Re: [fluka-discuss]: Secondary protons from a scattering clinical proton beam in water and graphite phantoms

From: Francesco Cerutti <>
Date: Fri, 23 Oct 2015 23:43:20 +0200

Dear Ana,

the explanation for your findings looks pretty obvious, logical and
physical: water (H2O) happens to contain 'free' protons as H nuclei (with
'free' I mean not bound to other nucleons inside a heavier nucleus, like
C and O), so the secondary protons you see in that case are the ones put
in motion - without the need for being 'produced' - by nuclear elastic
scattering on H.



Francesco Cerutti
CH-1211 Geneva 23
tel. ++41 22 7678962
fax ++41 22 7668854

On Fri, 23 Oct 2015, Ferreira De Almeida Lourenco, Ana wrote:

> Dear Fluka experts,
> I have simulated in FLUKA a clinical 62 MeV proton scattering beam and I'm studying the
> dose due to secondary protons in a phantom of water and graphite.
> I'm using a USRBIN card to score dose due to primary protons (by scoring BEAMPART) and
> protons (by scoring PROTON). Please find attached the results of the USRBIN card for
> primaries and protons in the water and graphite phantom, where the phantom is at
> position z=184 cm.
> The results show that the contribution from PROTON is significantly different in water
> and graphite. Also, considering that PROTON-BEAMPART = secondary protons, we conclude
> that these difference comes from secondary protons (since the difference from BEAMPART
> is very small).
> Looking at the production cross section for secondary protons from ICRU 63 (graph in
> attachment) it is unrealistic to obtain such a big difference between water and graphite
> for secondary protons. I can't find a logical interpretation that explain these results,
> unless that the cross sections implemented in FLUKA are considerable different from
> those in ICRU 63.
> Why the contribution of sec protons is so different in water and graphite? Could you
> please provide info regarding the nuclear data that is implemented in FLUKA?
> I have also attached the input files for water and graphite.
> Many thanks,
> Ana

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Received on Sat Oct 24 2015 - 01:08:34 CEST

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