Dear Ana,
I apologize since in my explanation I did not mention an essential piece
of information and eventually I concluded my last reply with a wrong
statement, affirming that the secondary proton effect in water was there
also with a mono-energetic beam. This is not true, as you correctly
reported, and the reason is that this effect is indeed due to recoiling H
nuclei put in motion by nuclear elastic scattering - as I previously
pointed out -, but the latter is induced by neutrons generated in your
beam line material and not by beam particles. In fact, if in your
simulation you discard neutrons, the extended contribution of secondary
protons disappears.
Best regards
Francesco
**************************************************
Francesco Cerutti
CERN-EN/STI
CH-1211 Geneva 23
Switzerland
tel. ++41 22 7678962
fax ++41 22 7668854
On Sun, 25 Oct 2015, Ferreira De Almeida Lourenco, Ana wrote:
> Dear Francesco and all,
>
> Thank you for your e-mail. I understand your point, however I don't see the same effect for a mono-energetic beam. Please find attached the results of the USRBIN card for PROTON in the water and graphite phantom, where the phantom is at position z=0 cm, for a mono-energetic beam of 60 MeV. I don't understand why I don't see the same effect for these simulations.
>
> Many thanks,
> Ana
> ________________________________________
> De: Francesco Cerutti <Francesco.Cerutti_at_cern.ch>
> Enviado: 25 de outubro de 2015 15:13
> Para: Ferreira De Almeida Lourenco, Ana
> Cc: fluka-discuss_at_fluka.org
> Assunto: Re: [fluka-discuss]: Secondary protons from a scattering clinical proton beam in water and graphite phantoms
>
> Dear Ana,
>
> I think you missed the point. The secondary proton difference you observe
> with water is not due to scattered beam particles (nor to proton
> production in non-elastic reactions), rather to recoiling H nuclei (from
> nuclear elastic events), which are protons as well and in graphite do not
> exist. Of course you get them also with a mono-energetic beam.
>
> Kind regards
>
> Francesco
>
> **************************************************
> Francesco Cerutti
> CERN-EN/STI
> CH-1211 Geneva 23
> Switzerland
> tel. ++41 22 7678962
> fax ++41 22 7668854
>
> On Sun, 25 Oct 2015, Ferreira De Almeida Lourenco, Ana wrote:
>
>> 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,
>> Ana
>>
>> ________________________________________
>> De: Francesco Cerutti <Francesco.Cerutti_at_cern.ch>
>> Enviado: 23 de outubro de 2015 21:43
>> Para: Ferreira De Almeida Lourenco, Ana
>> Cc: fluka-discuss_at_fluka.org
>> 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.
>>
>> Cheers
>>
>> Francesco
>>
>> **************************************************
>> Francesco Cerutti
>> CERN-EN/STI
>> CH-1211 Geneva 23
>> Switzerland
>> 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 - 22:01:36 CET