Strange Isotopic inventory quantities

Hello fluka experts,

I am attempting to calculate the isotopic inventory following the irradiation of a Ra-226 target with 17 MeV protons: proton_10d.inp (3.6 KB)
I have attached my input file, which uses 10 days irradiation time as an example. The results of which can be seen below:


My problem is that I dont understand how the production of 210Pb, 210Bi and 210Po is so high, since the cross sections for these isotopes are very low when compared to others (such as Ra-225 for eg) at this proton energy. Also, I am surprised about how high the proton induced fissions reactions are, but maybe this can be explained with the really high error that can seen for a lot of them.

Any help would be very appreciated.

Dear @jason.tyrrell,

many thanks for your question. I think one of the major problems is that you define a proton beam of 17 MeV (approximately 0.179 GeV/c momentum) with a wide Gaussian momentum spread of 1 GeV/c and thus you see contributions from different proton energies. More likely the momentum spread is far lower, and you can set it to 0 if you do not have more precise information.

On a side note, for your type of problem and for activation calculations you just need EVAPORATION and COALESCENCE (IONSPLIT should be removed with the latest release): MUPHOTON, EMFRAY, IONFLUCT, EMFFLUO, PAIRBREM, PHYSICS(DECAYS), PHYSICS(EM-DISSO), IONBRPAI are superfluous for your case since you have PRECISIOn DEFAULTS as well. ELECTNUC is also not pertinent: it would make sense only if your primary beam is constituted by electrons or positrons.

On a last note, I would introduce some biasing since your target is very thin. If you inspect any output file, you will find at some point a table listing all the properties of the materials in your problem. Under the column “Inelastic scattering length for PROTON at Beam energy” take the value for your target material: in your case this is 52.20 cm for radium and you can divide your target thickness by it to have a feeling of the reduction factor that one should apply to the inelstic interaction length. Now add a LAM-BIAS card as I have done for example here:

In this way the hadronic inelastic interaction length of the (primary) particle is reduced by the multiplying factor |-1.0E-05| (you can see the manual for more details). This should help even if is only approximate as one should also consider the energy loss in the material.

Please give it a go and let me know if something is not clear.
All the best,

6 posts were split to a new topic: Neutron spectrum at creation point