[gate-users] Compound Phantom

[Giovanni Santin]

Dear Ray

yes, if the sources are defined as simple GPS sources without the
'confine' command, they will overlap. This happens because in this case
GPS does not do any check on the Geant4 geometry, it's a purely
mathematical generation of points in the defined shape.
It's quite easy though in this case to subtract 1/8th of the activity
from the definition of the spherical sources to have the correct
activity ratio. I would definitely suggest this method.

If you define your 'real Geant4 geometry' volumes (the ellipsoid, and the 
spheres as daughters) and then in the definition of the sources you use 
'confine' to confine them inside the 'real volumes', then sphere and 
ellipsoid are not overlapping (in the geometry check the points in the 
sphere are not also in the ellipsoid).

Using 'confine' is sometimes useful for complex source geometry
(for example in your case if the source radioisotope is different in
ellipsoid and spheres, then you definitely don't want to have the
overlap).

However sources using 'confine' are normally computationally slower.

Hope this helps,
Best regards,
--
Giovanni
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Giovanni Santin
Space Environments and Effects Analysis
ESA - ESTEC - TEC-EES
Keplerlaan 1, 2200 AG Noordwijk, Netherlands
e-mail: giovanni.santin at esa.int
Tel: +31 71 565 6267
Fax: +31 71 565 4999



On Thu, 12 Aug 2004, Ray Raylman wrote:

> I would like to create a phantom consisting of four hot spheres of
> different diameter imbedded inside a warm ellipsoid (sphere to ellipsoid
> radioactivity
> ratio of 8:1).  If I just overlap the sources (encase the spheres within
> the ellipsoid), won't some of the activity assigned to the ellipsoid be
> present within the spheres?  Is there any way to exclude the ellipsoid
> activity from the spheres?  
> 
> 
> Thanks, Ray Raylman
> 
> 
> Raymond R. Raylman, Ph.D.
> Associate Professor/Vice Chair for Research
> Dept of Radiology/Box 9236
> West Virginia University
> Morgantown, WV, 26506
> Phone: 304-293-1973
> _______________________________________________
> gate-users mailing list
> gate-users at lphe1pet1.epfl.ch
> http://lphe1pet1.epfl.ch/mailman/listinfo/gate-users
>