# Re: Can anybody determine dose at the center of a sphere?

From: Alfredo Ferrari (alfredo.ferrari@cern.ch)
Date: Mon Feb 13 2006 - 17:20:38 CET

• Next message: Alberto Fasso': "Re: Can anybody determine dose at the center of a sphere?"

Arggghhhh!!!

Directing particles at the center is infinitely wrong!!! Indeed you should
get infinite as a result. To get an isotropic source requires an algorithm
emitting from a spherical surface (random point) in a direction which
points inside and which forms an angle with the local normal
distributed as cos(theta) dcos(theta). The routine sflood included in
fluka does just this for a 1 cm radius (multiply by the radius you wish
the position components).

The calling sequence is:

SUBROUTINE SFLOOD ( XXX, YYY, ZZZ, UXXX, VYYY, WZZZ )

where XXX,YYY,ZZZ is the returned position (on a 1 cm radius sphere, again
multiply all three for the radius you wish) and UXXX, VYYY, WZZZ is the
direction

The fluence you generate in this way will be uniform and isotropic
everywhere inside the sphere (of course if there is no material altering
it) and numerically equal to 1/ (pi R**2) where R is the radius you used.

Ciao
Alfredo

On Mon, 13 Feb 2006, Reddell, Brandon D wrote:

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> Dear FLUKA users,
>
> I have a very fundamental and rather simple question that nobody seems
> to be able to answer. How do you correctly determine dose at the center
> of a solid aluminum sphere. I want to compare FLUKA 3D results with
> results from others codes, such as Shieldose2 and GEANT4.
>
> I've included a test input file as an example. The results from SCORE
> and USRBIN 1) don't agree with each other, then 2) they aren't even
> close to that from the other codes. Ultimately, I would like to get the
> dose at the center of a sphere from an isotropic source/spectrum (hence
> my source command at the bottom). For now, I am directing all energy to
> the center -- the answer should be relatively close to that from an
> isotropic source.
>
> Can any body help me determine dose in Rad or Gy at the center of a
> solid sphere --- and provide an answer that consistent with what is
> published in literature?
>
> Sincerely,
>
> Brandon
>
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```--
+----------------------------------------------------------------------------+
|  Alfredo Ferrari                ||  Tel.: +41.22.767.6119                  |
|  CERN-AB                        ||  Fax.: +41.22.767.7555                  |
|  1211 Geneva 23                 ||  e-mail: Alfredo.Ferrari@cern.ch        |
|  Switzerland                    ||          Alfredo.Ferrari@mi.infn.it     |
+----------------------------------------------------------------------------+
```

• Next message: Alberto Fasso': "Re: Can anybody determine dose at the center of a sphere?"

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