240 



Mr. D. C. H. Florance 



energy given up by the secondary 7 radiation is not strictly 

 comparable with the energy given up by the primary y rays. 

 If this is the case then the distribution observed by means of 

 an electroscope filled with air would not be a measure of the 

 real distribution of the energy of the primary and secondary 

 radiations. An experiment was carried out to determine the 

 distribution of the secondary radiation when the electroscope 

 contained a mixture of hydrogen and methyl iodide. The 

 radiators used were '326 cm. lead and "5 em. zinc, and the 

 results are compared in Table VI. with tho.^e obtained when 

 air was the gas in the electroscope. 



Table VI. 



i 



! 



Radiators. 



E v 



E, 



E 3 . 



E 4 . 



i 



Air XIethyl 



1 iodide. 



! Air. 



30 



! 77 



Methyl 



iodide. 



32 



78 



Air. 



Methyl 

 iodide. 



| Air. kto 1 

 iodide. 



0'326 cm. lead.. 

 0*5 cm. zinc ... 



100 100 

 192 190 



23 

 53 



29 

 57 



42 I 63 

 90 100 



The ionization current when the electroscope was in 

 position E 2 and the radiator was lead, has been taken equal 

 to 100. The side of the electroscope was '202 cm. aluminium. 

 It is at once seen that the observed distribution depends 

 largely on the gas within the electroscope. This is especially 

 noticeable when lead is the radiator. This result supports 

 the view that a softer radiation is produced in the lead, and 

 this is most marked on the incident side of the plate. The 

 values obtained for the absorption coefficients of the secondary 

 radiation will also to a certain extent be dependent on the 

 fact that the softer radiation gives up a greater proportion 

 of its energy. 



The Energy of the Secondary Radiation. 



The range of distribution examined was of necessity limited, 

 and therefore, to determine the total secondary radiation, 

 a comparison was made with earlier experiments, and 

 approximate values have been assigned in the unexplored 

 parts of the field. The energy of the primary radiation 

 falling on an aluminium radiator 1*3 cm. thick was calcu- 

 lated. Then an approximate estimation was made of the 

 total secondary radiation by graphically integrating over 



