Understanding X-ray Attenuation: Determining Absorption Probability and Depth

[RichardOsmond]

Hi all,
using the mass attenuation coefficient and density, one can determine the percentage of X-rays absorbed in a material for a given depth, using the Beer-Lambert Law. e.g. The intensity of a beam of 8 keV X-rays will be reduced by 68% after passing through 70 microns of Silicon. From my understanding, this formula is used to determine the absorption of a beam of X-ray photons. e.g. in the example i just gave, if 1,000 8 keV photons are incident on the surface of the silicon, only 320 will be present after 70 microns. My question is, how do i determine the probability of where a single photon will be absorbed? If there is only a single 8 keV photon incident on the silicon, at which depth will it be absorbed?

Thanks.

 

[Bob S]

The best you can do is plot a probability curve. There are two mass attenuation coefficients, one representing the absorption (removal) of the incident photon, and the other representing the absorption (deposition) of the energy contained in the incident photon, which includes Compton scattered photons, secondary x-rays, etc.

Bob S

[added] See http://physics.nist.gov/PhysRefData/XrayMassCoef/ElemTab/z14.html

For 8 KeV, the two absorption coefficients in silicon are

8.00 KeV 6.468E+01 and 6.313E+01 cm² per gram

 

[RichardOsmond]

Thanks Bob !