Dear FLUKA Expert:
I would like to ask a question. The bond energy of chemical bonds in materials is usually in eV, but the electron beam energy set and calculated is above 1keV, or even above 100keV. Can this accurately reflect the transport process of particles in the material?
Looking forward to your answers!
Dear FLUKA Expert:
When particles reach their threshold in FLUKA, their remaining energy is deposited locally at their position. You can lower your thresholds if you want a more spatially-detailed energy deposition, at the cost of CPU time, for example if you are studying very small regions in your geometry where that level of detail is important. In any case, simulation down to eV energies for electrons would be extremely slow, due to the amount of low-energy secondaries created.
This local energy deposition reflects the low-energy part of the particle shower (ionization, Coulomb scattering, photoelectric effect, and so on). Provided the particle range at threshold energy is small compared to the region of interest, this method is fast and the cut-off does not alter the obtained results.
General-purpose radiation transport codes, such as FLUKA, base the interactions of particles on aggregate interaction coefficients (Stopping Power for charged particles, Mass Attenuation Coefficients and Mass Energy-Absorption Coefficients for neutral particles). These coefficients are calculated by averaging over quantum states, any textbook on radiation-matter interaction will give you the details.
Two references of interest:
- Salvat and LLovet: ShieldSquare Captcha
(just the introduction tells the essential, but many details on the approximations in the aggregated interaction coefficents later on)
- Thomson and Kawrakov: Medical Physics - 2011 - Thomson - On the Monte Carlo simulation of electron transport in the sub‐1 keV energy range.pdf (171.4 KB)
This paper makes the clear statement that the approximations for electrons in water below 1 keV energy lead to systematic uncertainties of the results in excess of 5%.
Best regards, Thomas @totto