[fluka-discuss]: Re: [fluka-discuss]: Scoring ambient dose​ rate; deviation fro​m MCNP-results

From: Alberto Fasso <fasso_at_mail.cern.ch>
Date: Thu, 2 Jul 2015 15:13:23 +0200

Dear Alexander,

two comments about your problem.

1) it is the first time I hear about TÜV*, so I don't know anything about
their techniques and procedures. But didn't it occur to you that "The
results of MCNP and the TÜV-results are identical" because TÜV did also
use MCNP as you did?

2) anyway, it is a serious issue, because a disagreement of this size has
never been found with MCNP, and especially in a purely electromagnetic
problem. To clarify the situation, therefore, it would be easier if the
comparison was made in the simplest possible way. I suggest that you
try it again by not scoring ambient dose equivalent, but simply fluence,
differential in energy. I would also do the calculation with only Co-60,
without the complication of Cs-137.


On Thu, 2 Jul 2015, "Alexander Götzelmann (alexander.goetzelmann_at_hs-furtwangen.de)" wrote:

> Thank you a lot for your help. Sorry for my late reply, yesterday I was out
> of office.
> The results should be deemed correct, because the TÜV* simulated the same
> model with the same input-data. The results of MCNP and the TÜV-results are
> identical.
> I find some mistake in my input: I accidently used a wrong material-mixture
> for the the filling of the barrel (the Region "BORSAE" in the Input I sent
> you in the previous mail is now changed to Region "SCHROTTC" with a new
> material-mixture). Now the ambient dose rate is a bit lower because of the
> higher self-shielding. But the FLUKA results are still higher by a factor of
> approximately 3 to 4.
> In MCNP I used the ICRP116 dose conversion coefficients for photons. FLUKA
> uses the ICRP74. The dose conversion coefficient of ICRP74 for the energy of
> Co-60 is higher by a factor of 1,3. So the difference of this two data bases
> can't explain the huge deviation.
> If you look in the MCNP-Input-File you will see that I used a source, which
> consists of the two radioisotopes Co-60 and Cs-137 with the ratio 75:25. In
> FLUKA I make two runs (one with Co-60 and the other one with Cs-137) and
> calculate the total ambient dose rate by hand. Because of the lower energy ,
> Cs-137 doesn't contribute to the ambient dose rate outside the barrel (My
> runs approve this). So a run in FLUKA with just Co-60 should be match with
> the MCNP-result.
> The source (mixture of Co-60 and Cs-137) has an activiy of 1E11 Bq.
> In the attachment you find the MCNP-Input-File and my new FLUKA-Input-File.
> And yes, I used the f4-tally in MCNP.
> thank you,
> Alexander
> * "TÜV SÜD is a leading technical service corporation catering to the
> INDUSTRY, MOBILITY and CERTIFICATION Segments . Its range of services
> embraces consultancy, inspection, tests and expert reports as well as
> certification and training" [TÜV SÜD].

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Received on Thu Jul 02 2015 - 16:35:10 CEST

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