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

From: Andrea Fontana <andrea.fontana_at_pv.infn.it>
Date: Wed, 28 Feb 2018 19:12:35 +0100 (CET)

Hi Beatrice,
    the reply to your first question is yes, because the attenuation
coefficient assumes that every particle of the beam that interacts
is removed from the beam: if you record the current with USRBDX
but you have scattering in your geometry, this is not anymore
true because, for example, you can have particles deflected by
a first interaction that are able to hit the detector after a second
interaction and the situation is more complex.

If you use USRBIN with a fine mesh (second question), you can have
a better idea of where the particles interact (depending on what
you are scoring), but the definition of the attenuation coefficient
is still valid only for collimated beams. You can always calculate
a buildup factor for your problem.

Andrea

>
>
> Thank you very much, very helpful.
> just to be sure: in the example of ''good geometry'' that you sent me,
> if the source would be isotropic and the foil was smaller and thicker,
> let's say a cube 10cm side (i.e. removing the hypotheses of good
> geometry) then the USRBDX applied on the front and back face would not
> be representative of the number of particles crossing them, correct? And
> a USRBIN/BEAMPART card would be more appropriate to appreciate the decay
> in the flux at the two opposite faces, in this case, am I wrong?
> Although we will have a bad estimate of the attenuation coefficient in
> the case of poor geometry unless we consider a buildup factor.
> Thank you once more,
> Bests
> Beatrice
>
> ---
>
> **************************************************
> 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
>
> Il 22-02-2018 19:17 Andrea Fontana ha scritto:
>
>> Dear Beatrice,
>> I have run your input file and I send you a modified version which
>> should give you a good result (I hope).
>>
>> In the original version, your input does not run because of the EMFCUT
>> card: you have set a production cut at 10 MeV and, since this is
>> greater than 100 keV, you should also set WHAT(3)=1 in the same card
>> (see manual about FUDGEM).
>>
>> With this change, Fluka runs: in the 2 USRBDX cards (in and out of the
>> absorber) I have integrated over the energy by indicating only 1 energy
>> bin. In this way in the output you have a single number that you can
>> useas I_0 and I in the coefficient formula.
>> I have notice another small detail: since you are scoring BEAMPART,
>> which is directed by definition downstream along the beam axis, you do
>> not need a two-way scorer and you can use for example a one-way
>> current, as I have done. The results should not change anyway
>> (there is no backward current).
>>
>> This should work. Give it a try and let me know...
>>
>> To get acquainted with these studies, perhaps is good to have a small
>> example to calculate the linear attenuation coefficient in a simpler
>> setup with a single material and to compare it with tabulated values.
>> I send you an example (mu.inp) where you can calculate with the same
>> technique the linear attenuation coefficient for photons of 1 MeV
>> energy in an aluminum slab (thickness 1 mm). Using this method and
>> your formula, I get
>>
>> mu/rho=0.06169
>>
>> to be compared with the NIST tables
>> (https://physics.nist.gov/PhysRefData/XrayMassCoef/ElemTab/z13.html [1])
>>
>> mu/rho=0.06146
>>
>> Hope this helps and kind regards,
>> Andrea
>>
>> Dear Andrea,
>> thank you everyone; I've followed your suggestions however I find it
>> difficult to use USRBDX results to compute the linear attenuation
>> coefficient. I should do the ratio of which quantities from the output
>> files, exactly?
>> I've included in the attached input file the two detectors for scoring
>> the flux at the section between rAir1 and rSample1 and viceversa.
>> Thank you,
>> Bests
>> Beatrice
>>
>> ---
>>
>> **************************************************
>> 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
>>
>> Il 20-02-2018 19:38 Andrea Fontana ha scritto:
>>
>> Dear Beatrice,
>> there is an easier way to calculate the attenuation coefficient
>> by using the USRBDX card on BEAMPART, by scoring the particles
>> current thrpough a surface. You can find an example in this message
>> (and related thread):
>>
>> http://www.fluka.org/web_archive/earchive/new-fluka-discuss/9105.html
>> [2]
>> [1]
>>
>> Regarding the second question, you need a collimated beam to use
>> your formula. In case of broadened beam this formula underestimates
>> the required thickness because photons can be scattered and you
>> have no control on the path lengths in the absorber. There is
>> a modified formula where you can include a correction factor.
>> You can find a discussion at this link:
>>
>> https://www.nucleonica.com/Application/Help/Helpfiles/AttenuationGammaRadiation.htm
>> [3]
>> [2]
>>
>> Hope this helps.
>> Kind regards,
>> Andrea
>>
