Proton flux to produce neutrons


I’m modelling a proton flux outside a beryllium cylinder and then scoring neutron fluence through an internal surface of the cylinder using USRBDX. I’ve used LAM-BIAS for the protons. The simulation is running successfully but I’m not getting any data for the USRBDX file at the end. Am I setting up the simulation wrong or is it that the process I’m trying to model is too rare?

gcrsource_newgen_v2.f (19.1 KB)
gcr_spectrum.txt (1.9 KB)
be_cyl_gcr.flair (3.1 KB)



Dear Emma,

I’m getting a spectrum without any issue, even without biasing.

When you process the data, make sure your scoring is in the list of Detectors.


Hi David

In Flair, under the ‘Data’ tab I have the be_cyl_gcr_50.bnn file listed, but when I try to process I get the following error:

Started 2024.04.22 13:14:34

WARNING: No input data found for ‘be_cyl_gcr_50.bnn’
Error processing: be_cyl_gcr_50.bnn
Ended: 2024.04.22 13:14:34

Possible errors: be_cyl_gcr_50.bnn
Correctly processed:



Dear Emma,

the only scoring in the input file you uploaded is for unit 21. The Data tab may show the old scoring you used to have.

To add the current ones to the list you can use the Scan button. And with the Remove button you can delete the ones which are no longer present.