[Gate-users] A Forbid revelation

[Andrej Studen]

Dear Gaters!

I was trying to use Forbid as advertised by

http://wiki.opengatecollaboration.org/index.php/Users_Guide_V7.1:Source

I found that there is one vital piece of information missing. Namely - 
there shouldn't be any pieces of geometry created after Forbid command 
is issued. This is because the Gate's point source generator stores only 
the pointer to the physical volume of the cold area. If a piece of 
geometry is added afterwards, the whole tree gets rebuild and pointers 
can point to different entities, resulting in cold area not being cold 
at all.

Also, the check whether the emission point is in the cold area comes 
only after the point is shifted due to positron range. The difference is 
somewhat philosophical but still important - the filter looks at 
annihilation point rather than emission point. Maybe this is worth 
rethinking.

Cheers

Andrej