386 



Tables 489-491. 



RONTGEN (X-RAYS) RAYS. 



TABLE 489. — Cathode and Canal Rays. 



Cathode (negative) rays consist of negatively charged particles (charge 4.77 x lo"'" esu, 

 1. 591 X lo"*' emu, mass, 9 x 10"^^ g or 1/1800 H atom, diam. 4 x io~^' cm) emitted at low 

 pressures in an electric discharge tube perpendicularly to the cathode (/. can be focused) with 

 velocities (10* to 10'" cm/sec.) depending on the acting potential difference. When stopped by 

 suitable body they produce heat, ionization (inversely proportional to velocity squared), photo- 

 graphic action. X-rays, phosphorescence, pressure. The bulk of energy is transformed into 

 heat (Pt, Ta, W may be fused). In an ordinary X-ray tube carrying 10""^ ampere the energy 

 given up may be of the order of 100 cal/m. Maximum thickness of glass or Al for appreciable 

 transmission of high speed particles is .0015 cm. Maximum velocity Vd with which a cathode 

 ray of velocity Vo may pass through a material of thickness d is given by Vo* - V/ = adx 10^"; 

 a = 2 for air, 732 for Al and 2540 for Au, cm-sec. units (Whiddington, 1912). Cathode rays 

 hav« a range of only a few millimeters in air. 



Canal (positive) rays move from the anode with velocities about 10^ cm/sec. in opposite 

 direction to the cathode rays, carry a positive charge, a mass of the order of magnitude of the 

 H molecule, cause strong ionization, fluorescence (LiCl fluoresces blue under cathode, red under 

 canal ray bombardment), photographic action, strong pulverizing or disintegrating power and 

 by bombardment of the cathode liberate the cathode rays. 



TABLE 490. — Speed of Cathode Rays. 



The speed of the cathode particles in cm/sec. as dependent upon the drop of potential to 

 which they owe the speed, is given by the formula v = 5.95 VjE-io'. The following table gives 

 values of 5.95 "V^E. 



For voltages 1000 to 10,000 multiply 2d line by 10, etc. 



TABLE 491. — Cathodic Sputtering. 



The disintegration of the cathode in an electric discharge tube is not a simple phenomenon. 

 The particles taking part in the sputtering must be either large or of high speed or both (2000-1- 

 gauss field required for their deviation). It depends upon the nature of the residual gas. H, N, 

 CO2 are not generally favorable; Ar is especially favorable, also He, Ne, Kr and Xe. Raised 

 temperature favors it. The relative sputtering from various metals is shown in the following 

 table (Crookes, Pr. R. S. 1S91); the residual gas was air, pressure about .05 mm Hg. 



For further data on cathode, canal and X-rays, see X-rays by G. W. C. Kaye, Longmans, 

 1917, upon which much of the above and the following data for X-rays is based. See also J. J. 

 Thomson, Positive Rays, Longmans, 1913. 



Smithsonian Tables. 



