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

From: Ferreira De Almeida Lourenco, Ana <>
Date: Sun, 25 Oct 2015 13:04:24 +0000

Dear Francesco and all,

Thank you for your e-mail. I'm aware of the difference in scatter between the materials. For a mono-energetic beam differences in fluence (at equivalent depths) have been reported to be of the order of 1% at the surface which is mainly attributed to the contribution of alpha particles. This is well understood due to the production cross sections of these particles per atomic mass.

However, what I'm getting with these results (when simulating the configuration beam line) is a difference of 20% at the surface at equivalent depths for secondary protons. If this is mainly due to scatter, then you should see this effect for a mono-energetic beam as well and this is not verified.

Many thanks,

De: Francesco Cerutti <>
Enviado: 23 de outubro de 2015 21:43
Para: Ferreira De Almeida Lourenco, Ana
Assunto: Re: [fluka-discuss]: Secondary protons from a scattering clinical proton beam in water and graphite phantoms

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 Sun Oct 25 2015 - 16:26:40 CET

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