Re: Re: [fluka-discuss]: what is the meaning of Mean Excitation Energy

From: Fasso, Alberto <fasso_at_slac.stanford.edu>
Date: Fri, 11 Sep 2015 16:29:39 +0000

The mean excitation energy (or mean excitation potential) is a quantity appearing

in the Bethe-Bloch formula for stopping power. Look at the Wikipedia article on

"Bethe formula".

The value for Ar is indeed 188 eV, as you can check on many databases, for instance on http://physics.nist.gov/PhysRefData/XrayMassCoef/tab1.html

To understand its physical meaning, look at http://pdg.lbl.gov/2014/AtomicNuclearProperties/adndt.pdf :

"The electronic stopping power is calculated by summing the contributions of all possible inelastic scatterings. These are normally from lower to higher (bound or unbound) electronic energy states, so the particle loses a small amount of energy in each scattering."

A simplified expression for the mean excitation energy I is given by:

               In(I)=Integral(df/dE lnE dE) /Integral(df/dE dE)

where df/dE is the density of optical dipole oscillator strength f per unit
energy of excitation E above the ground state and the integrals include summations over the discrete states. ?
(See http://www.osti.gov/scitech/servlets/purl/6733705-roWoV2/? )


Alberto


________________________________
From: owner-fluka-discuss_at_mi.infn.it <owner-fluka-discuss_at_mi.infn.it> on behalf of YANG Tao <yangt_at_ihep.ac.cn>
Sent: Friday, September 11, 2015 5:54 AM
To: Mikhail Polkovnikov <Михаил Полковников>
Cc: fluka-discuss_at_fluka.org
Subject: Re: Re: [fluka-discuss]: what is the meaning of Mean Excitation Energy

Dear Mikhail,
Thanks for your answer. But what is the mean excitation energy? Is it the average value of all the excitation energies? And what's its relation with the physical quantity--- "the average energy expenditure per ion pair"?

regards,
Tao Yang

-----????-----
???: "Mikhail Polkovnikov <Михаил Полковников>" <pmk_at_ihep.ru>
????: 2015?9?11? ???
???: "YANG Tao" <yangt_at_ihep.ac.cn>, "fluka-discuss_at_fluka.org" <fluka-discuss_at_fluka.org>
??:
??: Re: [fluka-discuss]: what is the meaning of Mean Excitation Energy

On 11.09.2015 13:22, YANG Tao wrote:
Hi, everyone!

When I look the output(.out) of FLUKA, I find that the mean excitation energy of Ar is 188 eV, but the excitation energy of Ar is 15.7 eV which can be found anywhere. I try to find the definition of the mean excitation energy, unfortunately, I cannot find it. Could anyone can tell me the meaning of the two physical quantities?


regards,

Tao Yang



Dear Tao Yang,

The energy 15.7 eV is the least bond energy for upper shell electron (http://xdb.lbl.gov/Section1/Table_1-1.pdf)


Best regards,
Mikhail

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Received on Fri Sep 11 2015 - 20:07:11 CEST

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