Re: Energy deposition in Argon... strange feature??

Dear Georgios,

good question! (if you still remember it)

After a bit of fascinating investigations together with Alberto and
Alfredo, we ended up with realizing that the shoulder you reported (indeed
at ~6keV) has a physical meaning, since it is due to the collision of the
primary electron with an electron of the argon atom K-shell, that has a
binding energy of 3.2keV. (By chance, ~3keV is also the most probable
energy loss of 500MeV electrons in a 1.5cm argon layer, as indicated by
the main peak). So this binding energy amount is additionally spent in setting
free the K-electron, and you find it deposited in the gas. What happens in
reality is that the K-vacancy is filled through the emission of a
fluorescence photon or an Auger electron, with a quite different effect on
energy deposition in a gas due to the respective range. This process is
not (yet) explicitly simulated in FLUKA (i.e. the fluorescence
photon/Auger electron is not generated at all), but, since the
K-fluorescence in argon should have a probability lower by one order of
magnitude with respect to Auger emission, the K-shell binding energy is in
fact deposited in the gas in most cases.

All the best

Francesco

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From: Georgios Tsiledakis
Date: Fri, 2 Jul 2010 12:39:22 +0200

Dear FLUKA experts,

      I wonder whether u can have a look at the attached picture.
I have a thin window 100cm x 100cm x 1.5cm of gas volume Argon at 1 atm.
I hit with an electron source of 500 MeV from distance of 50 cm vertical
in the centre that gas window.
The energy deposition is given in the attached plot.
the maximum is around 2.8 keV probably the mip energy BUT there is
a shoulder around 8 keV (??)
I shitch off some fluka procedures BUT in vein...
I search at experimental data too but nothing comes out...

Is it any physics for that?

thank you very much in advance

Best regards

Georgios

**************************************************
Francesco Cerutti
CERN-EN/STI
CH-1211 Geneva 23
Switzerland
tel. ++41 22 7678962
fax ++41 22 7668854
Received on Thu Aug 19 2010 - 18:51:02 CEST