Tables 660 (continued)-6G3 c^o 



TABLE 660 (continued)- — Energy and Quality of Emission X Rays 



h is the intensity in the continuous X rays obtained outside the tube at a distance of 

 I meter from the focal spot, supposing no filtration other than the unavoidable filtration 

 due to the walls of the tube (assumed equivalent to 1.23 mm of Al), anticathode, etc. For 

 practical purposes, until more thorough data is at hand, h may be assumed proportional 

 to the atomic number of the material of the anticathode. It is expressed in ergs per sec. 

 falling on a 1 cm 2 surface perpendicular to the X-ray beam. The orientation of the tube 

 is supposed to be the usual one, with X rays taken off perpendicular to the cathode stream, 

 and target face inclined at 45 . h is a similar quantity for the K characteristic rays. 



c and k are quantities contained in p. 537, which describe the spectrum distribution of 

 the intensity h. 



Ei and E 2 are probably within 5% and 10%, respectively, of their correct values. 

 h and h depend on the tube walls, the roughness of the target surface, etc., and on such 

 accounts an estimate of accuracy is difficult to make; for a smooth target surface, inclined 

 at 45°, and tube walls of 0.7 mm soda glass, the above values of h and h are probably 

 correct to within 20%. 



TABLE 661. — X-Ray Spectroscopy 



When an X-ray beam is incident on a crystal in such a manner as to make a glancing 

 angle 6 with certain sets of parallel planes within the crystal (adjacent planes, containing 

 large numbers of atoms, for best efficiency), these planes having an interplane spacing d, 

 components of the beam of wave lengths X, X/2, X/3, .... \/n will be diffracted (or 

 "reflected") according to the relation (Bragg law): X=2efsin0. The angle between 

 the directions of the original beam and the deviated beam is 20. Refraction in the crystal 

 would introduce an additional factor in the above formula, but the effect is negligible for 

 all ordinary work. 



Values for d, the " lattice constant," for some of the commonly used crystals are tabu- 

 lated below. 



TABLE 662. — Lattice Constants of Crystals 



d in Angstroms 



Crystal Surface at 18° C 



Carborundum (m) 2-49 



Rock salt Cleavage face 2.814 



Calcite Cleavage face 3 . 029 



Quartz Prism face 4-247 



Gypsum Cleavage face 7-577 



K 4 FeCN 6 (100) 8.408 



Mica Cleavage face 9-993 



Sugar (100) 10.57 



A1 3 3 (100) 11.23 



For an extensive tabulation of X-ray data on crystals see the I. C. T., vol. 1. 



TABLE 663. — Absorption and Scattering of X Rays; Fluorescence 



A beam of X rays loses energy as it traverses matter. For monochromatic rays, this loss 

 of energy is given by the formula : I/h = e-V-* where I« and / represent respectively 

 incident and emergent intensities of a parallel beam normal to a plate of absorbing 

 material of thickness x, e is the base of natural logarithms, and fi is a constant depending 

 only on the wave length of the x rays and the material of the plate. 



For the most used range (wave lengths 0.1 to 1.4 Angstroms, and atomic numbers 

 greater than 5; outside this range there are systematic deviations from the formulae) /i 

 is approximated to about 5% or better by the formulae: (See next page.) 



Smithsonian Tables 



