Polonium, Radium, and Radioactinium. 



123 



The absorption of the 7-radiation of radium at the time of 

 its minimum activity was compared with that of radium in 

 equilibrium with its products, radium A, B, and C. In the 

 first column of Table I. below is given the thickness of 

 aluminium, in the second are the intensities of the radiation 

 from radium in equilibrium with radium A, B, and C, through 

 these thicknesses, where the initial intensity has been put at 

 100, in the third the relative intensities of the y-radiation, 

 from radium at its minimum activity. The table shows that 

 the y-rays of radium itself are much less penetrating than 

 those of its products radium* B and C. 



Table I. 



Thickness of Aluminium 



Intensity of 

 y-rays from 



Intensity of 

 y-rays from 

 radium itself. 



(cm.). 



Ea-f-Ea(A+B + C) 





in equilibrium. 





•008 



100 



100 



•057 



97-6 



87 



•133 



945 



78 



•266 



— 



72 



•323 



91-3 



— 



1-0 



81-6 



62 



1-3 



— 



56 



2-0 



73-9 



45 



2-3 



— 



33 



The intensity of the y-radiation of radium was about 1 to 

 1J per cent, of that of radium and its products in equilibrium 

 measured through 0*1 cm. of aluminium. This percentage 

 would be less if the measurements were conducted through 

 a greater thickness of aluminium or of lead. 



Absorption measurements of the radium y-rays by small 

 thicknesses of aluminium showed the presence of a very soft 



type of radiation which had a value of ^ between 100 and 



150. The amount of this type varied between 1*5 and 

 2*5 div. per min. according to the distribution of the active 

 material. Owing to the growth of emanation and of radium 

 B and C, the y-ray activity began to rise steadily after an 

 hour. Emanation also diffused into the electroscope and 

 increased the natural leak. Consequently it was difficult to 

 make accurate measurements, and though it can be said 

 definitely that radium emits three types of y-radiation, the 

 absorption coefficients given are only approximate. The 

 softest type gave about 2 div. per min., and had a value of 



