Re: [fluka-discuss]: Attenuation coefficient for photons in a material

From: Fasso, Alberto <fasso_at_slac.stanford.edu>
Date: Fri, 16 Feb 2018 16:03:30 +0000

Dear Beatrice,
the easiest way to calculate the linear attenuation coefficient is to score the flux of
primary particles (BEAMPART). This avoids the buildup due to scattered particles.

Alberto
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From: Beatrice Pomaro <beatrice.pomaro_at_dicea.unipd.it>
Sent: Thursday, February 15, 2018 4:53 PM
To: Fasso, Alberto
Cc: Mauro Valente; Vasilis Vlachoudis; fluka-discuss; owner-fluka-discuss_at_mi.infn.it
Subject: Re: [fluka-discuss]: Attenuation coefficient for photons in a material

Ok, thank you very much Dr. Fass. Does it mean that I have to correct the computation with a buildup factor coming from literature for the absorbing medium (and keep the ratio of the fluxes given by Fluka) or shall I totally change the geometry of the problem?
Thank you,
Bests
Beatrice



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Ing. Beatrice Pomaro
Universita' degli Studi di Padova
Dipartimento di Ingegneria Civile, Edile e Ambientale
Via F. Marzolo, 9 - 35131 Padova (Italy)
tel.: +39 049 8275592
e-mail: beatrice.pomaro_at_dicea.unipd.it<mailto:beatrice.pomaro_at_dicea.unipd.it>
Il 15-02-2018 16:18 Fasso, Alberto ha scritto:
Dear Beatrice,
you cannot calculate a linear attenuation coefficient unless in what in dosimetry
is called a "good geometry": both source and target being narrowly collimated.
In the "bad geometry" that you have (no collimation) you get in addition to linear
attenuation a buildup factor due to scattering inside the target.
Check on any good dosimetry textbook.
Alberto
________________________________________
From: owner-fluka-discuss_at_mi.infn.it<mailto:owner-fluka-discuss_at_mi.infn.it> <owner-fluka-discuss_at_mi.infn.it<mailto:owner-fluka-discuss_at_mi.infn.it>> on behalf of Beatrice Pomaro <beatrice.pomaro_at_dicea.unipd.it<mailto:beatrice.pomaro_at_dicea.unipd.it>>
Sent: Thursday, February 15, 2018 2:30 PM
To: Mauro Valente
Cc: Vasilis Vlachoudis; fluka-discuss; owner-fluka-discuss_at_mi.infn.it<mailto:owner-fluka-discuss_at_mi.infn.it>
Subject: Re: [fluka-discuss]: Attenuation coefficient for photons in a material
Thank you very much for your explanations,
so if I would like to estimate the linear attenuation coefficient through the different media, am I allowed to do the natural logarithmic ln(flux_in/flux_out) and divide it by the thickness, whatever the inner flux is?
Or would you suggest a more elegant approach?
Thank you once more,
Beatrice
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**************************************************
Ing. Beatrice Pomaro
Universita' degli Studi di Padova
Dipartimento di Ingegneria Civile, Edile e Ambientale
Via F. Marzolo, 9 - 35131 Padova (Italy)
tel.: +39 049 8275592
e-mail: beatrice.pomaro_at_dicea.unipd.it<mailto:beatrice.pomaro_at_dicea.unipd.it><mailto:beatrice.pomaro_at_dicea.unipd.it<mailto:beatrice.pomaro_at_dicea.unipd.it>>
Il 14-02-2018 15:53 Mauro Valente ha scritto:
I am not Fluka expert, but regarding the problem you pointed out, photon flux might not be the same in the different situations your are studying. Particularly, if you tally photon flux in the near of "entrance" surface, you may count both primary and scattered photons (it may depend on the FLUKA tally you used, "photon" or "beampart").
changing material shall vary scattering (backscattering, for the purposes of your problem, mainly) and therefore some differences could be present.
If "beampart" tally does not account (please check, I am not FLUKA expert) any kind of scattered particles (i.e. if you can be sure that inelastic/elastic scattered primary are not accounted by beampart tally), then you may compare this tally among your different setups. Otherwise, if "photons" in your tally include all types of photons, you should notice some differences at the entrance due to backscattering.
Best regards,
2018-02-14 10:21 GMT-03:00 Vasilis Vlachoudis <Vasilis.Vlachoudis_at_cern.ch<mailto:Vasilis.Vlachoudis_at_cern.ch><mailto:Vasilis.Vlachoudis_at_cern.ch<mailto:Vasilis.Vlachoudis_at_cern.ch>>>:
back scattering from the material maybe?
Cheers
Vasilis
________________________________
From: owner-fluka-discuss_at_mi.infn.it<mailto:owner-fluka-discuss_at_mi.infn.it><mailto:owner-fluka-discuss_at_mi.infn.it<mailto:owner-fluka-discuss_at_mi.infn.it>> [owner-fluka-discuss_at_mi.infn.it<mailto:owner-fluka-discuss_at_mi.infn.it><mailto:owner-fluka-discuss_at_mi.infn.it<mailto:owner-fluka-discuss_at_mi.infn.it>>] on behalf of Beatrice Pomaro [beatrice.pomaro_at_dicea.unipd.it<mailto:beatrice.pomaro_at_dicea.unipd.it><mailto:beatrice.pomaro_at_dicea.unipd.it<mailto:beatrice.pomaro_at_dicea.unipd.it>>]
Sent: Wednesday, February 14, 2018 11:36
To: fluka-discuss
Subject: [fluka-discuss]: Attenuation coefficient for photons in a material
Dear Fluka experts,
I am simulating an irradiation experiment with a Co60 source of samples made by a different material at the same distance (20cm) from the source. I have plotted the photon flux against the sample thickness, 10cm (here below) and I find curiously that the flux at the face in front of the source (_at_20cm) is never the same, in particular it is much different when the propagation is in air (no sample).
Can you, please, explain me how I can fix this aspect?
Thank you, bests
Beatrice
[X]
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Ing. Beatrice Pomaro
Universita' degli Studi di Padova
Dipartimento di Ingegneria Civile, Edile e Ambientale
Via F. Marzolo, 9 - 35131 Padova (Italy<https://maps.google.com/?q=Via+F.+Marzolo,+9+-+35131+Padova+(Italy&entry=gmail&source=g>)
tel.: +39 049 8275592
e-mail: beatrice.pomaro_at_dicea.unipd.it<mailto:beatrice.pomaro_at_dicea.unipd.it><mailto:beatrice.pomaro_at_dicea.unipd.it<mailto:beatrice.pomaro_at_dicea.unipd.it>>
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                                                         Medical Physics
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Received on Fri Feb 16 2018 - 18:31:26 CET

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