Error in calculation of thermal neutron flux

Dear Expert,

I am trying to generate number of thermal neutron flux received to detector and spectrum using DETECT card.

we used 2.5 MeV neutron source at 50cm distance from the detector and HDPE block (10 cm distance from detector) to convert fast neutrons to thermal neutrons. without adding HDPE block this work properly and we receive the spectrum. But after adding HDPE to code, it is giving errors ( see attached)

I appreciate if anyone can help me to solve this.

Thanks in Advance

Gd2O3_03Feb22.flair (15.7 KB)

Dear @nadeeraBUL2020,
it is somewhat clear from your question what you are trying to achieve. The error you obtain is not an error from the code.

With the geometry configuration that you currently have, once you include the large polyethylene block, particles essentially never reach the regions where you have implemented the USRTRACK and DETECT scorings so the output files with the scored fluence or pulse height spectra are empty or show large deviations.

Please review the geometry of your setup or, if this really corresponds to reality, increase the number of simulated primary histories.

I hope this was helpful.

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