I am trying to run a simulation with I-131 source.
I defined the source with HI-PROPE; RADDECAY and DCYSCORE were accordingly issued.
If I want to define source points (for instance), I would like to use source_newgen.f as well.
A simple input file and source_newgen.f for this problem are attached. Scoring is done using DETECT card and USRBIN with BEAMPART is used for source visualization. But I have some observations after running the simulations:
If I run the simulations with ISOTOPE definition, DETECT card presents I-131 spectra. However, USRBIN scores zeroes. Therefore I am not able to visualize the source.
If the ISOTOPE definition is disabled, and simple BEAM card is used with E = 0.000364, both DETECT scoring and USRBIN scoring works.
Kindly guide me on this difference.
First, let’s run a simulation in semi-analogue mode without a source routine.
Please review this material. The Radioactive Sources lecture from the last FLUKA Radiation Protection topical course is an excellent starting point.
For an easier setup, I recommend using DEFAULTS PRECISIOn.
Ensure the DCYSCORE is configured correctly - misuse often leads to null scoring results.
Pay close attention to the USRBIN mesh. The source is outside (and even pointing further away from) your mesh.
Once this is set up, you will notice that no results are collected when scoring BEAMPART with a radioactive source.
In semi-analogue mode, FLUKA transports the decay products of the parent isotope, not the isotope itself. The decay time is sampled randomly, followed by the random sampling of daughter particles and emitted radiation. As explained in Note 7 of DCYSCORE, we can see this situation as a special case where only decay particles are present.
Checking some FLUKA variables in debug mode, I can only see decay products being transported, and not the parent isotopes. This would explain why BEAMPART scoring is ineffective in this case: the beam particles have already decayed.
The situation differs for photons, which are the primary particles in your second attempt and enter the simulation as they are.
As a quick, practical and easy solution for your purpose, in this case I would suggest simply scoring ALL-PART instead. Even with the radioactive isotope source, this will allow you to see the fluence of decay products (e.g., photons, …). Given your simple setup, it will be straightforward to reconstruct the location of primary particles in space.
As a final note - depending on your simulation needs - you might want to explore the SPECSOUR BEAMSPOT feature. This specialised BEAM definition allows you to define multiple source points (and much more!) without modifying a single line of code. This lecture provides guidance on how to set it up.
Thank you so much for the detailed explanation and reference to the materials.
It really helped. As I tried, I could now run the simulations with expected USRBIN scoring.