Re: [fluka-discuss]: Gas ionization by 400 GeV proton beam

From: Anna Ferrari <>
Date: Tue, 22 Apr 2014 03:37:14 +0200

Dear Silvia,

the assumptions you made in your first estimation are reasonable... to go
further you cannot use FLUKA: you know already that the electron transport
threshold can be set down to 1 keV but not below, and there are no specific
features in FLUKA (as far as I know) that can help in your estimation.
I think that you have now to take into account the fraction of energy that
goes in excitation and the fraction that goes in ionization, and you have to
know for your rubidium gas the energy needed to produce an ion pair.

Thanks to Alberto Fasso', I put here some literature that maybe can be useful
for you (for sure you have already papers...):
- Larson 1958, Phys. Rev. 112, 1927
Values of w for protons in A, N2, CO2, dry air, and "tissue-equivalent" gas
were measured as 26.66±0.26, 36.68±0.34, 34.37±0.33, 35.18±0.42, and
30.03±0.29 ev/ion pair, respectively.
Average Ionization Energy (IE eV) per Pair of Some Common Substances
Material Air Xe He NH3 Ge crystal
Average IE 35 22 43 39 2.9
- J M Valentine and S C Curran, Average energy expenditure per ion pair in
gases and gas mixtures, Reports on Progress in Physics, 21, 1 (1958)
Theoretical and experimental work on the evaluation of w, the average energy
expenditure per ion pair, in various gases and gas mixtures is reviewed.
Ionization by electrons, α-particles, protons and heavy particles is

Hope it helps,
kind regards,

Am Thu, 17 Apr 2014 07:07:09 +0000 schrieb Silvia Cipiccia
> Dear FLUKA experts,
> I'm trying to estimate the ionization produced by 400 GeV proton beam in a
>low density (1.4e-7 g/cm^3) rubidium vapour cell 10 m long.
> What I have obtained is an energy loss by ionization of the order of 2e-7
>GeV per proton in 10m which is in good agreement with what I obtain from
>analytical calculations using Bethe Formula.
> I would like at this point to do a further step to estimate the number of
>electrons that are freed. As a first estimation I could assume that all the
>energy deposited as ionization goes to free the outer electrons (~ 4eV).
>However, I'm not sure up to which extent this is correct. Is there any
>feature in FLUKA which can help me in this estimation, or do you have any
>suggestion of some software/tool that I could use?
> Many thanks
> Silvia Cipiccia
> 6.06 Colville Building
> Physics Department
> Strathclyde University
> Glasgow

Anna Ferrari
Institute of Radiation Physics
Helmholtz-Zentrum Dresden-Rossendorf e.V.
Tel. +49 351 260 2872

Vorstand: Prof. Dr. Dr. h. c. Roland Sauerbrey, Prof. Dr. Dr. h. c. Peter
Vereinsregister: VR 1693 beim Amtsgericht Dresden
Received on Tue Apr 22 2014 - 04:45:38 CEST

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