694 



TABLE 



765.— MASS-ABSORPTION COEFFICIENTS FOR A NUMBER 

 MATERIALS FOR DIFFERENT WAVELENGTHS* 



OF 



Wavelength 

 angstroms 



.010 

 .015 

 .020 

 .025 

 .030 

 .040 

 .050 

 .064 

 .072 

 .098 

 .130 

 .175 

 .200 

 .280 

 .417 

 .497 

 .631 

 .710 



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



TABLE 766.— EXPONENTIAL FORMULAE FOR THE TOTAL MASS-ABSORP- 

 TION VALUES, fi/ P , FOR SEVERAL ELEMENTS* 



Absorber 



Mo . 

 Mn 



Ag . 

 Ag . 



Pb . 



X(/0 

 .1 to .35 



.1 to .4 



v-lp 

 450 X X 3 + .4 

 51.5 X X 3 + 1.0 



603 X X 3 + -7 

 86 X X s + .6 



510 XX 3 + .75 



For reference, see footnote 236, p. 692. 



TABLE 766A.— X-RAY DOSAGE UNITS 



The international unit of quantity or dose of X-rays (and gamma-rays), one roentgen, 

 r, is obtained from that X-ray (or gamma-ray) energy which, when the secondary electrons 

 are fully utilized and secondary radiation from the walls of the chamber avoided, under 

 standard conditions 0°C and 760 mmHg, produces in a cubic centimeter of atmospheric 

 air such a degree of conductivity that the quantity of electricity, measured at saturation, 

 equals 1 esu. 



TABLE 767.— PROTECTIVE POWERS OF MATERIALS RELATIVE TO LEAD* 



A lead screen is very effective in protecting against X-rays. The data in the table show 

 the thickness of lead is as effective as 1 mm of certain other materials that are in common 

 use for protection against X-rays generated by a 100,000-volt Coolidge tube. 



Lead glass 12 to .20 



Lead rubber 25 to .45 



Bricks and concrete 01 



Woods 001 



Barium sulfate plaster 05 to .13 



Steel 15 



For reference, see footnote 236, p. 692. 



SMITHSONIAN PHYSICAL TABLES 



