I am simulating a stacked foil geometry irradiated by a 17.5 MeV alpha beam in FLUKA. The setup consists of several thin foils arranged sequentially, and I would like to evaluate the energy degradation of the beam through the stack.
Specifically, I would like to determine:
The energy of the alpha particles entering each foil
The energy of the alpha particles exiting each foil
The resulting energy loss per foil
Could you please advise on the most appropriate FLUKA scoring strategy to obtain these quantities?
Thank you in advance.
Input files
Please upload all relevant files. (FLUKA input file, Flair project file, user routines, and data files)
Different approaches can be followed to obtain the quantity of interest:
Score, by means of USRBDX cards, the alpha spectrum differential in energy for each boundary crossing in the geometry, i.e. at the interface between two different thin foils. From the scored spectrum, the average energy loss of alphas in a foil can be evaluated by first calculating the mean energy at the entrance and at the exit of the foil (equal to the integral of the particle energy multiplied by the scored energy spectrum, normalized to the total number of particles), and then subtracting the two quantities.This approach is the simplest and requires the least scripting effort.
A second approach uses similar scoring, but implemented through the BXDRAW entry of the mgdraw.f user routine. This entry is called every time a particle crosses a boundary, and from within the user routine it is straightforward to access the properties of the currently tracked particle. In this way, you can check, for each alpha particle, its energy at the entrance and at the exit of the foil and directly score the corresponding energy loss. I recommend checking the course lesson on mgdraw and, more generally, the lesson on user routines from the advanced course if you choose to follow this approach.
Independently of the approach used, given the geometry composed of thin foils, I additionally suggest following the recommendations described in the advanced settings lesson, particularly the use of FLUKAFIX (see the manual page). This card can be used to set a maximum particle step in the geometry materials as a function of the maximum fraction of kinetic energy that the particle is allowed to lose through dE/dx along a step. Not using this card may lead to simulation artefacts, as showed in the mentioned lesson.