Dear @horvathd,
I’m interested to simulate Ac-225 production from Ra-226 target using photons from an electron beam bombarding a dense target but I’ve has the same problem as reported in this three topics: LOW-MAT could not find user defined MATERIAL and Missing neutron transport cross section and Rhodium filter error.
I tried what you suggest but my results is empty. Is it possible to import the low-energy neutron cross section data base in FLUKA using a routine?
Best regards,
Isabela.
Dear Isabela,
without an input file (and error files if any) it is quite impossible to tell, why you get zero results. Could you share it with us, so we can take a look?
As far as I know there is no option to use external neutron cross section data in FLUKA.
Cheers,
David
Dear Isabela,
I think the main culprit is the prompt cut option on the RADDECAY card. It seems that, it prevents the electronuclear interactions. If I leave it at 0.0, I get non zero results.
However, radium also doesn’t have a low energy neutron cross section in FLUKA.
The high energy electrons would generate neutrons, and thermal neutrons also contribute to the activation. So cutting the neutrons below 20 MeV is questionable.
This means that cross section from another material has to be used for radium, but then the question comes, how meaningful the result would be.
Unfortunately I can’t give you any solution for this problem. Maybe the others have an idea.
Cheers,
David
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Considering the target thickness, of several radiation lengths, photonuclear reactions (by bremsstrahlung photons as anticipated by @isabela.moraes in her first post above) are actually more relevant than electronuclear reactions. Of course, both of them are prevented by the wrong cut applied to prompt electromagnetic particles in the RADDECAY card, as well spotted by @horvathd.
Now, after removing that cut, thanks to the PHOTONUC card (that in the selected form actually activates both electronuclear and photonuclear reactions, as written in the .out file) one should be able to get (gamma,n) reactions generating 225Ra. The latter will eventually decay (as requested per RADDECAY) into 225Ac.
Relying on the above one as the main production mechanism, I think that the possible contribution of neutron re-interactions (that FLUKA cannot properly simulate in radium - and rhodium 
- anyway, as pointed out) can be safely neglected. To this purpose, assuming that you do not care about neutron related effects, you could better DISCARD them.
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I’ve done these changes and it worked!
Thank you a lot!
Isabela.