Very low neutron yield in Ra–Be simulation using radioactive decay

Physics Processes, Models and Cross Sections
7

Hi Max and Filippo,

Thank you both for your helpful suggestions.

Max - you were absolutely right about the primary energy. I had not set it initially, and the Ra-226 ions were leaving the world volume before decaying. After setting the energy to 0 MeV, the decay chain started working correctly.

I also investigated the decay chain behavior further. By using:

/process/had/rdm/analogueMC false

I am now able to observe the full decay cascade, and I can see multiple alpha particles per event (around 15–20), corresponding to different branches and excited states.

Filippo - thanks a lot for pointing out the limitations of Geant4 for the 9Be(a,n) reaction. I understand now that the lack of differential cross-section data means the neutron energy and angular distributions will not be accurate if I rely purely on Geant4 physics.

For now, I am focusing on correctly simulating the Ra-226 decay and alpha spectrum. As a next step, I plan to:

  1. Implement a basic a + Be setup in Geant4 to understand the interaction.
  2. Then move towards a more realistic approach using external data (as you suggested), possibly using your open-source repository and tools like LISE++.

I will go through your GitHub repository and paper in detail. If I have questions while implementing the isotope card or energy loss model, I will reach out.

Thanks again for your guidance - it clarified several important aspects of the simulation.

Best regards,
Anamika