728 Prof. Rutherford and Mr. Richardson : Analysis 



Analysis of the soft radiation. 



In order to find the absorption coefficient of the very soft 

 radiation, which is shown so prominently in fig. 2 B, sheets 

 of aluminium *042 and *084 mm. thick were used. The 

 curve obtained is shown in fig. 4. In deducing the ioniza- 

 tion due to these soft rays 3 it is necessary to subtract the 



Fig. 4. 



Absorption of y rays from radium B-J-C. Initial portion 

 of curve X = 40. 



12 1-6 2-0 



Mms of Aluminium. 



2-4 



ionization due to the harder rays. This can easily be done 

 since the absorption of the harder rays over the thickness of 

 1*51 mm. of aluminium is practically linear. The difference 

 curve is exponential and gives an absorption coefficient in 

 aluminium /^ = 40. The source of y rays in this case was 

 about 15 cm. from the ionization chamber. In these ex- 

 periments, the pole-pieces were covered with thick card- 

 board in order to reduce the excitation of secondary y rays 

 to a minimum. With the bare pole-pieces close together, 

 the radiation entering the ionization vessel was distinctly 

 softer with a value of //, between 40 and 45. 



Attempts to detect very soft 7 radiation. 



Special experiments were made to examine whether 

 radium B or radium C emitted any very soft types of 7 

 radiation in addition to the type already discussed for which 

 /x = 40. In the experiments with the emanation tube, the 

 7 rays before entering the ionization vessel passed through 



