Is THERMR data being used by SERPENT for free gas nuclei?

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VivianS
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Is THERMR data being used by SERPENT for free gas nuclei?

Post by VivianS » Sat Mar 13, 2021 7:47 am

Hi everyone,

I'm currently trying to generate my own ACE files for SERPENT (in PyNjoy2016). As a basis, I looked for NJOY inputs generating ACE files for SERPENT. On this matter, I found this post and Riku pointed me to this software. Most importantly, Riku also sent me a Perl script which does that, but I'm not sure I can share that here. Whatever.

What struck me is that none of these use THERMR for nuclei modeled as free gas (they eventually use THERMR for bound scatterers, but that's not the subject here ; I'm only talking about continuous ACEs and not TSL ones). After reading around that, however, it seems logical since the Doppler-broadening pre-processor seems to include Maxwell-Boltzmann distribution for nuclei as free gas, cf. that page.

Still, I'm bothered, because my PENDF files go through THERMR before becoming ACE files. I'm therefore afraid I'm applying twice the same THERMR-type free gas correction (once in THERMR, once in SERPENT pre-processor) and thus obtaining definitely wrong results.

Is it the case? Or maybe THERMR is just adding data that is ultimately not used by SERPENT?

Ana Jambrina
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Re: Is THERMR data being used by SERPENT for free gas nuclei?

Post by Ana Jambrina » Sat Mar 13, 2021 1:59 pm

After ENDF data is been processed by THERMR module, the different thermal materials are handled as reactions. PENDF tape in Files 3 and 6 includes a special set of MT numbers to include free-gas and bound scattering (split into inelastic and elastic components); free gas corresponds with MT = 221.
It is my understanding that Serpent does not process such material reaction and instead uses a target motion approach during (Doppler broadening) pre-processing.
- Ana

VivianS
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Re: Is THERMR data being used by SERPENT for free gas nuclei?

Post by VivianS » Mon Mar 15, 2021 1:04 pm

Thank you very much, Ana!

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