When I inset lam-bias with the parameters you have mentioned, FLUKA runs but does not generate any .fort files. Would you know why this might be?
One more question: I also want to get production of 227Ac. However, low energy neutron cross sections are not available in FLUKA for 226Ra (LOW-MAT) so I think I will have to convolute the neutron spectrum with the cross sections of 227Ac. However, I have had to put a PRT-THR card and set it to a very high energy to cause neutrons to stop immediately upon creation. This is fine to let the simulation run but I will need to get a spectrum to determine the yield of 227Ac. I tried turning off LOW-NEUT but the simulation will not run if I do this. Would you know how I would go about getting the neutron energy spectrum at the front of the target (facing the beam) at the point of creation?
unfortunately I don’t have the same problem as you, the fort files are generated and they are not empty. May you share your (modified) input file, the *flair file, an *err file and an *out file?
Concerning your second question: you need to score the neutron fluence inside your thin target. Then remove the PART-THR card and add a USRTRACK scoring (you should not discard neutrons in the first place as they contribute to activation).
I checked my input again I saw that my LAM-BIAS card was in there twice. Not sure how this happened but it doesn’t seem to make a difference. No error files were created so I can just give you the flair and input proton_20day.inp (3.4 KB) proton_20day.flair (2.6 KB)
Yes I was trying to score the fluence as you will in the input file. I’ve tried excluding the PART-THR but the simulation will not run without it. Would you know a way around this?
I see now what you meant. The reason why your simulation does not start is because in the Run Tab of Flair you have selected the null queue: this only generates the necessary files so they can be used for other cases. You should select the Default queue.
I apologize since before I gave you a misleading reply. Considering that for Ra there are no low energy neutron cross sections available (it is a bit “exotic” as target material), to avoid any crashes you have as option to set a high threshold for neutrons (as you did) and issue a LOW-MAT card for your target material pointing to any available material. This is explained in the manual for the LOW-MAT card (Note 3):
… even in this case the availability of the low-energy neutron cross sections for the materials defined in input is checked. To avoid the run being stopped with an error message, the user should issue a LOW-MAT command for each material for which cross sections are missing, pointing them to any available material.
This should allow you to run in any case but be aware of the limitations of the results
I managed to fix the biasing issues this is all fine now.
I saw this in the manual, but if I put any material the results will probably not be very reliable. What I thought I could do was get the fluence of the neutrons at the point of creation by allowing them to stop and deposit their energy at the point of creation. That way I don’t have to worry about their transport in the material but ill still get the number of neutrons created. Then I can take this fluence and convolute it with the Ac227 cross sections to get a good estimate of the isotope production.
from the manual for PRT-THRES
So I thought if I turned off LOW-NEUT and set the PRT-THRES to the beam energy, this should give me what I want but it returns an error.
Would you have an idea about this?
apologies for the late reply. You need to keep the neutron threshold high (so you kill them as they are generated) and you leave the LOW-NEUT with any material. The LOW-NEUT card in this case is irrelevant for the transport (since you kill neutrons on the spot): it is just used as workaround to avoid a crash due to the fact that FLUKA checks anyway for the availability of low energy neutron cross sections even if the neutron transport threshold is high.
I actually still have an issue. I believe I have done what you explained and the simulation runs fine i.e. RESNUCLE produces an output that makes sense. But, I am still not getting a neutron fluence in my target at the point of creation. proton_neut_10hr_24_sum.lis.txt (42.8 KB) proton_neut_10hr_24_tab.lis.txt (23.9 KB)
I have switched off LOW-NEUT since as you said, I don’t care about transport of neutrons. I assigned natural Barium as the LOW-MAT for radium, but it still hasn’t made a difference. proton_neut_10hr.inp (3.9 KB)
Hi Jason,
your action on the LOW-NEUT card is irrelevant, since the DEFAULTS/PRECISIOn card activates anyway the low energy (<20 MeV) neutron transport.
What matters to inhibit the neutron transport is the PART-THR card, where you put a cutoff of 20 GeV. This way you cannot get a neutron fluence scoring by USRTRACK and USRBDX, since it implies the neutron transport (in the first case the fluence is calculated from the neutron tracklength in the indicated region, while in the second it is calculated by considering the neutrons crossing the indicated region boundary).
To get the neutron yield at their creation point, you should use the EMERGING option of USRYIELD:
USRYIELD 2201 NEUTRON -28 -1 -2
USRYIELD 0.02 0 100 0.5 -0.5 3 &
Thanks a lot Davide and Francesco for you your help.
Just one last question Francesco, you set the range of second quantity dz to -0.5 to 0.5.
I don’t really understand why this would be the case for neutrons?
Being the requested second quantity the particle charge (in units of the elementary charge |e|), you certainly agree that 0 applies to neutrons. Setting the scoring interval as above, the second quantity bin width is 1 (and 0 is the only integer value included), this way there is no need for renormalizing the result by it.
Cheers
