Re: Particle biasing

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:

> --------------ms070301010804060504060505
> Content-Type: multipart/mixed;
> boundary="------------070204030100050006090707"
>
> This is a multi-part message in MIME format.
> --------------070204030100050006090707
> Content-Type: text/plain; charset=ISO-8859-2; format=flowed
> Content-Transfer-Encoding: quoted-printable
>
> 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.ch