Using usryield to calculate neutron fluence

dear FLUKA expert
here is my input file that is designed to study the fluence of neutrons from a proton beam using usryield to calculate the fluence of 200MEv neutrons in a water phantom in which I have placed a target which allows me to vary the composition and study the variation of the neutron fluence. in this specific case my concern is at the level of the USRYIELD detector. when I choose the franchise study region (avoid and target, or target tumor) I get nothing like fluence but when I leave these box empty, i.e. by default, I get the neutron fluence curve , it is the same for other particles and LET; have I defined my limits incorrectly? could you enlighten me a bit.
thank you in advance
samedi.inp (2.4 KB)


There is a fundamental different behaviour in the USRYIELD card depending if you provide the region or not:

  1. You do not write anything in WHAT(4) and WHAT(5). In this case, FLUKA will take the default values (i.e. -1 and -2 respectively). With this configuration, it will score the yield of the particle emerging from inelastic hadronic interaction.
  2. If you provide the correct region, it will score the particle yield from the region in WHAT(4) to the one in WHAT(5). In flair they are defined as “Reg”-“to Reg”.
    With this implementation, I see a not too unrealistic neutron spectrum (TUMOR->TARGET and TARGET->TUMOR), what is your problem exactly with this configuration?

Ps. are you sure that you are dealing with a tungsten tumor? I would suggest you also to lower the delta ray cut threshold a bit, in case you want to study the damage to the healthy tissue, since now it is at 10 MeV.