Calculation of Transmission and Shielding
When a Substance is placed between a source of photons and an adjacent
point in space, then the original Intensity of photons at the point is
reduced due to interaction of the photons with the atoms of the substance.
Major interactions are Photoelectric Absorbtion, Compton Scattering and Pair
Production. Partial Interaction Coefficients were derived for all
photon interactions and for all elements and for all photon energies of
practical interest, and
are posted on the WWW.
These coefficients are being used in Monte-Carlo
calculations for accurate simulation of the processes in the substance and
the resulting reduction of photon intensity at the point of interest. Such
Monte-Carlo calculations are very cumbersome and require hours of CPU time
on mainframe computers even for simple problems. Therefore, they are useful
only for fundamental studies or in situations where extreme accuracy of the
calculated reduction of intensity is required.
For practical applications, two Total Interaction Coefficients were
defined as combinations of Partial Coefficients: the Attenuation
Coefficient and the Energy Absorption Coefficient. It is these
two coefficients that are being used for the calculation of
Transmission and Shielding of photons.
Transmission calculations deal with the reduction of the original Flux
of photon environments. One common practical problem is the calculation of
the absorbtion of monoenergetic photons by windows of X-ray spectrometers.
Shielding calculations, on the other hand, deal with the reduction of the
original Energy Fluence of photon environments. One common practical
problem is the calculation of dose reduction by shielding materials.
Equations used for rapid hand-calculations or PC-calculations of
transmission and shielding are discussed in two separate paragraphs:
Calculations of Transmission of Photons, and
Traditional Calculations of Shielding.
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Edited on 28 February 2003 - E-mail to the
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