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

From: Joachim Vollaire <joachim.vollaire_at_cern.ch>
Date: Tue, 20 Feb 2018 17:41:58 +0000

Dear Beatrice

As suggested by Alberto, you should use BEAMPART instead of PHOTON to get only the contribution of the particles emitted by the Co-60 decay (otherwise you will get all photons -> annihilation after pair production, photons after Compton scattering which accounts for the buildup factor if you look text book…).

Using BEAMPART/USRBIN, you can eventually extract the decrease of the BEAMPART population while moving through the shielding material. If you are close enough to the “ideal” geometry of a collimated beam through a “thin” shielding you can fit this curve by an exponential decrease to get the linear attenuation coefficient (and derive other quantities as half-value layer/TVL…).

Greetings
Joachim


From: owner-fluka-discuss_at_mi.infn.it [mailto:owner-fluka-discuss_at_mi.infn.it] On Behalf Of Beatrice Pomaro
Sent: 20 February 2018 16:18
To: Mauro Valente <mauro.valente_at_gmail.com>; Vasilis Vlachoudis <Vasilis.Vlachoudis_at_cern.ch>; fluka-discuss <fluka-discuss_at_fluka.org>; Owner fluka discuss <owner-fluka-discuss_at_mi.infn.it>
Subject: Fwd: Re: [fluka-discuss]: Attenuation coefficient for photons in a material


Dear Fluka experts,
can someone check whether the attached input file is correct for the computation of the linear attenuation coefficient of a sample at 20cm from a gamma-source in a collimated geometry, please?
BIN 42 and 43 correspond to two thin bins (2cm long in direction of the beam) in the front and back face of the sample, which is 10cm thick.
I would like to know in particular if SCORE and AUXSCORE cards are correctly defined in the input file.
Therefore I would compute the attenuation coefficient as: ln(BIN 43/BIN 42), divided by the thickness. Is it correct?
Would you use the same procedure also for a non-collimated geometry? Or would you say that it is meaningless to reproduce a non-collimated experiment for the computation of the attenuation coefficient?
Thank you for your attention,
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>


On Fri, Feb 16, 2018 at 5:49 PM, Beatrice Pomaro <beatrice.pomaro_at_dicea.unipd.it<mailto:beatrice.pomaro_at_dicea.unipd.it>> wrote:

Dear Dr. Fasso',
thank you, I read that the score card gives a result by region of the density of stars produced by the selected particles (photons in my case). Does it mean that to compute the linear attenuation coefficient of the medium I have to calculate this quantity with and without the absorbing medium and do the natural logarithm of the ratio: ln(beampart_with sample/beampart_without sample) and divide it by the thickness of the sample?
Thank you for your explanation,
Best regards,
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<https://maps.google.com/?q=Via+F.+Marzolo,+9+-+35131+Padova+(Italy&entry=gmail&source=g>)
tel.: +39 049 8275592<tel:+39%20049%20827%205592>
e-mail: beatrice.pomaro_at_dicea.unipd.it<mailto:beatrice.pomaro_at_dicea.unipd.it>



Il 16-02-2018 17:03 Fasso, Alberto ha scritto:
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
________________________________________
From: Beatrice Pomaro <beatrice.pomaro_at_dicea.unipd.it<mailto: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<mailto:owner-fluka-discuss_at_mi.infn.it>
Subject: Re: [fluka-discuss]: Attenuation coefficient for photons in a material

Ok, thank you very much Dr. Fassò. 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<https://maps.google.com/?q=Via+F.+Marzolo,+9+-+35131+Padova+(Italy&entry=gmail&source=g>)
tel.: +39 049 8275592<tel:+39%20049%20827%205592>
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 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><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: 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><mailto: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




---
**************************************************
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<tel:+39%20049%20827%205592>
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>><mailto: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>><mailto: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


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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>><mailto: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>><mailto: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>><mailto: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]

--
**************************************************
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><https://maps.google.com/?q=Via+F.+Marzolo,+9+-+35131+Padova+(Italy&entry=gmail&source=g>)
tel.: +39 049 8275592<tel:+39%20049%20827%205592>
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>><mailto: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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Received on Tue Feb 20 2018 - 20:08:24 CET

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