Strange behaviour simulating a HPGe measurement of uranium contaminated surfaces

Physics Processes, Models and Cross Sections
1

Dear Geant4 users,
I’m simulating the a measurement of 235U contaminated surfaces with an HPGe detector.
For this purpose, I have defined a source volume wich generates gammas at 185.7 keV ( 235 U gamma line) , after simulation I got the attached result.
The peak correspond to 235U, however I don’t understand where the particles detected at the region 500-700 keV comes from.
I’m using the physics list QGSP_BERT_HP recommended for low energy dosimetric applications.

Is there something I’m missing?

image

Thanks a lot for your help.

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The spectrum from 0.5 to 0.7 MeV is due to Ge(n, n’) reactions. There are two prominent peaks at 0.596 MeV (74Ge(n,n’)) and 0.691 MeV (72Ge (n,n’)).

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