332 Messrs. Moseley and Robinson on the Number of 



The Ionization produced by the 7 rays of Radium C. 



We desire to modify the value 1'3 x 10 15 previously given * 

 for the total ionization produced by the 7 rays. This value 

 was obtained from measurements of the ionization when all 

 the primary /3 rays were stopped by an aluminium cylinder 

 0*95 cm. thick. 



The results of measurements made under these conditions 

 are shown in Table I. 



Table I. 



7 ray ionization. 



(Uncorrected for absorption by aluminium.) 



Distance. 



nr\ 



103 cm 



5-84 X 10 9 

 564 X 10 9 

 5-28 X 10 9 

 531 X 10 9 

 5-42 X 10 9 

 545 X 10 9 

 5-54 X 10 9 

 5-59 X 10 9 

 5-68 X 10 9 



203 cm 



300 cm 



400 cm 



500 cm 



600 cm 



700 cm 



800 cm 



900 cm ... 



(It will be seen from the table that the condition expressed 

 by equation (2), namely, that nr 2 should be constant except 

 for the unimportant factor e~i J - r , is only approximately satis- 

 fied. The reason for this variation will be discussed later.) 



The results were then multiplied by the factor 1*14 to 

 correct for the absorption by the aluminium, and the total 

 ionization calculated by means of equation (3), assuming 

 Chadwick's value t '000059 cm." 1 for /*. 



Through the kindness of Sir Ernest Rutherford and 

 Mr. H. Richardson, we have been permitted to examine 

 some unpublished absorption curves obtained in connexion 

 with their work on the " Analysis of the 7 rays from radium 



* Rutherford, Kadioactive Substances, etc., p. 295, 1913. 

 t Chadwick, Proc. Phys. Soc. xxiv. p. 152 (1912). 



