From: Stefan Roesler <sroesler_at_mail.cern.ch>

Date: Fri, 17 Oct 2008 09:11:50 +0200

Date: Fri, 17 Oct 2008 09:11:50 +0200

Hi Alfredo,

I looked into the problem of David and found some strange things:

If I set Biasing/What(3)='blank' and Sdum='USER', e.g.

BIASING 0.0 BlckHole @LASTREG USER

I get a stop

Abort called from DOEIMB reason .NOT.LIMPRE Run stopped!

STOP .NOT.LIMPRE

I have the impression that the code thinks there is no importance biasing

and is missing some initialization(?)

Furthermore, if I set What(3)=1 and use David's usimbs I get consistent

results with the other two cases while if I set What(3)=2 I can confirm

Davids observations. Taking into accound that usimbs sets FIMP either 1 or

2 it looks stange to me that this should be due to biasing-artifacts. What

do you think?

btw, to David: the default thresholds for transport and production of

gamma and e+/e- might not be suitable (too high) as you have primaries

down to 10keV(?)

Cheers

Stefan

On Tue, 14 Oct 2008, David Horvath wrote:

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*> boundary="------------070204030100050006090707"
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*>
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*> This is a multi-part message in MIME format.
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*> Content-Type: text/plain; charset=ISO-8859-2; format=flowed
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*>
*

*> Dear Alfredo
*

*>
*

*> I reran the three cases with 10 runs and 1,000,000 primaries in each
*

*> run. The case with no biasing, and the sliced geometry biasing gave
*

*> approximately the same result, but with usimbs.f the result is still off.
*

*>
*

*>
*

*> I don't know what can be wrong with my usimbs.f, as fas as I know it
*

*> only making the paricles split or russian roulette, and can't effect the
*

*> value of the partice flux.
*

*>
*

*> Can somebody check my files to help my figure out what can be wrong with
*

*> my usimbs.f?
*

*>
*

*> Thank you for you help.
*

*>
*

*> Best regards,
*

*>
*

*> David HORVATH
*

*> engineering physicist student
*

*> Budapest University of Technology and Economics
*

*>
*

*> PS.:
*

*> I attached the user files zipped.
*

*>
*

*>
*

*> Alfredo Ferrari =EDrta:
*

*> > Dear David
*

*> >=20
*

*> > different biasing options/ways must result in the same numbers once the=
*

*>
*

*> > results converged properly, so you are right in inquiring why you didn'=
*

*> t=20
*

*> > get compatible numbers. I see two possible problems with your numbers:
*

*> >=20
*

*> > a) you made only two runs -> the statistical error estimation is surely=
*

*>
*

*> > very poor. That is, the errors reported could well be far from real=
*

*> ity.
*

*> > A minimum of 5 runs (much better at least 10) are required for a
*

*> > meaningful evaluation of the statistical error. For example, instea=
*

*> d of
*

*> > doing 2 runs of 1,000,000 each, you could have done 10 runs of 200,=
*

*> 000
*

*> > In that case you would have used the same CPU time, the results wou=
*

*> ld
*

*> > have been exactly the same (for the same initial random numbers) as=
*

*>
*

*> > for the 2, 1,000,000 each, runs, but statistical errors could have =
*

*> been
*

*> > different and surely better estimated. This could explain the
*

*> > difference between
*

*> > no biasing:
*

*> > Tot. response (p/cmq/pr) 4.3660339E-08 +/- 2.982906 %
*

*> >=20
*

*> > sliced geometry with importance biasing:
*

*> > Tot. response (p/cmq/pr) 3.8885091E-08 +/- 9.0743139E-02 %
*

*> > which is roughly 11% against a combined error of 3%. They could
*

*> > still be compatible, particularly if the errors are not properly
*

*> > estimated
*

*> >=20
*

*> > b) the results with usimbs.f is indeed far out (> 10 times). Obviously
*

*> > it should not be, are you sure you used usibms properly?
*

*> >=20
*

*> > Ciao
*

*> > Alfredo
*

*> >=20
*

*> > On Sat, 11 Oct 2008, David Horvath wrote:
*

*> >=20
*

*> >> Dear Fluka users,
*

*> >>
*

*> >> I try to calculate a shielding for a spent fuel of a teaching reactor,=
*

*>
*

*> >> and I tried out different ways of importance biasing, but they gave
*

*> >> different results which i can't explain.
*

*> >>
*

*> >> The results
*

*> >>
*

*> >> usrtrack_21, inside the shielding:
*

*> >>
*

*> >> no biasing:
*

*> >> Tot. response (p/cmq/pr) 9.8644884E-04 +/- 0.4479266 %
*

*> >>
*

*> >> sliced geometry with importance biasing:
*

*> >> Tot. response (p/cmq/pr) 9.8818401E-04 +/- 0.1642988 %
*

*> >>
*

*> >> with usimbs.f:
*

*> >> Tot. response (p/cmq/pr) 9.8289608E-04 +/- 9.9353164E-02 %
*

*> >>
*

*> >> These results are quite the same.
*

*> >>
*

*> >> usrtrack_22, last layer of shelding:
*

*> >>
*

*> >> no biasing:
*

*> >> Tot. response (p/cmq/pr) 4.3660339E-08 +/- 2.982906 %
*

*> >>
*

*> >> sliced geometry with importance biasing:
*

*> >> Tot. response (p/cmq/pr) 3.8885091E-08 +/- 9.0743139E-02 %
*

*> >>
*

*> >> with usimbs.f:
*

*> >> Tot. response (p/cmq/pr) 5.2892267E-07 +/- 0.2122020 %
*

*> >>
*

*> >> These should be also the same.
*

*> >>
*

*> >> For each simulation I used 2 runs with 1,000,000 primaries in each run=
*

*> =2E
*

*> >>
*

*> >> To validate the results, I used MCNP4C with sliced geometry with the
*

*> >> same importance biasing used in Fluka.
*

*> >>
*

*> >> The mcnp results (5,000,000 primaries)
*

*> >>
*

*> >> Inside the shielding:
*

*> >> cell (30<40[0 0 0]) 1.21985E-03 0.0024
*

*> >> Last layer of shelding:
*

*> >> cell 109 4.55585E-08 0.0056
*

*> >>
*

*> >>
*

*> >> Is it a normal behavior of the biasing, or I did something wrong?
*

*> >>
*

*> >>
*

*> >> Thank you for your answer.
*

*> >>
*

*> >> Best regards,
*

*> >>
*

*> >> David HORVATH
*

*> >> engineering physicist student
*

*> >> Budapest University of Technology and Economics
*

*> >>
*

*> >>
*

*> >> PS.:
*

*> >> I attached the input, usrtrack, source.f, usimbs.f files, and the mcnp=
*

*>
*

*> >> input and output zipped.
*

*> >>
*

*> >=20
*

*>
*

-- ___________________________________ Stefan Roesler CERN, SC/RP CH-1211 Geneva 23 Switzerland Phone: +41-22-7679891 Fax: +41-22-7669639 E-mail: Stefan.Roesler_at_cern.chReceived on Sat Oct 18 2008 - 08:51:54 CEST

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