We have noticed that the production of elements, through the photonuclear interaction has changed going from version 4.0.1 to version 4.1.1
In our simulations, we irradiate a target using a 75MeV electron-beam. We are then interested in the bremsstrahlung mediated photonuclear effects which turn Mo-100 into Mo-99.
I have run the same input file (Mo_activation.inp (4.1 KB)) on both version 4.0.1 as on 4.1.1, and I see a marked increase in activation; on the order of a 26% yield increase for Mo99. This behaviour also persists in version 4.2.
Benchmark real-world experiments we have done agreed with the case as calculated in the joint INFN-CERN Fluka version FLUKA 2011 2x.6, and stayed consistent with 4.0.1. I also found this forum post on a similar issue regarding Fluka versions and photonuclear interactions: Photonuclear reactions
To be certain of our results, also in other simulations, we would really like to know the root cause of this effect. Is this caused by a change in cross-sections, or in changes to certain physical processes? And which version constitutes the right results?
There was no change in the relevant cross sections (Bremsstrahlung emission or subsequent photonuclear reaction cross section) for your problem.
or in changes to certain physical processes?
Yes, as discussed in the post you appropriately refer to, what changed between versions 4.0.1 and 4.1.1 was the inclusion of an account of spin and parity in the evaporation stage of the nuclear reaction model.
In your case you are sensitive to 100Mo(g,n). I took the liberty of examining the cross section for 100Mo(g,n) obtained with FLUKA 4.0.1 and 4.2, displayed here along with the few experimental points one gathers from EXFOR:
The effect is analogous to that exhibited in the aforementioned post.
which version constitutes the right results?
Versions from 4.1.1 on contain richer physics than those before, as it’s normally the case for the latest release, which is the recommended one. Moreover, the previous post indicates that new results are in better agreement with available data.
In your case you are of course probing a continuum of photon energies extending up to ~75 MeV. Would you mind sharing more details of your experimental procedure/setup/results in order to investigate the agreement worsening you report wrt your data?
With regards to this issue and the 255-Ra post it might be beneficial to consider the timeline of FLUKA and possible modifications:
V2020, includes spin+parity corrections?
V4.0, no spin+parity corrections thus smaller cross-sections
v4.1, spin+parity corrections included
The post seems to indicate that the results in V2020 were in better agreement with available data.
To the extent that I have measured data to compare, Fluka 2020 seems closer to the truth.
Or was your comment regarding “new results” concerning the v4.1 results?
The cross-sections on 225-Ra shows a decrease going from V2020 to V4. Is this because spin+parity was taken into account in the 2020 version?
As we have seen no difference between the joint Fluka-2011 version and v4.0, does this mean Fluka-2011 also didnt take into account spin+parity, and this was added to a later version V2020?
I hope to get back to you on the issue of experimental data.
This forum provides support for FLUKA v4 distributed by CERN.
does this mean Fluka-2011 didnt take into account spin+parity?
v4.0, no spin+parity corrections thus smaller cross-sections
v4.1, spin+parity corrections included
Yes, these are all true statements. With spin/parity considerations, the cross section for (g,n) generally increases in detriment of (g,2n) at the onset of the latter.
Was your comment regarding “new results” concerning the v4.1 results?
Indeed, in my previous reply “new results” implied v4.1, whose increased (g,n) cross sections better match expectations as indicated by Carl in the aforementioned forum post.