>> 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
>>
>> ---
>>
>> **************************************************
>> 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
>>
>> On Fri, Feb 16, 2018 at 5:49 PM, Beatrice Pomaro
>> <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
>>
>> ---
>>
>> **************************************************
>> Ing. Beatrice Pomaro
>>
>> Universita' degli Studi di Padova
>> Dipartimento di Ingegneria Civile, Edile e Ambientale
>> Via F. Marzolo, 9 - 35131 Padova (Italy [1])
>> tel.: +39 049 8275592 [2]
>> e-mail: 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>
>> 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. Fassƒ’‚². 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
>>
>> ---
>> **************************************************
>> Ing. Beatrice Pomaro
>>
>> Universita' degli Studi di Padova
>> Dipartimento di Ingegneria Civile, Edile e Ambientale
>> Via F. Marzolo, 9 - 35131 Padova (Italy [1])
>> tel.: +39 049 8275592 [2]
>> 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
>>
>> ---
>> **************************************************
>> Ing. Beatrice Pomaro
>>
>> Universita' degli Studi di Padova
>> Dipartimento di Ingegneria Civile, Edile e Ambientale
>> Via F. Marzolo, 9 - 35131 Padova (Italy [1])
>> tel.: +39 049 8275592 [2]
>> 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]
>>
>> --
>> **************************************************
>> Ing. Beatrice Pomaro
>>
>> Universita' degli Studi di Padova
>> Dipartimento di Ingegneria Civile, Edile e Ambientale
>> Via F. Marzolo, 9 - 35131 Padova (Italy
>> [1]<https://maps.google.com/?q=Via+F.+Marzolo,+9+-+35131+Padova+(Italy&entry=gmail&source=g
>> [4]
>> [3]
>> [1]>)
>> tel.: +39 049 8275592 [2]
>> 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>>
>>
>> --
>>
>> ******************************************************************************************************************
>> ******************************************************************************************************************
>>
>> Prof. Mauro Valente, PhD.
>>
>> Medical Physics
>>
>> IFEG - CONICET &
>> University of Cordoba
>> Argentina
>>
>> Office 102 - Laboratory 448
>> TE: +54 351 4334050 ext. 102 [3]
>> FAX: +54 351 4334054 [4 [5]]
>>
>> http://www.famaf.unc.edu.ar/~valente/ [5] [4 [5]] [5 [4]]
>>
>> ******************************************************************************************************************
>> ******************************************************************************************************************
>>
>> __________________________________________________________________________
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>> Links:
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>> [8]
>> [7]
>> [2] tel:+39%20049%20827%205592
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>> [6] https://www.fluka.org/fluka.php?id&not;c_info [9] [6 [10]]
>>
>> Links:
>> ------
>> [1]
>> http://www.fluka.org/web_archive/earchive/new-fluka-discuss/9105.html
>> [2]
>> [2]
>> https://www.nucleonica.com/Application/Help/Helpfiles/AttenuationGammaRadiation.htm
>> [3]
>> [3]
>> https://maps.google.com/?q=Via+F.+Marzolo,+9+-+35131+Padova+(Italy&amp;entry=gmail&amp;source=g
>> [8]
>> [4] http://www.famaf.unc.edu.ar/~valente/ [5]
>> [5] https://www.fluka.org/fluka.php?id&Acirc;&not;c_info [7]
>> [6] https://www.fluka.org/fluka.php?id&amp;not;c_info [10]
>> [7]
>> https://maps.google.com/?q=Via+F.+Marzolo,+9+-+35131+Padova+(Italy&amp;amp;entry=gmail&amp;amp;source=g
>> [11]
>
>
> Links:
> ------
> [1] https://physics.nist.gov/PhysRefData/XrayMassCoef/ElemTab/z13.html
> [2]
> http://www.fluka.org/web_archive/earchive/new-fluka-discuss/9105.html
> [3]
> https://www.nucleonica.com/Application/Help/Helpfiles/AttenuationGammaRadiation.htm
> [4]
> https://maps.google.com/?q=Via+F.+Marzolo,+9+-+35131+Padova+(Italy&amp;entry=gmail&amp;source=g
> [5] http://www.famaf.unc.edu.ar/~valente/
> [6] https://www.fluka.org/fluka.php?id&Atilde;&sbquo;&Acirc;&not;c_info
> [7] https://www.fluka.org/fluka.php?id&amp;Acirc;&amp;not;c_info
> [8]
> https://maps.google.com/?q=Via+F.+Marzolo,+9+-+35131+Padova+(Italy&amp;amp;entry=gmail&amp;amp;source=g
> [9] https://www.fluka.org/fluka.php?id&amp;not;c_info
> [10] https://www.fluka.org/fluka.php?id&amp;amp;not;c_info
> [11]
> https://maps.google.com/?q=Via+F.+Marzolo,+9+-+35131+Padova+(Italy&amp;amp;amp;entry=gmail&amp;amp;amp;source=g


-- 
========================================================================
Dr. Andrea Fontana                    tel: +39 0382 987991
Istituto Nazionale                    fax: +39 0382 423241
di Fisica Nucleare
Sezione di Pavia                      e-mail: andrea.fontana_at_pv.infn.it
Via Bassi 6                           web   : www.pv.infn.it/~fontana
27100 PAVIA, Italy
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Received on Wed Feb 28 2018 - 20:50:31 CET

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