690 



Mr. W. H. Jenkinson 



^-02 



and was found to be "00488 from the mean of several leakage 

 curves. ^ varies from test to test and is given for each 



thickness in column 4, Table I. In column 5 are the corrected 

 E.M.F.'s E. 



A rough comparison of the results may be made with 

 formula 1, by making use of a curve published by Madame 

 Curie* in which are plotted the logarithms of the intensity of 

 the /3 radiation from radium which has penetrated different 

 thicknesses of aluminium. 



If we know the equivalent thickness of Al through which 

 the rays have passed before they reach the unshielded electrode, 

 then log p and log p x may be read off directly from this 

 curve, and E may be calculated by equation (1). 



Assuming that the mica covering of the tube of radium was 

 '2 mm., the equivalent thickness of Al of this, the 4*5 cm. 

 of air and *05 mm. of Al, would be *3 mm. Using this value 

 the E.M.F.'s given in curve A (fig. 3) were obtained. Curve 

 B is the experimental curve. 



Fig. 3. 







1 A 















/ 





_, - 





B 















/' 























1 

 i 









C 













"T~~ 









































3 4 5 6 



Thickness of shielding Al. in mm. 



Po/pi may also be estimated in another way from the 

 experimental curves themselves, a the internal conductance 

 of the cell can be looked on as being made up of two parts 

 in series, a that of the unshielded region between the elec- 

 trodes, and a x that of the shielded region, and p jpi can be put 



* Curie, ' Radioactivity ' tome ii. p. 66. 



