the Absorption of Rontgen Rays. 759 



Summary. 



By the use o£ homogeneous beams o£ X-rays varying 

 considerably in penetrating power the laws governing the 

 absorption o£ X-rays have been investigated. The results of 

 experiments may be briefly stated as follows : — 



For very absorbable radiations the ratio between the 

 coefficients o£ absorption in any two elements remains 

 approximately constant while the penetrating power o£ the 

 radiation varies greatly. 



This law, however, does not hold when the radiation 

 transmitted through an element is made more penetrating 

 than the secondary radiation characteristic o£ that element; 

 this, again, is the condition necessary to the production o£ 

 that secondary radiation. 



As the primary radiation is made more penetrating than 

 this secondary radiation, the absorption in this particular 

 element increases, first slowly, then very rapidly. The 

 secondary radiation — homogeneous and characteristic o£ 

 the element — begins to be emitted, first feebly, then in con- 

 siderable intensity. The absorption increases to many times 

 the absorption experienced by a somewhat " softer " 

 radiation. 



When the primary radiation is made still more penetrating, 

 the absorption again begins to decrease and the intensity of 

 secondary radiation decreases at the same rate as the ioniza- 

 tion produced by the primary radiation in a thin film o£ air. 



In the case o£ the transmission of a penetrating radiation 

 through elements of low atomic weight, the energy o£ the 

 primary beam which appears as secondary radiation of the 

 same penetrating power as that of the primary producing it 

 — scattered radiation — is a considerable fraction of the total 

 energy absorbed. 



In other cases investigated the fraction is small. 



Evidence points to the conclusion that in the case of trans- 

 mission of primary rays which are most efficient as producers 

 of the secondary rays in any element, the energy of this 

 secondary radiation is a considerable fraction of the energy 

 absorbed. 



Investigation has failed to reveal any transformation of X- 

 rays by transmission, other than the transformation into secon- 

 dary rays proceeding in all directions. The laws discovered 

 are sufficient to account for a great variety of apparently 

 complicated results recorded by many investigators. The 

 authors are not aware of any peculiar phenomenon of absorp- 

 tion which cannot be explained in terms of these laws. 



