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XXVI. y Radiation from Radium B. By H. G. J. Moseley, 

 B.A., and W. Makoweb, M.A., D.Sc* 



HPHE existence of a small amount of radiation from 

 JL radium B, of the same penetrating power as the hard 

 /3 rays from radium 0, has been demonstrated by H. \Y. 

 Schmidt t and confirmed by Fajans and Makower J. It 

 seemed, therefore, probable that radium B would emit a 

 small amount of hard 7 radiation of the same penetration as 

 that from radium C. This was, however, found not to be 

 the case ; but the investigation undertaken to detect these 

 rays has demonstrated the existence of soft 7 rays from 

 radium B which have hitherto escaped detection. Although 

 the complete study of this radiation has not yet been made, 

 the experiments so far carried out show the amount which 

 the new radiation contributes to the total 7-ray activity of the 

 active deposit of radium. It is also possible to deduce the 

 absorption coefficient of the radiation by lead, though not with 

 great accuracy since the number of experiments carried out 

 was small. 



The method of investigation adopted was the same ns that 

 used by Fajans and Makower in studying the /3 rays from 

 radium B, except that the measurements were all made 

 through sufficient lead to absorb all the /3 rays both from 

 radium B and from radium 0. Thus pure radium B was 

 prepared by recoil from radium A and the rise of the 

 7 radiation w T as measured through different thicknesses of 

 lead. The duration of the recoil was in some cases 30 seconds 

 and in others 90 seconds. If, as has hitherto been supposed, 

 all the 7 radiation from the active deposit of radium is due to 

 radium C, the activity should at first be nothing and rise to 

 a maximum after 33 minutes and then fall off with time. 

 In practice, however, it is impossible to obtain pure radium B 

 by the method of recoil, since in order to obtain sufficient 

 activity, it is necessary to prolong the recoil for a finite time. 

 The amount of ra iium C formed during the recoil can be 

 calculated and the effect produced on the results allowed for ; 

 this has been done throughout in calculating the theoretical 

 curves. The curves in fig. 1 have been calculated for the 

 case in which the recoil lasted 30 seconds — curve A on the 

 assumption that the activity is due wholly to the 7 rays from 

 radium C, and curve B on the assumption that 7 rays from 

 radium B also contribute to the activity. In curve B the 



* Communicated by Prof. E. .Rutherford, F.R.S. 

 t H. W. Schmidt, Annalen der P/iysik, xxi. (1906). 

 X Fajans and Makower, supra, p. 292. 



