I am currently investigating cosmic ray muon interactions in water. One of the specific areas I am interested in is the decay products from spallation-induced isotopes. My FLUKA input file contains the RADDECAY card in semi-analogue mode (WHAT(1) = 2) to allow the simulation of radioactive decay.
When I simulate muons traversing my geometry (a cylinder of water) I can see the isotopes I am interested in being produced and can also see many of them undergo decay through writing out information about their decay products using the USRDRAW routine. Though many of the isotopes do not seem to decay, or produce decay products in the simulation. For example, ~10% of nitrogen-16 isotopes do not decay and none of the 114 instances of beryllium-11 I see undergo decay/their decay does not produce any secondaries.
I have previously read in another thread that FLUKA does sometimes not contain decay spectrum information for some isotopes. Is this what is causing the discrepancy between the number of isotopes I see and the number of decays that I see? If so, is there a way to add this information into FLUKA so that the decays are simulated?
Indeed you are right, I can confirm that Be-11 decay products are missing from FLUKA (as they are missing from the NNDC database we use as a source).
This can be solved on our side, by explicitly adding the Be-11 decay products in the software. We are in the process of doing so, and will release this patch it as part of the upcoming minor release.
The case of N-16 is different, as decay products are present in the DB. Could you send me your input and mgdraw file, so that I can have a look? (you can also send it via dm if that’s more suitable). Finally, could you elaborate on what you mean by “10% of N-16 do not decay”?
Thanks for looking into this. That’s unfortunate, do you know what the timescale is usually like for minor releases like this? I have considered using a separate simulation just to simulate the Be-11 decays and can start developing this to “plug” the missing Be-11 decays whilst waiting for the FLUKA update. Though if the update is quick I can avoid doing this.
Sure, I’ve attacked my MGDraw file below. There are a few routines in there for writing out information about the decay products and the particles that decay themselves. I’ve also attacked my usrrnc.f file below as I use this to write out when the isotopes I am interested in are created.
By 10% not decaying I mean that I can see, using the usrrnc.f routine, when any unstable isotope is created in the sim and I find that of the N-16 isotopes created, and saved in the usrrnc routine, only ~90% of interact via decay and set the decay interaction flag in the usrdraw routine.
I have tested the decay of Nitrogen-16 starting from an ISOTOPE beam in vacuum and scoring the decay products. I can confirm all is normal on that side.
Concerning your simulation, please also provide the input file, as I wish to reproduce it faithfully. Also, this forum is related to the CERN-distributed version of the code, and I am unable to compile your user routines which are coming from another distribution of the code. Could you convert them and test that they compile under this version of the code before sending them back to me for testing on my side?
You will find a generic conversion script in the (CERN-distributed) fluka folder Fluka/bin/fluka_src_converter.py, or you can use the templates in Fluka/src/user for that.
Finally, regarding the timeframe of the Be-11 patch, we are trying to include it in the next minor release coming in a few weeks, however, further tests are still ongoing and we cannot commit to a date for this patch yet.
Apologies for the primary file (mupage.evt) being compressed, the forum does not allow .evt extensions.
I had previously been using the alternate distribution of FLUKA as I had issues accessing the download for the CERN version. Though this seems to have now been sorted so I have now switched over to using FLUKA-CERN. Here are my converted user routines:
I can confirm that these compile using the fff binary and link using the lfluka binary.
I have just run my input file and primaries file through with FLUKA-CERN and see less of a discrepancy in the number of isotopes vs the number that decay. For example, N-16 now only has 2 missing decays out of 1973 produced isotopes. Though, Li-8 has a slightly larger discrepancy - 1906 produced isotopes vs 1876 decaying isotopes.
Thank you for the information on the timeline for the Be-11 patch. I understand that it would be difficult to commit to an exact date so I appreciate the estimate.
I obtain the same results as you.
In your usrrnc, you are correctly listing all produced radionuclides. However in your mgdraw.f you are listing IARDPR and IZRDPR, which are the A/Z of the precursor.
So in case the precursor decays twice, the fact you only score the precursor instead of all produced nuclides in the chain will lead to some discrepancy. This is for example the case for 16N which can rarely come from 16C.
All missing 16N lines I had as well were related to a 16C precursor
Okay, that makes sense. So the precursor A/Z always represents the isotope at the top of the decay chain? So, in the case of the 16C decay chain, is there a way to identify when the 16N decays, and write out information about where the decay happened, the fact that the decay is a 16N nuclide, and what products it created?
You’ve probably seen from my files that I want to write out decay products (betas, neutrinos and neutrons) of these isotopes, and information about the isotopes themselves so that I can “tag” the decay products to the isotopes that they have come from.
That’s correct, the precursor is the actual residual produced in the prompt part of the simulation. In the decay part, the residuals decays are simulated and decay products are emitted and transported. In case the residual is 16C, you have two ensuing beta decays to 16O.
Concerning your second question : you should see all decays in USRRNC, which is invoked for each individual decay in the chain (whereas USDRAW is invoked once per precursor) so in your usrrnc.f routine, you could include resnuc.inc to gain access to the following variables: ICRES (atomic number of the parent), IBRES (mass number of the parent) and many more (please see the include/resnuc.inc file for the whole list of associated variables).
I am happy to announce that the Be-11 patch has been released today as part of the FLUKA 4.3.2 minor release. You should now be able to see Be-11 radiation products in your simulation