Title: Circular of the Bureau of Standards no. 583:
Abstract:A tabulation of attenuation coefficients of X-rays and gamma rays from 0.01 to 100 Mev for 29 materials is presented.A summary of information on the probability of the basic interaction processes of p...A tabulation of attenuation coefficients of X-rays and gamma rays from 0.01 to 100 Mev for 29 materials is presented.A summary of information on the probability of the basic interaction processes of photons with matter and a detailed analysis of experimental and theoretical evidence are included.Present information on the basic processes is ade- quate for many applications; however, improved theory and additional experimental data are needed in certain areas.A comparison of calculated and experimental coefficients points up this need.There is also an appreciable amount of coherent 1 scattering at small angles.The intensity of this radiation scattered within a cone of aperture 0 max can be obtained by integrating numerical data ' on the differential cross section for this purpose.e This was done by Colgate [5], using the numerical f data of Debye [6] and the equations of Franz [7] ; 4 P Kev radiation is roughly 0.06 percent of the ; , intensity absorbed photoelectrically from the | c incident 100-kev radiation., The number of annihilation photons from the | 8absorber that reach the detector will be similarly small in the usual narrow-beam, experiment.As-; suming that all radiation emitted is from 2 quanta annihilation and is isotropic, the number of photons per steradian will be approximately 16 j t percent of the number of pairs produced.The j ; number of photons detected in a solid angle of 0.01 j steradian is only 0.16 percent of the number of ; electron-positron pairs produced in the absorber by the incident radiation. Combination of Attenuation CoefficientsThe probabilities of interaction processes of an !! Xray photon with different atoms of an absorber add up without mutual disturbance, in general.The effect of chemical binding on the interaction of X-rays with valence electrons is exceedingly weak.However, the orderly arrangement of atoms next to one another does influence the total probability of interaction processes to an extent that is quite considerable, expecially in Bragg reflection by crystal lattices, when the momentum transfer from, photon to matter is of the order of the Planck constant divided by the spacing of adjacent atoms.Special situations of this kind are disregarded in the present Circular.Within this approximation, the mass-attenuation I < The total cross section of Franz is too small by a factor of 2 owing to an 1 analytical error.ireRead More