I want to study radiation shielding after 3 MeV protons hit a lithium target, using the precision mode. I have scored the total dose, neutron dose, and gamma dose. The result shows that the gamma dose is 0, and the total dose is almost equal to the neutron dose. I am using FLUKA version 4-4.1. Is there something wrong with the physics and transport settings?
In addition to dose, score also photon and neutron fluence in the region of interest, to characterize the radiation field. Also, consider that most of the protons will not generate any neutron/gamma, so you may need to bias proton nuclear reactions (by LAM-BIAS) to attain statistical significance.
Thank you for your suggestion. And I also try to open the Low-pwxs card, the prompt radiation display shows gamma now.
With DEFAULTS/PRECISIO, pointwise low energy neutron treatment and related gamma production are already activated, with no need in principle to add the LOW-PWXS card.
Thank you for your reminder. Is it effective to use EMFCUT and LOW-BIAS to reduce the transport threshold for photons, positrons, electrons, and neutrons? In the attached out file, it can be seen that inelastic interactions have produced photons, but the photon dose is still not visible.
job23001.out (508.4 KB)
I scored the gamma spectrum in the vacuum near the target, and the result was 0. I am a bit puzzled as to why the secondary particles produced by inelastic scattering show gamma rays, but the gamma spectrum in the vacuum near the target is 0.
Kindly guide me what is happening? Why is the transport threshold energy for electrons and photons in the out file so high, reaching tens of MeV? I attempted to reduce the transport threshold using the EMFCUT card, but it seems to have little effect. Could there be a mistake in the settings?
Forget about LOW-BIAS that applies to the old groupwise low-energy neutron treatment.
Also, default PRECISIO thresholds for EM particles, namely 33 keV for photons, may not require further adjustment by EMFCUT.
The problem comes from the (pointless) use of RADDECAY, where - through the fifth input field - you raise the EM thresholds so as to disable the prompt EM transport.
I guess that your shielding study concerns prompt dose, during proton irradiation. RADDECAY and associated cards (IRRPROFI, DCYTIMES and DCYSCORE) are meant for decay radiation (that does not include neutrons, by the way), due to delayed radioisotope decay in the absence of irradiation, and should then be removed.
I need to study both the prompt radiation during proton irradiation and the induced radioactivity of the facility. Is it not possible to obtain prompt radiation and the decay of induced radioactive isotopes from the same case?
Of course it is, but for this purpose you should not kill the prompt EM radiation in the RADDECAY card, avoiding to rescale there the respective transport thresholds (leave WHAT(5) empty).
Thank you for your patient and detailed answers. You have been of great help to me.
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