4 A. S. Eve — Radium in Minerals by the ^-Radiation. 



Art. II. — The Measurement of Radium in Minerals by the 

 ^-Radiation • by A. 8. Eve. 



The usual method of determining the amount of radium 

 in a mineral is by measuring the maximum activity of the 

 emanation obtained from a solution. Good results have been 

 obtained in this way by Strutt, and by Boltwood. Again, the 

 quantity of uranium present is usually found by chemical 

 analysis ; and a measure of the active matter in a sample of 

 pitchblende can be found by observing the a-radiation from a 

 fine powder constituting an average sample of the mineral. 



In the present paper, an account will be given of another 

 method capable of giving equally accurate results. It was due 

 to a suggestion by Professor Rutherford that it would be 

 interesting to ascertain if radium E emitted 7-rays. This was 

 to be expected because he had already proved that radium E 

 gave rise to /3-rays, and in all known cases these are accom- 

 panied by 7-rays, and are probably their immediate cause. In 

 a newly prepared sample of radium bromide, there has not 

 been sufficient time for the growth of the slow transformation 

 products, so that very little radium E is present. But urani- 

 nite, which emits but a small fraction of its emanation, must 

 necessarily contain radium E almost in an equilibrium amount. 



The results of some preliminary experiments have been pub- 

 lished in a recent number of the Philosophical Magazine.* 

 The writer proved that the 7-radiations from radium, thorium 

 and radio-thorium were practically identical in character, being 

 very penetrating and absorbed to an equal degree by lead. 

 On the other hand, the 7-rays from uranium and actinium 

 were feeble and readily absorbed. It is, therefore, possible to 

 cut off the 7-rays arising from uranium or actinium in a sub- 

 stance, and yet to have a strong 7-radiation, due to radium or 

 thorium, penetrating the screen. In this way it is easy to 

 measure the amount of radium or of thorium present in any 

 ore, or in a solution, and the active substance need not be 

 powdered, or dissolved, or removed from bottle or test tube. 

 It is only necessary to place the substance under a lead screen 

 about one centimeter thick and to observe the fall of the gold 

 leaf of the electroscope. Then a standard of known magni- 

 tude, consisting of radium or thorium, is similarly placed, and 

 the fall of potential is again observed for the same period as 

 before. The saturation-currents in the two cases are propor- 

 tional to the quantities of radium or of thorium present. This 

 method of determining the amount of radium or of thorium 

 *A. S. Eve, Phil. Mag., April, 1906. 



