166 



On the Ionisation of Various Gases by the 

 <L Particles of Radium-No. 2. 



By \V. H. Beagg, M.A., Elder Professor of Mathematics and 

 Physics iv the University of Adelaide. 



^Read October 2, 1906.] 



Plate VII. 



Introduction. 



In a paper with a similar title (Proc. Roy. Soc. of South 

 Australia, vol. xxx., p. 1) I have given a preliminary account 

 of an attempt to determine the relative amounts of ionisation 

 produced in various gases and vapours by the a particle of 

 RaC. The present paper contains an account of the further 

 progress of this work. 



In the first place I have here discussed, the validity and 

 the experimental details of the method used, and have brought 

 forward evidence in favour of the liyjDothesis that 8i, the 

 ionisation produced in consequence of the expenditure of a 

 small quantity of energy Se by the a particle, is related to 

 the latter quantity by the equation Si = k f fvj Se, where /(vj 

 is a function of the velocity of the particle only, and k a con- 

 stant for each gas. 



Secondly, I have given the result of the attempts to deter- 

 mine for several gases the constant /.-, which may be called the 

 specific ionisation of a gas for a radiation, air being taken 

 as the standard. 



In conclusion I have discussed very briefly the form of 

 the function ffvj, and such conclusions as it seems legitimate 

 to draw from the results so far obtained. Amongst these is 

 the following: — The ionisation per molecule {ks, where s is 

 the stopping power) is closely connected to the molecular 

 volume. 



§ 1- 



The method of this research has already been described 

 briefly in the preliminary paper floe cit.J. For the sake of 

 clearness, however, and in order to facilitate a discussion of the 

 validity and the experimental details of the method, it will be 

 well to insert a short description here also. 



A small platinum plate is coated with a very thin layer 

 of radium bromide, and placed below a horizontal ionisation 

 chamber of 3 mm. width, at a distance which can be altered 

 at will. (See pi. vii.). A set of narrow vertical tubes is 



