﻿7 Radiation from Radium B. 305 



by a thin plate of aluminium. The surface coated with 

 radium B, which in this case was entirely uncovered, was 

 placed in front of the aluminium plate. Two experiments 

 were made in which the absorbing sheets of lead were 

 0*97 mm. and 1*72 mm. respectively. The results indicated 

 that for radium B and radium Cin equilibrium 16*7 per cent, 

 of the ionization is due to radium B when measuring through 

 0'97 mm. of lead, and 12*3 per cent, through 1*72 mm. of lead. 



It is evident that the radiation from radium B is much 

 softer than that from radium C An idea of the coefficient 

 of absorption of the radiation by lead can be formed if it 

 is known how the radiation emitted by radium B and 

 radium in equilibrium is absorbed. This absorption was 

 found for the greater thicknesses of lead by using as the 

 source of radiation radium emanation enclosed in a glass 

 tube. For the smaller thicknesses of lead this source could 

 not be used on account of the necessity of doing away with 

 the glass envelope. In this case, therefore, a plate was 

 made active with radium B and measurements taken in the 

 neighbourhood of 33 minutes after preparation, at which time 

 the radium B and radium C produced from it were in 

 equilibrium. The absorption coefficient of the 7 rays from 

 radium B can then be calculated from the observations. 



It was found that the coefficient of absorption Xis 4 cm. -1 

 between 3 mm. and 6 mm. of: lead and is 6 cm. -1 between 

 0*97 and 1*72 mm. of lead. It will therefore be seen that 

 the 7 rays from radium B are much softer than the 

 penetrating radiation from radium C given by F. & W. M. 

 Soddy and Kussell * as having an absorption coefficient 

 0*5 cm."" 1 over a wide range. 



The method described above, though suitable for testing 

 whether there is any considerable 7 radiation from radium B, 

 is not the best possible for seeing whether there is a small 

 amount of hard y radiation emitted by this product ; for the 

 quantity of radium B obtainable by the method of recoil is 

 not great, so that a small amount of hard radiation might 

 escape detection. A better method of testing the point is to 

 observe the rise of activity of radium emanation, which has 

 been completely freed from the active deposit associated with 

 it. in such an experiment 7 rays from radium B make 

 themselves easily noticeable. This would appear to be the 

 best method of obtaining precise values for the absorption o( 

 the soft rays ; but on account of the doubtful significance oi' 

 such measurements, this investigation has not been pursued. 



* Phil. Masr. May 1910. 



