693 



TABLE 761.— RELATIVE IONIZATION PRODUCED IN VARIOUS GASES BY 

 HETEROGENEOUS X-RAYS* 



Density 

 relative 

 Gas or vapor to air = 1 



Hydrogen, H 2 07 



Carbon dioxide, CO* 1.53 



Ethyl chloride, GH 5 C1 2.24 



Carbon tetrachloride, CCU 5.35 



Nickel carbonyl, Ni(CO>4 5.90 



Ethyl bromide, GH 5 Br 3.78 



Methyl iodide, CH 3 I 4.96 



Mercury methyl, HgCCRa)* 7.93 



Ionization relative to air = 1 



For reference, see footnote 236, p. 692. 



TABLE 762. 



-WAVELENGTHS OF FLUORESCENT RADIATION 

 BY X-RAYS * 



EXCITED 



Region 

 Material A 



Fluorspar 3640-2400 



Fluorspar and iron spar 3900-2310 



Scheelite (Ca tungstate) 4800-3750 



Zinc sulfide 5090-4120 



K platinocyanide 4900-4120 



Ba platinocyanide 5090-4420 



Ca platinocyanide 5090-4550 



U NH« fluoride 4400-3800 



X-ray tube glass 5090-3000 



Position 



of maximum 



A 



2840 

 2800 

 4330 

 4500 

 4500 

 4800 

 4800 

 4100 

 3750 



For reference, see footnote 236, p. 692. 



TABLE 763.— THE ABSORPTION OF X-RAYS 



The absorption of X-rays by materials follows the same law as the absorption of 

 radiant energy, i.e., 



/ = /. X e-» x 



where h is the initial intensity and / the intensity after a distance x, and p. the absorption 

 coefficient, p./p is the mass absorption (p density) of the material, p./p is really the sum of 

 two coefficients — r/p the true or fluorescent X-ray mass-absorption coefficient — and a/p 

 the mass-absorption due to scattering. For light elements a/p has a practically constant 

 value of 0.17 independent of the wavelength for intermediate ranges. 

 The following relations may be written 



n/p = r/p + a/p = K\" + a/p 



The constants for this absorption equation for several materials follow : * 



* For reference, see footnote 236, p. 692. 



TABLE 764.— APPROXIMATE LEAD THICKNESS REQUIRED TO REDUCE 

 RADIATION DOSAGE RATE TO 5 PERCENT OF USEFUL BEAM 21 " 



287 National Bureau of Standards Handbook 41, Medical X-ray protection up to two million volts. 

 SMITHSONIAN PHYSICAL TABLES 



