JOUENAL OF THE COLLEGE OF SCIENCF, TOKYO IMPERIAL UNIVERSTTY. 



Vol. XXXVII., Article 10. 



On the Photographic Action of a, ß and r 



Rays emitted from Radioactive 



Substances. 



By 



Suekichi KiNOSHITA, Ui<j<ikuhah-us]ii. 



and 



Hadime IKEUTI, lH'jakushi. 



Wit It S Plates. 



1. Introduction. In 1909 one of the writers^^ showed that 

 whenever an « particle strikes a grain of silvei* hahcle in the 

 sensitive fihii of photographic phites, that grain becomes suh- 

 sequently caj^able of development. It was also shown that this 

 is the case throughout the whole range of « rays, no matter what 

 may be the quality of the plate. It is remarkable that the 

 behaviour of the photographic plate regarding this phenomenon 

 should obey such a simple law, when we take into consideration 

 its complex behaviour with regard to light. 



From the atomistic point of view, on the other hand, the above 

 result is also highly interesting, as it affords a third independent 

 method of recording the emission of a single a particle, in addition 

 to the electrical method devised by Kutherford and Geiger^\ and 

 the scintillation method first systematically studied by Regener^\ 



In the light of the above investigation, it was to be 

 anticipated that if a particles were projected tangentially on a 

 photographic plate, the halide grains encountered by each « 

 particle would on development appear in a train. This effect 



1) S. Kinoshita, Proc. Eoy. Soc. A, 83 (1910), p. 432. 



2) E. Eutherford and H. Geiger, Proc. Eoy. Soc. A, 81 (1908), p. 141. 



3) E. Eegener, Verh. d. D. Pliys. Ges. 10 (1908), pp. 78 and 351. 



