Gamma rays photon attenuation coefficients

Although gamma rays are much less subject to attenuation than alpha and beta particles, a density correction is needed if the density of the sample deviates significantly from the density of the calibration standards. The effect of density on self-absorption for both the standard and the sample is estimated by Eq. (7.2) [x for this purpose is the photon attenuation coefficient in cm /g and x is the sample area density in g/cm. Values for ix in some common materials are listed in Table 2.2 and in its cited reference. If a large set of samples with consistent density is analyzed, it may be possible to prepare radioactivity standards at the same density to avoid the need for correction. Interpolating efficiency values as a function of density is feasible at energies above 0.1 MeV because the effect of minor density difference on counting efficiency is small. 

The attenuation coefficient for a beam of gamma rays is related to the number of gamma rays removed from the beam, either by absorption or scattering. For the Compton effect, the absorption cross section is determined by the energy absorbed by the electron, which is the total collision energy minus the average scattered photon... 

This table gives mass attenuation coefficients for photons for all elements at energies between 1 keV (soft x-rays) and 1 GeV (hard gamma rays). The mass attenuation coefficient i describes the attenuation of radiation as it passes through matter by the relation... 

This is the parameter plotted in Figure 2.2, comparing attenuation and absorption. The attenuation coefficient only expresses the probability that a gamma-ray of a particular energy will interact with the material in question. It takes no account of the fact that as a result of the interaction a photon at a different energy may emerge as a consequence of that interaction. The total absorption coefficient, niust, of course, take into account those incomplete interactions ... 

Bulk chemical composition was determined by X-Ray Fluorescence (XRF) and carbon-sulphur analyses to (i) define the best sample preparation methodology for Po analysis by alpha spectrometry and (ii) estimate the matrix attenuation effect of 46.5 keV gamma photon emissions from Pb by gamma spectrometry using theoretical elemental mass attenuation coefficients from the literature [4],... 

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