Scoring secondary electrons from ionization of alphas

Dear experts,

I have an alpha particle source of 3 MeV, where the alpha primaries are passing from a Argon volume. I am interested to track all secondary electrons that are created by ionization and record their “end” positions. At further stage, I would like to apply voltages on the top and bottom side of the Argon box and calculate the total number of electrons that arrive at the end plate (parallel plate detector). Could you tell me please if this is possible and how?
When I calculate the energy deposition spectra or look at the mgdraw, only alphas are scored inside the gas volume without seeing the secondary electrons…

Thanks a lot in advance

Best regards


Hello Georgios,

When I calculate the energy deposition spectra or look at the mgdraw, only alphas are scored inside the gas volume without seeing the secondary electrons…

Could you upload your input file as well as your mgdraw.f so we can take a closer look? For completeness: which version of FLUKA were you running?

Thanks in advance,


alphasV.inp (3.3 KB)

Dear expert,

This is the input I am running using FLUKA Version 4-3.3
with the card:
USRBIN 10. ELECTRON -51. 2. 2. 2.elec
USRBIN -2. -2. 0.0 100. 100. 100. &
I am getting no entries for secondary electrons produced in the gas during the passage of alphas…

Best regards


Dear user,

Two closely linked considerations:

  • A mild technical one: i can see your intention when setting the delta-ray transport and especially the production thresholds with the respective EMFCUT cards, but they were ineffective since the concerned thresholds here apply to electron (or positron) projectiles. You instead need to pass a DELTARAY card to set the delta-ray production threshold for alphas (in general for charged hadrons, for muons, and for ions).

  • A major kinematical one: the maximum energy that an alpha particle of E_\alpha= 2 MeV (as in your input) can ever hope to transfer to an electron is (comfortably affording to use the non-relativistic expression like a hooligan, since 2 MeV is much lower than the alpha mass of around 3.727 GeV/c^2):

E_\textrm{e,max} = \frac{4 m_\alpha m_e E_\alpha}{(m_\alpha+m_e)^2}=1.096 \text{ keV}

The lowest thresholds for e- production/transport you can set in FLUKA are of 1 keV. So with FLUKA you will sample delta rays (if you put the DELTARAY card as suggested above) only in the narrow window from 1 keV to 1.096 keV. The situation improves slightly for the initially implied 3 MeV alphas (you’ll get delta rays from 1 keV up to 1.6 keV or so). Needless to say, the aggregate effect of alpha collisions with e- transferring smaller energies (which are much more likely) is accounted for by means of a continuous energy loss along alpha particle steps based on an effective stopping power description, not via explicit production of delta rays.

Thus, if you’re interested in explicit details of the production and transport of lower-energy electrons, FLUKA is not the most adequate tool. You can at most get a reasonable energy deposition map - if from this you want to guess/speculate how many e- are produced for a subsequent treatment, this is your prerogative.

Incidentally, you can get a sense of what you’d be missing by looking e.g. into

With kind regards,


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