Self shielding

The self-shielding correction has been introduced using the following prescriptions.

For each energy group ("energy bin"), the macroscopic cross section is calculated

where, is the number of nuclei/cm3

in the sample material with density , atomic mass and the total cross section of the group . Note that the units for is 1/cm and the cross section is for the sample material (element). is the Avogadro's number.

Then, for each , in a sample of thickness , it is assumed that the flux within a sample is attenuated according to

plot phi.png

It follows that the average flux for a sample of thickness is

This procedure is applied to each energy group . It is important to note that the the macroscopic cross section must be computed for the elemental material, in which other isotopes could have resonance in the energy group under consideration, therefore reducing the effective flux experienced by the actual isotope to be activated. The given spectrum-averaged cross section (SACS) with this "shielded" flux, is then calculated for any reaction channel under consideration for activation.


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-- AlbertoMengoni - 2021-03-10

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Topic revision: r5 - 2022-02-13 - AlbertoMengoni
 
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