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LXV. Scattering and Absorption of Hard X-Rays in the 

 Lightest Elements. By Tycho E:SON Auren, Ur.phil* 



BY the aid of a compensation metliod in adjusting the 

 thickness of a water layer so that its absorption for a 

 pencil of X-rays is equal to that of a liquid layer of the 

 thickness of 1 cm. or of a sheet of metal of known thickness, 

 I have made determinations of the relative atomic absorption 

 coefficients of a number of elements, and 'I have given an 

 account of the results of these researches in a previous paper "f. 

 Barkla and other authors have shown that, for many elements 

 and at different wave-lengths, the relation of the absorption 

 coefficients is independent of the wave-length. In calcu- 

 lating the coefficients, I have assumed that such was the case 

 for all elements. As the influence of the effect of scattering 

 in the lightest elements is so great compared with true 

 absorption that it cannot be neglected, it was supposed that 

 the deviations from the constant relation of the absorption 

 coefficients in different wave-lengths was entirely due to this 

 effect. By means of the determination of the absorption 

 in H, which may be considered, with no appreciable error, to 

 be exclusively dependent on scattering, a measure of the 

 scattering effect caused by one electron was obtained, and 

 aided by this measure I then tried to state the number of 

 electrons, i. e. outer electrons, which in different elements 

 produce scattering. 



As far as I know, there has not yet been performed any 

 investigation into the question whether the relation of the 

 values of absorption coefficients of the lightest elements 

 corrected for scattering is constant, which lacuna has 

 certainly been left owing to the difficulty there is in deter- 

 mining accurately the extent of the scattering effect. My 

 estimation just mentioned of the number of the outer 

 electrons being essentially dependent on the determination 

 of absorption in the lightest elements, I have found it 

 necessary, in recent experiments, to try to determine more 

 accurate values of the magnitude of absorption in these 

 elements. Particularly it has appeared of importance to me 

 to bring about more accurate measures regarding absorption 

 • of hydrogen. The method of research has been identical 

 with that used earlier, with the exception of using a Coolidge 

 bulb and considerably shorter wave-lengths than before. 



* From the Meddelanden /ran K. Vetenskapsakademiens Xobeh'us/itut, 

 JBd. iv. No. 5. Communicated by the Author. 



t Medd. fr. K Vet.-Akad. Nohelinstitut, Bd. iv. No. 3 (1919), ami 

 Phil. Mag. xxxvii. p. 165 (1919). 



Phil.' Mag. S. 6. Vol. 41, No. 215. May 192L 3 C 



