1 48 Rontgen Radiation from Substances of Low Atomic Weight. 



It is well known that some substances have more than one 

 type of homogeneous radiation. It is possible that carbon is 

 one of these, though the balance of evidence on the whole 

 makes it improbable that an explanation of the phenomena lies 

 here. The authors incline more to the belief that an actual 

 modification of the X ray occurs in its passage through 

 matter, a general softening taking place. Other evidence 

 favouring this view is accumulating along rather different 

 lines in a separate investigation, the details of which are not 

 yet ripe for publication. One thing appears to be firmly 

 established, viz., the harder the rays, the more profoundly 

 are they modified in their passage through matter. 



An extension of an experiment described in an earlier 

 paragraph seems to bear upon this point. It was pointed 

 out that the radiation from tin consisted of two parts, a soft 

 component having a value for \ in aluminium about 40-50 

 and a hard component for which X is about 4*0. It was also 

 shown that the intensity of the tertiary radiation excited 

 in carbon depended chiefly upon the hard component. On 

 testing the quality of the tertiary radiation, it was found that 

 this too was practically unchanged when the soft component 

 was suppressed. It was found impossible to determine to 

 what extent the tertiary excited by the hard component 

 from tin was heterogeneous, owing to the feebleness of the 

 ionization it produces. The disturbing effects of stray 

 radiations become more pronounced when dealing with a 

 residual ionization. 



No claim for accuracy is put forward with regard to ihe 

 values of X given in column 3, Table III. For if the radia- 

 tion prove to be non-homogeneous it is obvious that they can 

 only represent average values. There can be no doubt, 

 however, that a homogeneous beam is not scattered solely as 

 a homogeneous beam, even if at all. The experiments 

 described do not enable us to determine whether there is a 

 homogeneous radiation emitted by carbon. It is highly 

 probable that such a radiation does exist, though of feeble 

 intensity. 



It is hardly necessary to point out that a clear solution of 

 this problem is bound to have an important bearing on the 

 theory of the production of an X ray. Incidentally, the 

 bearing of these results upon such questions as the polariza- 

 tion and the general distribution of a scattered radiation will 

 need to be carefully considered. 



It is perhaps only fair to mention that, as far as we can 

 judge, the primary heterogeneous beams used in the earlier 

 experiments on scattering were generally of a soft type. 



