Dear @zavier.ndum.ndum,
Sorry for the late response.
The DETECT card will register each event and place them in the histogram according to their energy. It’s possible that an event results in no energy deposition, and you are free to handle these events as appropriate for your case study (for instance, using E_min > 0).
The USRBIN card records energy deposition, and by definition, it does not account for events that do not deposit energy as explained here. My personal advice would be to always use the most appropriate FLUKA card for your goal. In your case, if you want to know the energy deposition in your element, I recommend using USRBIN.
This statement is wrong:
I choose this approach because I think that the first bin will always differ in energy width, depending on the E_max and so, setting E_min = 0
All energy bins will be equally spaced. However, if you set a very small value for E_min, the output may not display the exact bin edges due to rounding errors. To avoid this, you can set a DETECT card in coincidence mode, using the detector region as the trigger, while setting E_min = 0 and using the previous low value for E_cut.
Cheers,
Samuel