Re: [fluka-discuss]: Co-60 source routine

From: Santana, Mario <msantana_at_slac.stanford.edu>
Date: Fri, 13 Dec 2013 10:22:57 -0800

Fabio,

This is not so much a FLUKA question anymore.
Anyway,… You want to get the dose for a given source activity. The activity is defined as [disintegrations/time], not [gammas/time]. For 60-Co, 99.88% of disintegrations result in the emission of TWO gamma (1.17 MeV and 1.33 MeV, respectively), but your simulations are initially normalized to histories, which are either one gamma or the other. So there you get your answer (=two).

Also note that you are neglecting the emitted betas (I agree most will be self-absorbed in your source) and the other disintegration path (0.12%) that would only lead to one 1.33 MeV gamma.

Mario

From: Fabio Pozzi <fabio.pozzi_at_cern.ch<mailto:fabio.pozzi_at_cern.ch>>
Date: Friday, December 13, 2013 2:28 AM
To: Mario Santana <msantana_at_slac.stanford.edu<mailto:msantana_at_slac.stanford.edu>>, fluka-discuss <fluka-discuss_at_fluka.org<mailto:fluka-discuss_at_fluka.org>>
Subject: RE: [fluka-discuss]: Co-60 source routine

Hello Mario,
I found out that the main problem is the normalization. Actually I did not take into account that I have not to use the total source activity for the normalization, but only the fraction that is emitted within the actual solid angle, i.e {15 GBq*omega/4pi} (where omega is the solid angle covered by my cone): this is the actual activity for the normalization.
Moreover I have a further question: because of my energy sampling (once a photon of 1.17 MeV and once a photon of 1.33 MeV), should I also multiply by 2 in the end of the normalization? If I am not wrong this should take into account the photon yield of the Co-60 source (i.e. for each disintegration two photons are emitted).

Thank you for your help.

Cheers,

Fabio

From: Santana, Mario [mailto:msantana_at_slac.stanford.edu]
Sent: 12 December 2013 20:23
To: Fabio Pozzi; fluka-discuss_at_fluka.org<mailto:fluka-discuss_at_fluka.org>
Subject: Re: [fluka-discuss]: Co-60 source routine

Fabio,

I checked that you had the right energies in your subroutine (typically an error of units, e.g. GeV instead of MeV could explain some discrepancies) and it seems OK. I am going to assume for now that the angular spectrum is fine although the implementation seems quite cumbersome (by the way, for best practice try to avoid mixing integers with real numbers, specially in ratios). Do dose rate maps look consistent with the emission angle?
I guess the crucial point is the normalization. Which factor did you use to convert pSv/primary into mSv/h/15GBq?

Mario


From: Fabio Pozzi <fabio.pozzi_at_cern.ch<mailto:fabio.pozzi_at_cern.ch>>
Date: Thursday, December 12, 2013 9:35 AM
To: fluka-discuss <fluka-discuss_at_fluka.org<mailto:fluka-discuss_at_fluka.org>>
Subject: [fluka-discuss]: Co-60 source routine

Dear all,

I am simulating a Co-60 source emitting photons within a certain irradiation angle (30 degrees). I wrote a dedicated source routine which sample the emission direction and position according to my needs. This "seems" to work properly. In order to reproduce the two Co-60 photons I make my routine sample the photon energy with equal probability (0.5 each), i.e. once it chooses 1.17 MeV and once 1.33 MeV. I am scoring the dose-rate with USRBIN.
The point is that when I normalize the FLUKA dose rate (which is in pSv/pr) to the source activity (15 GBq in my case) I obtain a dose rate at 1 m from the source around the Sv/h, instead it should be in the mSv/h range (cross-check with Nucleonica).
If you have any idea/hints please let me know (I attached my input file and the source routine).

Thank you in advance.

Cheers,

Fabio
Received on Fri Dec 13 2013 - 20:13:40 CET