Tables 390-392. 

 RONTGEN (X-RAYS) RAYS. 



335 



Rontgen rays are produced whenever an electric discharge passes through a highly exhausted 

 tube. The disturbance is propagated in straight lines probably with the velocity of light, affects 

 photographic plates, excites phosphorescence, ionizes gases and suffers neither deviation by mag- 

 netic forces nor measurable refraction in passing through media of different densities. With ex- 

 treme exhaustion in the *;ube they have an appreciable effect after passing through several milli- 

 meters of brass or iron. The quality by which it is best to classify the rays is their hardness 

 which is the greater the greater the exhaustion. It is conveniently measured by the amount of ab- 

 sorption which they suffer in passing through a layer of aluminum or tin foil of standard thick- 

 ness. The number of ions which the rays produce in i sec. in passing through i cu. cm. of a gas 

 depends upon its nature and pressure. The absorption of any substance is equal to the sum of 

 the absorption of the individual molecules and the aljsorption due to any molecule is independent 

 of the nature of the chemical compound of which it forms a part, of its physical state, and probably 

 of its temperature. 



TABLE 390. — Ionization due to Rontgen Rays in Various Qases. 



Strutt, Proc. Roy. Soc. 72, p. 2og, 1903 ; Eve, Phil. Mag. 8, p. 610, 1904. 



When Rontgen rays pass through matter they produce secondary Rontgen rays as well as cath- 

 odic rays. The former are of two types : the first is like the original rays and may be regarded as 

 scattered primary rays; the second type varies with the nature of the material struck and is in- 

 dependent of the primary rays. If the atomic weight of the material struck is less than that of 

 Calcium then the first type alone is present. The higher the atomic weight of the material struck 

 the more penetrating is the secondary radiation given out. This is shown in the following table 

 where A is the reciprocal of the distance (cm.) in Al. through which the rays must pass in order 

 that their intensity is reduced to 1/2.7 o^ ^^^ original intensity. 



The secondary cathodic rays seem to be independent of the material struck and of the intensity 

 of the original rays. The velocity of these secondary rays depends upon the hardness of the orig- 

 inal rays. The following table gives the thickness in cm. of the gas at 760 mm., 0° C. neces- 

 sary to reduce the energy of the cathodic rays to one half (t) as well as K as above defined. 



TABLE 392. — Rontgen Secondary Cathodlo Rays. 



Smithsonian Tables. 



Beatty, Phil. Mag. 20, p. 320, 1910. 



