388 



Tables 494^98. 



RONTGEN (X-RAYS) RAYS. 



TABLE 494. — Corpuscular Rays. 



Corpuscular rays are given off in greatest abundance when radiator emits its characteristic radiation. Intensity 

 increases with atomic weight (4th power, Moore, Pr. Phys. Soc.). Greater number emitted at right angles to incident 

 rays. Velocity range (6 to 8.5)10' cm/sec. vo = velocity when leaving radiator = io^(,A = Atomic weight) = critical 

 velocity necessary to excite characteristic radiation, therefore corpuscular rays have practically the same velocity as 

 the original generating cathode rays. Are of uniform quality when e.xcited by characteristic rays and follow expyonen- 

 tial law of absorptioa in gases. If A is the absorption coefficient and A the atomic weight, X^* = Xvo* = constant 

 (Whiddington, Beatty), X is defined by / = /o e"^" where / and /o are the intensities after and before absorption and 

 d the thickness of the absorptive layer in cm. The following values for X in air for characteristic radiations from various 

 substances are due to Sadler. (At 0° C and 76 cm Hg.) 



TABLE 495. — Intensity of X-Rays. Ionization. 



The intensity of the radiation from an X-ray bulb is proportional to the current. Except at low voltages it equals 

 Ki{i/i — vo') where i is the current, a the applied voltage, do the break-down voltage and K a constant for the tube (KrOnke). 

 The intensity of X-rays is most accurately measured by the ionization they produce. This may be referred to the 

 International Radium Standard (see Table 508). It is proportional to the 4th power of the speed of the parent cathode 

 rays (Thomson), (true only of independent rays, Beatty, 1913). The saturation current due to X-ray ionization is 

 usually of the order of lo'^" to 10"" ampere. When X-rays pass through a substance, only once in a while is an atom 

 struck, only perhaps i in a billion, and ionized. The ionization is probably an indirect process through the mediation 

 of corpuscular rays. In the absence of secondary radiations the ionization is proportional to the mass of the gas 

 (that is, its pressure at constant temperature). It depends on the nature of tl^e gas, but is little afiected by the quality 

 of the rays. The following results are due to Crowther, 1908. 



Smithsonian Tables. 



