Dear Experts,

This is a similar problem as Jyoti’s . Zero result after biasing - #13 by horvathd

Please find attached the input file. My results are for VOID=AIR as well as VOID=VACUUM. ( 1 cycle Run to check the input).
My geometry is cylindrically symmetrical. Bias layer thickness = 1.2 cm Lead. 25 Co-60 sources, hence source.f is used.3010b.inp (10.0 KB) source.f (12.7 KB) VoidAir,55.7to75.7.lis (812 Bytes) VoidVacuum,55.7to75.7.lis (812 Bytes)

1. Void = Air: The Dose rate starts falling from R=55.7 to R=59.7 (as expected), through shield; it falls to zero then…later again the values are scored but larger than that at inner shields. Is anything wrong with the Biasing given?
2. Void = Vacuum: it falls initially, logical, zero in between, again a value…but no score outside the shield (R=73.7 to R=75.7) - implies something is not okay with the Biasing applied…
Can you please help me with some errors which you can find with my approach and help me find the solution ?
Thanks and regards,
Raksha.

Dear Raksha,

the issue is with your source routine. You left the default particle direction assignment as is:

``````TXFLK  (NPFLKA) = UBEAM
TYFLK  (NPFLKA) = VBEAM
TZFLK  (NPFLKA) = WBEAM
``````

This means the direction cosines `UBEAM`, `VBEAM` and `WBEAM` are taken from the BEAMPOS card (if it is not present, then the direction is along the positive z axis).

In the source routine the Isotropic angular divergence option set on the BEAM card is not taken into account. You need to specify it manually.

The easiest way is to replace the default 3 lines with the following one:

``````CALL RACO(TXFLK(NPFLKA),TYFLK(NPFLKA),TZFLK(NPFLKA))
``````

With the `RACO` subroutine FLUKA will automatically sample a random direction from an isotropic distribution.

Cheers,
David

Good morning David,

Thank you very much. It worked.

Regards,
Raksha.