# How to plot axial distribution of spallation neutron

Dear Fluka experts,

I want to plot the distribution of neutron spallation within my geometry like the picture below. Could someone give me some guidance on how to do like this?

Thanapong

Dear @thanapong

I would suggest to use a USRBIN estimator of NEUTRON fluence covering the relevant section of your geometry. You can set the appropriate longitudinal binning (e.g. 10 cm bins as in your plot) and just leave one bin in X/Y or R/Φ, depending on if you select cartesian or cylindrical binning. You can then plot the 1D projection of this scoring over Z to obtain a curve of neutron fluence vs. depth. Here is an example with some arbitrary dimensions, to be adapted to your problem. Choose R-Φ-Z type for cylindrical bins.

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Dear @atsingan ,

Thank you for your suggestions. I have followed your guide and got this plot. I’m not sure about the results in axes, is the x-axis from the plot represent the value along “z” of my geometry? and in the y-axis what is the meaning and unit of it?

Thanapong

Dear @thanapong

Yes, the horizontal axis of the plot corresponds to the z-axis of the geometry. Having now seen your input, I suspect that what you wanted may have been the radial profile, rather than this. To obtain it, just add an appropriate number of bins in the R dimension and generate the same plot over R.

With this USRBIN card you are scoring neutron fluence, given in units of neutrons/cm2/primary particle (proton). I notice, by the way, that you are defining a proton beam with a 9 cm FWHM; this is much larger than the 2 cm aperture of the beam pipe. You may want to check whether this is what you intended.

On an unrelated topic, there are four bodies with names longer than 8 characters (targetclad, spallclad, outvessel, beamshell). FLUKA truncates these names, as you can see in the input echo in any of the output files (e.g. in *001.out). It would be advisable to shorten them in order to avoid problems.

Furthermore, the USERWEIG card is probably redundant unless you are coupling it with a fluscw.f user routine.

Finally, your USRYIELD scoring will give you an empty result since the two regions (TARGET and fuel) do not share any boundary.

Dear @atsingan

Thank you for your thoughtfulness and sorry for lately reply, It seem like my input have a lot of mistake that I should check and fix it.

I have one question, I confuse the use of USRYIELD card. In my understanding, if I use region to region yielding, neutrons will be scored at surface boundary of the region. Please correct me.

But if I select yield: EMERGING as shown in picture, what position of neutron will be scored? Is it at the interaction or neutron emerging a while then will be scored somewhere in my geometry?