## Isotopic Absorption

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ianyounker
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### Isotopic Absorption

I have calculated the fractional absorption within my clad material (FeCrAl) using the -2 reaction. I am trying to get the fractional isotopic absorption within the FeCrAl. I have setup my detector materials the same way the SERPENT manual did. I have also used the proper reaction numbers (positive number such as 102). However, I cannot make sense of the detector output from SERPENT. My output values are larger than the fractional absorption I found for all the FeCrAl. Do the isotopic absorption values from my detectors need to be scaled by a certain value? Any other thoughts or comments?

Thanks

Ian

Jaakko Leppänen
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### Re: Isotopic Absorption

The negative response functions are related to macroscopic and positive response functions to microscopic cross sections. So the value given by the detector for FeCrAl with -2 is multiplied by the atomic density of the material, while the values for Fe with 102, etc. are not. Could this explain the difference?
- Jaakko

ianyounker
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### Re: Isotopic Absorption

I am not sure the atomic density explains the difference. I use the following detector to get the total absorption within the FeCrAl.

det 3 dm FeCrAl dr -2 FeCrAl

For detector 3 I get a value of 0.06621 and I take this number to be the fraction of neutrons absorbed within the FeCrAl. I then set up my detector materials.

mat Al27 1.0 13027.06c 1.0
etc...

And then I setup my isotopic absorption detectors.

det 7 dm FeCrAl dr 102 Al27
etc...

For detector 7 I get a value of 0.0343 and I take this to be the fraction of neutrons absorbed in the FeCrAl through (n,gamma) reactions with Al27. The value for detector 7 and my others detectors like it are too high. It doesn't seem like including the atomic density will solve this problem. Any thoughts as to where I am going wrong?

Jaakko Leppänen
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### Re: Isotopic Absorption

If you are using the default normalization (total loss rate = 1) and there is no neutron leak, then detector 3 should give the fraction of neutrons absorbed in FeCrAl. This is the macroscopic absorption rate.

Detector 7, on the other hand, gives you the microscopic (n,gamma) reaction rate for Al-27 in the same material. This value has no physical significance, but if you multiply it by Al-27 atomic density, you get the corresponding macroscopic reaction rate. What do you get if you take atomic density of Al-27 in FeCrAl from the <input>.out file and multiply the the detector result with that?
- Jaakko

ianyounker
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### Re: Isotopic Absorption

Mistake on my part. Thanks for the help Jaakko!