Dear Davide Bozzato
The target materials is PbBi and the Pb contain four isotopes of lead (204,206,207 and 208). I have defined the materials card with all the four isotopes, I am not sure if i define it correctly and also compound materials. Kindly help me to have a look.
Thanks in advance.
example.inp (2.5 KB)
Dear Davide Bozzato
You are correctly using the MATERIAL card to define the isotopes. Note however that you must respect the spacing of 10 characters between the WHATs of a card in the input file. In addition, floating point numbers must end on the 10th character column of the WHAT. A valid way to define the isotopes in the input file would be:
MATERIAL 82. 203.9730 11.34 10. 204-PB MATERIAL 82. 205.9745 11.34 11. 206-PB MATERIAL 82. 206.9759 11.34 12. 207-PB MATERIAL 82. 207.9767 11.34 13. 208-PB MATERIAL 83. 208.9804 9.78 14. BISMUTH
Note that I also fixed a probable typo with the naming of 207-PB. I suggest you use the Flair software to edit the input file. Flair is very convenient as it identifies alignment errors as well as other inconsistencies (see Official flair site for details). That said, if you wish to use natural lead for your PbBi compound rather than using a specific isotopic composition, I recommend you use the built-in lead by using the material name “LEAD” when defining your compound.
Otherwise, if your BiPb compound must be of a specific isotopic composition, then I suggest you first create this variant of LEAD as a compound. Using the molar fraction it could look like:
COMPOUND 1.4 204-PB 24.1 206-PB 22.1 207-PB MYLEAD COMPOUND 52.4 208-PB
For such user defined material, I also recommend that you use the LOW-MAT card to set the correspondence between a material and low-energy neutron cross sections:
LOW-MAT MYLEAD 0.0 0.0 0.0 0.0 0.0 LEAD
The WHATs 2/3/4 are identifiers of the neutron cross section data that you which to use. Refer to Section 10.4.1.2 of the Fluka manual for the full list of available datasets (10.4.1.2} List of materials for which cross sections are available in the | FLUKA). More information about the LOW-MAT card can be found in the Fluka manual or in this forum.
Be careful, there are some fundamental misconceptions in the exchange above.
Both in @profftee97’s input and in @blefebvre MATERIAL cards, no single lead isotope is defined at all, rather for all of them the natural composition is taken by FLUKA! This is because the isotope selection is made by WHAT(6) (mass number - integer given as real, e.g. 208.0 - of the material, as in the manual) that you left blank (implicitly asking for natural composition). As for WHAT(2), leave it blank, as the manual clearly states (NOT to be filled). The respective atomic weights (that are different from the mass numbers) will be correctly set by FLUKA automatically. Moreover, please leave blank the material index too (again NOT to be filled in case of name-based input, see the manual).
Then, LOW-MAT cards do not apply to compound materials, since low energy neutron cross sections are defined for their elemental components.
Finally, the FLUKA library contains low energy neutron cross sections only for the natural lead composition and for 208Pb. So, as far as low energy neutron transport in your lead material is concerned, you have only these options, irrespective of your own defined isotope composition. If you care about nucleus production by 100 MeV protons on a (thin) lead target of specific composition, the aforementioned unavailability is not a critical showstopper, though.
Thanks. I hope I can start my WHAT 4 number from 26 27 28. 29 instead of 10 11 12 13 since FLUKA built materials number stop at 25 and retain bismuth number as the one in the FLUKA built in materials.
What do you suggest I should do. The target is compound materials Lead-Bismuth. The lead consists of four isotopes.
There is no bismuth among the 25 FLUKA pre-defined materials. And there are no single lead isotopes. So, once you define them, they will take automatically a number from 26 onward. Conversely, if you redefine a pre-defined material (using the same name as in the manual), this will keep the original number. In any case, leave the respective field empty.
You can check the name-index correspondence in the output file.
I suggest to do something that makes sense as a function of your goals.
I understand that you are interested in neutron production on your lead-bismuth target. Then, neutron transport in the latter may not be a main issue, as I commented above at the end of my first post.
Define (properly, see above) your target isotope composition, such as the incoming proton will react on a target isotope correctly sampled by FLUKA. Assign to each mono-isotopic lead material (by means of the LOW-MAT card) the low energy neutron cross sections of the lead natural composition (this obviously is not correct, but it allows the produced neutrons to be transported below 20 MeV in the target). Score neutron double differential distributions by means of USRYIELD/EMERGING (see the manual and a fresh post). If you (really) need more, use mgdraw.f, but not the BXDRAW entry, rather the USDRAW entry (allowing to access the reaction products right after the reaction took place). Also, you may need to bias proton reactions by means of the LAM-BIAS/INEPRI card (in this case, statistical weights WEI (IP) become crucial in your USDRAW customized scoring, while they are automatically taken into account in the case of built-in USRYIELD scoring).
Thank you for your explanation. It will help alot.
Based on your suggestion, I defined the materials card for each isotope with low materials card. I also add Usryield/emerging card. Kindly help me to have a look. I am still a beginner struggle to understand all the fluka concept.
Final.flair (2.6 KB) Final.inp (3.1 KB)
Please remove the WHAT(4) (#) and WHAT(5) (dE/dx) content from your MATERIAL cards.
You forgot to assign the PbBi name to the COMPOUND card defining it.
You forgot to select the component names in the COMPOUND card defining LEAD.
Remove the USERDUMP card from your input, not to get a huge useless output.
In the USRYIELD card, select Log, put 130 as Nbins1 (i.e. 10 per decade, which applies above 20 MeV only), =pi as Max2 and d2N/dx1dx2 as Kind.
Leave WHAT(5) (dE/dx) blank in the PbBi MATERIAL card.
I’d have selected in all LOW-MAT the cross sections of natural lead, rather than 208Pb, but it may be not so critical to your purposes, as discussed above. Nevertheless, the LOW-MAT cards are wrong, because each of them should refer to one of your single isotope lead materials (204-PB to 208-PB), and not to the LEAD compound (LOW-MAT cards do not apply to compounds).
Last, I’d bias the proton reactions in PbBi by means of the aforementioned LAM-BIAS card.
Thank you so much for your assistant. Have corrected the Low-Mat accordingly and also use natural lead cross sections. I need to read more on LAM-BIAS card and include it later in the day.Final.flair (2.6 KB) Final.inp (3.1 KB)
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