906 Mr. F. P. Slater on Excitation of 7 Radiation 



an experimental curve, obtained when india paper, con- 

 taining atoms of low atomic number only, was bombarded 

 by a particles, was taken as the standard from which 

 measurements were made. 



The results obtained clearly indicate that a small quantity 

 of hard 7 radiation is produced when the a particles from 

 radium emanation impinge on metals like tin and lead, 

 the origin and nature of which will be discussed later in this 

 paper. The evidence for ascribing its origin to close en- 

 counters between the ol particles and the nuclei of the atoms 

 in the target is based on the nuclear constitution of the 

 atom as put forward by Sir Ernest Rutherford *. This has 

 been confirmed from so many widely different sources that 

 in these considerations its truth is assumed implicitly. 



PART II. 



The same method as in Part I. is extended to investigate 

 the soft radiations generated by the impact of a particles on 

 metallic elements. It is indicated that with the elements 

 of high atomic number at least two types ot radiation are 

 emitted of quality differing considerably from the very 

 penetrating type investigated in Part I. The two types 

 correspond roughly with the respective "K" and " L " 

 radiations of the elements bombarded ; and considering the 

 smallness of the quantities to be measured, the difficulties 

 encountered, and the assumptions made, the agreement is as 

 close as can be expected. 



With an element like tin (medium atomic number), one 

 type only is indicated — other than the hard type of Part I. — 

 which is of the same order as its characteristic "K" radia- 

 tion. Any radiation of characteristic " L " order would be 

 indetectable under such conditions. 



The term " lead radiation/'' as used in this paper, means 

 the radiation excited when the ol particles impinge on a lead 

 target, and similarly for the term " tin radiation " etc. 



Paet I. 



Method. 



The radiation was measured by an ionization method, and 

 a diagrammatic sketch of the apparatus used is given in 

 fig. 1. The electroscope was cylindrical in shape, having 

 inside dimensions 21 cm. diameter and 22 cm. height. The 

 whole was made of lead, some hundreds of years old, to 



* Rutherford, Phil. Mag. xxi. p. 609 (1911). 



