CAA Tables 663 {continued) and 664 



RONTGEN RAYS (X RAYS) 



TABLE 663 {continued)- — Absorption and Scattering of X Rays; Fluorescence 



f i/ P =(i/A)(o.oi36Z i \ 3 + 0.32Z) \<\k 



fl/p—(l/A) (0.0020Z 4 X 3 + O.32Z) Xfc < X < \ Li 



p is the density, Z, the atomic no., A, the atomic weight of the material of the plate, X, 

 the wave length of the X rays, Angstrom units ; x is in cm. Values for Xfc and \l u wave 

 lengths at which materials have " critical absorption discontinuities," are listed in Table 657 

 under " X-ray Emission " as X a . Numerical values for fi/p, the " mass absorption coeffi- 

 cient," (A. H. Compton "X-rays and Electrons") are given in Table 665. 



The first term in the brackets represents energy losses from " fluorescent," or " true," 

 absorption ; this first appears as energy of ionization of atoms and of photoelectrons. The 

 ionized atoms then either emit characteristic X rays or use their energy for the photo- 

 electric process ; the quantitative relations between these are described in Table 660 under 

 " X-ray Emission." 



The second term is the energy lost by the X-ray beam by scattering. Except for the 

 (usually small) amount of energy which goes into the production of "recoil electrons," 

 it remains as X-ray energy which is simply redistributed as to direction of propagation, 

 being radiated in all directions from the plate. The scattered radiation is of two parts, an 

 "unmodified" (or "unshifted") part, and a "modified" (or "shifted") part. The 

 former has the wave length of the original beam. The wave length of the modified part 

 is longer (" Compton shift ") than that of the original beam by an amount 5X which varies 

 with 0, the angle between the direction of the primary beam (of wave length X), and the 

 direction of that portion of the modified rays of wave length X + 5X. The relation between 

 S\ and is 5X (Angstrom units) = 0.02428(1 — cos 0). 



TABLE 664. — X-Ray Absorption and Chemical Combination 



The wave lengths of the critical absorption limits of an element depend, to a very small 

 extent, on the chemical combination of the " absorbing " element. The K absorption limit 

 for phosphorus follows for various chemical combinations : R stands for any one of several 

 metals. 



Wave lengths, X, in Angstroms 



(RO) 3 PO 



(RO) 2 HPO 



(RO)HoPO 



(RO) 2 (RC)PO... 

 (RO)(RC) 2 PO... 



(RChPO 



(ROjPOR 



(RN)(Cl) 2 PO.. . . 

 (RN)(RO)(Cl)PO 

 (RN)(RO) 2 PO... 

 (RNh(RO)PO... 



(RN)sPO 



(RC) 3 PS 



RO(RC)(H)PO 



(RO) 3 P 



(RC)bP 



(RO)CI 2 P 



(RC) 3 P,CuCl.. 

 (RO) 3 P,CuCl.. 



P (violet) 



P (black) 



P (white) 



5-7565 

 5-7632 

 5.7581 

 5-7599 

 5.7676 

 5-7602 

 5-7645 

 S-7589 

 5.7714 

 5.7715 

 5-7769 



0.0058 

 .0125 

 .0074 

 .0092 

 .0169 

 .0095 

 .0138 

 .0082 

 .0207 

 .0208 

 .0262 



There result some conclusions probably of general application: (AX) in its value for 

 some particular compound, depends only on what atoms are directly attached to the 

 absorbing atom (e.g., the phosphorus limit (RO) 3 P does not depend on what metal is 

 used for R). AX depends on the kind of atom directly attached (compare (RO) 3 P with 

 (RC) 3 P) and on the number of these atoms (compare (RO) 3 P with (RO) 3 PO). If any 

 addition (any kind of atom) is made to a given set of atoms directly attached to the 

 absorbing one, the limit is shifted toward a shorter X (cf., (RC) 3 P with (RC) 3 PO). 

 Further, the wave length for the element when uncombined is usually greater than when at- 

 tached chemically to other atoms (true for all of 11 elements investigated except sulphur). 

 A variation of wave length is also usually shown for allotropic modifications of an element. 



Smithsonian Tables 



