Spectrum of the Penetrating y Rays from Radium. 2&% 



The numerical values for the angles of Iceland spar em- 

 ployed in the above calculation are taken from Prof. S. P. 

 Thompson's interesting paper on the Xicol prism read at the 

 Optical Convention of 1905. In conclusion, the writer wishes 

 to express his thanks to Prof. Wilberforce for his kindness 

 in providing the prisms for the experimental tests, and to 

 Mr. J. Proudman, B.Sc, and Mr. J. Foote, who respectively 

 have kindly verified the algebraical and numerical com- 

 putations. 



The George Holt Physics Laboratory, 

 University of Liverpool. 



XXXI. The Spectrum of the Penetrating y Rays from 

 Radium B and Radium C. By Sir Ernest Rutherford, 

 F.R.S., and E. X. da C. Andrade, B.Sc, Ph.D., John 

 Harling Felloiv, University of Manchester*. 



[Plate V.] 



IX a previous paper f, we have given the results of an 

 examination of the wave-lengths of the soft y rays from 

 radium B, for angles of reflexion from rock-salt between 8° 

 and 16°. It was shown that the two strong lines at 10° and 

 12 c correspond to the two characteristic lines always present 

 in the spectra of the " L " series for heavy elements. It was 

 deduced from the experiments ofiMoseley, that the spectrum 

 of radium B corresponded to an element of atomic number 

 or nucleus charge 82. Direct evidence was obtained that the 

 strong lines of the y ray spectrum of radium B were 

 identical with the corresponding lines in the X-ray spectrum 

 of lead — thus confirming the hypothesis that radium B and 

 lead have in general identical physical and chemical pro- 

 perties, although their atomic weights differ probably by 

 seven units. 



In the present paper an account is given of further experi- 

 ments to determine the 7-ray spectra of the very penetrating 

 rays from radium B and radium C. The strong lines from 

 radium B, which are reflected from rock-salt at angles of 10° 

 and 12°, undoubtedly supply the greater part of the soft 

 radiation for which /x = 40 (cm.)" 1 in aluminium. There still 

 remained the analysis of the frequency of the lines included in 

 the penetrating radiations from radium B, for which /x = 0'5, 

 and from radium 0, for which fi= 0*115. It may be 

 mentioned at once that there is undoubted evidence that a 



* Communicated bv the Authors. 

 t Phil. Mag-. May 1914, p. 854. 



