416 Mr Beatty, The production of Cathode Particles 



The production of Cathode Particles by Homogeneous Rontgen 

 Radiations. By R. T. Beatty, M.A., B.E., Emmanuel College. 

 (Communicated b}' Prof. Sir J. J. Thomson.) 



[Bead 21 February 1910.] 



Several physicists have investigated the cathode particles 

 produced when Rontgen radiations fall upon various substances. 

 The recent work of Cooksey* and Innesf has shown that the 

 velocities of these cathode particles are independent of variations 

 in the intensity of the Rontgen radiations used, and are also 

 independent of the nature of the substance struck, but that the 

 velocities increase or decrease with an increase or decrease in the 

 penetrating power of the exciting Rontgen radiations. 



The discovery of homogeneous Rontgen radiations, emitted 

 by certain metals when exposed to suitable Rontgen radiations, 

 enables one to use definite beams which differ widely in penetrat- 

 ing power, and it seemed that by using such beams more definite 

 information might be gained about the cathode particles emitted 

 from metals placed in the path of such beams. 



When a very thin silver leaf was placed in the path of the 

 homogeneous radiations described above, cathode particles shot 

 out from its surface. It was determined to investigate the 

 coefficients of absorption of these cathode particles in air and in 

 hydrogen. Hydrogen was chosen on account of its anomalous 

 behaviour with regard to ionisation phenomena. 



The radiations from a Rontgen bulb, proceeding in a direction 

 normal to the plane of the paper (fig. 1) fell upon the metal 

 which acted as radiator. Plates of Fe, Ni, Cu, Zn, As, Sn were 

 used as radiators. 



A homogeneous radiation then proceeded from the radiator. 

 Part of this entered the cylindrical brass chamber A through the 

 thin parchment window. It then passed through the silver leaf, 

 and was finally totally absorbed in the thick brass disc DD which 

 served as electrode. DD was covered with paper to prevent the 

 emission of cathode particles from its surface. 



Another portion of the radiation entered the primary electro- 

 scope (fig. 1), which served to standardise the amount of homo- 

 geneous radiation emitted by the radiator. 



As the quality of the homogeneous radiation is unaffected by 

 variations in the bulb, and as the quantity of radiation entering 

 the chamber A is always the same fraction of that entering P 



" Cooksey, Am. Jour. Sci., iv. 24, 1907, p. 285. 



t Innes, Proc. Boy. Soc, Set. A, lxxix., Aug. 2, 1907, 



pp. 442—462. 



