Beta Rays and by Gamma Rays from Radium C. 557 



At the same distance, with the same amount of radium C, 

 we have 



using accented letters throughout for 7 rays, and unaccented 

 for yS rays. 



By division, q/q' = l$/K' . £~ Mr . and as K' has been found, 

 suitable experiments determine K. 



1. A capsule, containing radium bromide (\33 mg. radium) , 

 backed by ebonite and covered with thin mica, was placed 

 at 1 m. from the centre of the electroscope. The /3 and 7 

 rays together caused a leaf-movement of 12*2 divisions/ 

 minute, and the 7 rays alone of 0*4 division / minute. 

 Since 6^=1-4, it follows that K/K' = 11'8 x 14/'4=41. 

 This is, however, too large, on account of the /3 rays from 

 radium B reaching the electroscope. Kovarik * has found, 

 with aluminium screens, //,= 13 for radium C, and fi=7o for 

 radium B. 8ince ^ = '0033 for air in the case of the ft rays 

 from radium C, /x = '019 for the /3 rays of radium B. If 

 there are equal numbers of /3 particles from these two 

 products, it can be readily shown that the (3 rays from 

 radium C alone gave 10" 9 D/ra, corrected for air-absorption, 

 so that K/K' = 27. Tin's method involves some uncertainty. 



2. A glass tube containing '52 mg. of radium was placed 

 at 75 cm. distance from the centre of the electroscope. The 

 f3 rays gave 16*9, and the 7 rays "85 division/minute. The 

 correction factor for air-absorption is 1*25, and for the glass 

 walls about 1*40. The /3 rays from radium B were mainly 

 absorbed. Thus 



K/K' = i|| X 1-28 x 1-40 = 35. 



CO 



There is much uncertainty, however, in the correction for 

 absorption by the* glass walls, and by the radium bromide of 

 one-quarter of full strength. 



3. The most satisfactory method was the employment of a 

 thin aluminium leaf f'0012 cm.), which had received a coating 

 of the active deposit when negatively charged in the air 

 above a solution of 11 mg. of radium bromide in a flask. 

 Alternative readings for ft and 7 rays, and for the 7 rays 

 alone, were obtained, and the well-known decay-curve for 

 the active deposit was plotted from the results, so that the 

 ionization due to the (3 rays and to the 7 rays respectively,. 

 at the same instant, could be found by interpolation. The 



* Phil. Mag. Nov. 1910. 



