10-1 

 7-96 

 6-58 

 522 

 4-26 

 2-49 

 2-04 

 •41 



136-0 

 88-5 

 716 

 59-1 

 47-7 

 39-4 

 22-5 

 18-9 

 2-5 



103 8 

 66-1 

 67'2 



314 



268 



221 



134 



116-3 

 17 4 



129 

 838 

 67-2 

 563 

 62-7 



265 



166 



141-3 

 22-7 



Fe 



Co ... 



Ni 



Cu 



Zn 



As 



i Se 



Ao- 





We should expect that if we placed a sheet of iron in our 

 heterogeneous primary beam, it would specially absorb the 

 constituents of about the penetrating power of nickel radia- 

 tion, and more penetrating constituents to a lesser extent. 

 The portion of the beam too soft to excite iron radiation 

 would be absorbed only to a limited extent. For example, 

 it will be seen that a constituent of the hardness of chromium 

 radiation, of which the absorption coefficient in aluminium is 

 136, would be absorbed to a less extent by iron than that of 

 the radiation from selenium, the absorption coefficient of 

 which in aluminium is only 18*9. On the Avhole, then, the 

 beam after passing through iron would be richer propor- 

 tionately in these softer rays than before, but these latter 

 are much more easily absorbed by aluminium than those 

 specially absorbed by iron, and therefore we would expect 

 the beam to be softer to aluminium after passing through 

 iron than before. 



* Barlda & Sadler, Phil. Mag. May 1909, pp. 739-76 



