THE 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



Art. XXXIX. — On the Relative Activity of Radium and 

 Thorium, measured oy the Gamma-Radiation y by A. S. 

 Eve. 



The recent work of Boltwood* and of Dadourianf proves 

 that about one-half of the radio-thorium in radio-active min- 

 erals is abstracted in the chemical processes of preparing the 

 commercial salts of thorium. This fact was established inde- 

 pendently by the two observers, the one measuring the a-activ- 

 ities of the minerals and the salts, the other comparing the 

 activities of their respective emanations. Thus they found per 

 gram of thorium more radio-thorium in thorianite than in 

 thorium nitrate, the ratio being about 2*1 or 2*6 to 1. Bolt- 

 wood further states that " the specific activity of thorium with 

 its equilibrium quantities of disintegration products is constant. 1 ' 



The present paper deals with the following points : — 



I. To determine the ratio of the gamma-activities of radium 



and thorium when both are in radio-active equilibrium. 



II. To ascertain the relative amounts of radio-thorium in thori- 



anite and thorium nitrate respectively, by measurement 

 of the gamma-radiations. 



The object of the experiment was not to verify the work of 

 Boltwood and of Dadourian, but to test the 7-radiation method, 

 ascertaining if the results obtained by it were in good agree- 

 ment both with the a-ray method and with the emanation 

 method. Such was found to be the case. 



* This Journal, June, 1906, pp. 409, 415. \ Ibid., p. 427. 



Am. Jour. Sci. — Fourth Series, Vol. XXII, No. 132. — December, 1906. 

 33 



