492 Mr Beatiy, A Dissymmetry in Emission of Cathode Particles 



On a Dissymmetry in the Emission of the Cathode Particles 

 which are produced by Homogeneous Bontgen Radiations. By 

 R. T. Beattv, M.A., B.E., Emmanuel College. (Commuuicated 

 by Professor Sir J. J, Thomson.) 



[Head 9 May 1910.] 



When Rontgen radiations fall upon certain metals, homo- 

 geneous secondary radiations are produced. If one places a thin 

 metallic sheet in the path of such a homogeneous radiation, 

 cathode particles will emerge from both surfaces of the sheet. 

 The object of the present research is to find out what ratio exists 

 between the quantities of cathode energy leaving the front and 

 back surfaces. 



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Fig. 1. 



A shallow cylindrical brass ionisation chamber (fig. 1) received . 

 the radiations through a thin parchment window PP in its lower 

 side. RR is a ring cathode. Two concentric circles were cut out 

 of a sheet of cardboard and an annulus was thus formed which 

 had an external diameter equal to that of the ring electrode, while 

 its internal diameter was about 2 cms, less. A silver leaf (equiva- 

 lent in weight to 2 mm. of air) was laid upon two sheets of thin 

 paper (each sheet being equivalent to 1 cm. of air) and the whole 

 was tightly gripped between two cardboard rings made as de- 

 scribed, and gummed at the edges. 



A second specimen was now made of the exact dimensions of 

 the first, but in this case the silver leaf was placed between the 

 two sheets of paper, the latter absorbing all the cathode particles 

 from the silver. 



These rings were placed in turn on RR, and the ionisation 

 measured when a given radiation entered through the window 

 PP. A second electroscope was used to standardise the radiation. 



Now in one cardboard ring the arrangement was paper — 

 silver leaf-paper. Let us call this ring since no cathode par- 

 ticles can escape through the paper. The second ring was made 

 up of silver leaf-paper-paper. We may call this C since cathode 

 particles do escape from one side of the leaf 



