Section III, 1921 [lOli Traxs. R.S.C 



071 the Variation of the "Emanating Power" of Certain Uranium 

 Minerals with Temperature and a New Secondary Radium Emana- 

 tion Standard ' 



By J. H. L. JoHxsTOXE, M.B.E., Ph.D. 



Presented by Professor H. L. Bronsox, F. R.S.C. 



(Read May Meeting, 1921) 

 Introduction 



The usual method for the determination of small quantities of 

 radium depends upon the separation and collection of the radium 

 emanation which is in equilibrium with the radium present in the 

 material under examination. The activity of this emanation is 

 determined in a suitable electroscope or other testing device and is 

 compared with the activity of the emanation in equilibrium with a 

 known quantity of radium. A similar method is used for determining 

 the radioactivity of natural waters. 



Ln the type of measurement referred to, the amounts of radium 

 which can be conveniently estimated are of the order of lO-'-* gram. 

 The preparation of a suitable "standard" radium solution is attended 

 with considerable difficulty since the accurate measurement of a 

 quantity of radium less than 10-^ gram by means of the gamma 

 radiation is practically impossible.'- Amounts of radium of the order 

 of 10-'^ gram must, therefore, be used and the solution must be diluted 

 to a considerable volume in order to attain the strength necessary 

 for this purpose. Another difficulty in the case of dilute radium 

 solutions is the belief expressed in many quarters that such solutions 

 are not permanent but tend, on standing, to deposit a portion of the 

 contained radium.'' Moreover, when a standard solution is used for 

 the calibration of the electroscope, the process of l)oiHng off the 

 emanation, collecting it, drying the gas, and introducing it into the 

 electroscope is necessarily a somewhat complicated and troublesome 



^ The experimental work which is reported in this paper was carried out in the 

 Sloane Physical Laboratory of Yale Univ^ersity in 1916. The chief reason for the 

 delay in publication was the author's entry into active service with H. M. forces. 

 The author expresses his thanks to Prof. B. B. Boltwood of Yale l^ni\ersity for 

 suggesting this problem and for his kind advice and interest. 



- W. Bothe, Phys. Zeit. 2, P. 33, 1915 



^ Professor Boltwood has found that the addition of hydrochloric acid to the 

 radium solution prevents this deposition. 



