I have specifed a very simple geometry where the CR particles are generated from a certain radius using the GCR-SPE and SPECSOUR card. Next, I have defined a USRBDX card to score the fluence between two concentric sphere regions. I did not specify the area of the detector (so by default it should be 1cm^2). After simulation, when I looked into the sum.lis file for the detector, the area of detector is some large figure other than 1. To test further, I specified the area of the boundary crossing surface(i.e - the detector area). Again, the sum.lis file shows ’ the Area of the detector’ as a figure different from what I have specified. Is there any scenario when this happens or am I going about this in a misguided way?
You would need to use the option NO-NORM to avoid FLUKA trying to apply the normalization factors for the Earth atmosphere’s model. What you see in the output is a pre-computed normalization factor. When using the NO-NORM option, your area will be equal to 1 (or whatever value you set in your *.inp file).