TABLES 496-497. 



RONTGEN (X-RAYS) RAYS. 



TABLE 496. Mass Absorption Coefficients, \/d. 



The quality by which X-rays have been generally classified is their "hardness" or penetrating power. It is greater 

 the greater the exhaustion of the tube, but for a given tube depends solely upon the potential difference of the elec- 

 trodes. With extreme exhaustion the X-rays have an appreciable effect after passing through several millimeters of 

 brass or Al. The penetrability of the characteristic radiation is in general proportional to the sth power of the atomic 

 weight of the radiator. The absorption of any substance is equal to the sum of the absorptions of the individual atoms 

 and is independent of the chemical combination, its physical state and probably of the temperature. Most of the 

 following table is from the work of Barkla and Sadler, Phil. Mag. 17, 739, 1909. For starred radiators, L radiations 

 used; for others the K. 



If 7o be the intensity of a parallel beam of homogeneous radiation incident normally on a plate of absorbing material 

 of thickness /, then I = I e~^ x gives the intensity / at the depth x. Because of the greater homogeneity of the secondary 

 X-rays they were used in the determination of the following coefficients. The coefficients X have been divided by the 

 density d. 



TABLE 497. Absorption Coefficients of Characteristic Radiations in Gases. 



The penetrating power of X-rays ranges in normal air from i to 10,000 cm or more. The absorptive power of i 

 cm air = 1/820 that of water. X (see preceding table for definition) for air for soft bulb (1.5 to 5 cm spark gap, 4 to 

 10 m air) ranges from .0010 to .0018; for hard bulb (30 cm spark gap, 4 to 10 m air), .00029. (Eve and Day, Phil. 

 Mag. 1912.) The absorption coefficient for gases for characteristic or monochromatic radiations varies directly with 

 the pressure. For different characteristic radiations it is proportional to the coefficients in air. It varies with the sth 

 power of the atomic weight of the radiator. The following table is taken from Kaye's X-rays and is based on the work 

 -of Barkla and Collier (Phil. Mag. 1912) and Owen. All are for the gas at o C and 76 cm Hg. 



SMITHSONIAN TABLES. 



