Dear Antara Sehili ,

It's hard to fully replicate real background conditions, especially for:

Scattered radiation from complex room geometries.

Time-varying background (e.g., radon progeny).

Secondary radiation from cosmic rays (e.g., muon-induced events, neutron activation).

Radon and short-lived daughters, often major indoor contributors, are hard to simulate unless their concentration is known and modeled explicitly.

Natural background sources (K-40, U/Th series) are typically due to radioisotopes in walls, floor, air, and surrounding materials. The goal is to reproduce their gamma emissions as observed experimentally. You need some real data to be able to implement this, which increases the burden and computational time.

The Cosmic-ray background (from muon secondaries, neutron capture, etc.) can be approximated by a broad energy spectrum source irradiating the detector from the top or surroundings. You can get this from a prior simulation or using various MC tools like PARMA.

Environmental surfaces/volumes as sources: If you have dose-rate measurements or spectrometric data for specific room materials (e.g., concrete), you can define volume sources in corresponding geometry cells (e.g., walls, floor, roof/ceiling, …).

However, a practical workaround I often apply in Monte Carlo simulations is to account for experimental background, such as natural environmental radiation, by adding it to the simulated spectrum during post-processing. Other types of background, such as from radioactive samples or target materials, can typically be modeled directly within the simulation geometry.

Dear Guembou Shouop Cébastien Joël ,

Thank you for your detailed and insightful response.

I would like to clarify one point further: If I simulate only the gamma radiation coming from the samples or nearby sources present in the laboratory (e.g., calibration sources or activated samples), can I expect the resulting spectrum to be sufficiently comparable to the experimental background spectrum?

Or, should I explicitly add gamma-emitting radionuclides such as K-40 and the U/Th decay series (e.g., Bi-214, Pb-214, Ac-228, Tl-208, etc.) as additional sources in the simulation to better reproduce the full environmental background?

I want to ensure that the simulated spectrum reflects the actual lab background as closely as possible, particularly for low-count regions.

Looking forward to your advice. Best regards, Antara SEHILI

Dear Antara Sehili ,

There is no direct answer, especially if you are in a high background area resulting from the radioactivity of building materials. Perhaps your simulation won't have a peak around the 1460 keV of 40K or other radionuclides in the background.

If the gamma radiation coming from the samples or nearby sources present in the laboratory (e.g., calibration sources or activated samples) is too high compared to the environmental background due to other factors (building, cosmic, and telluric), then you can assume your simulation is representative of the real situation.

This depends on your purpose in implementing such detailed simulations.

If your intention is only to compare both spectra (experimental and the MC ones), then you need to implement a full simulation with those details, or just add the background spectra to the detector in your simulation!

Hope this helps!

Best!

Dear Guembou Shouop Cébastien Joël ,

Thank you very much for your detailed explanation and helpful insights. it helped clarify how far I need to go in modeling the background depending on my objective.

Best regards, Antara SEHILI