Re: FCAL test

[Matthew Shepherd <mashephe@indiana.edu>]

On Sep 15, 2007, at 11:07 AM, Elke-Caroline Aschenauer wrote:

> I have also the following questions. how critical is the size of the
> crystals, could we look in getting some radiation hard crystals from
> Hermes just for the center of the fcal.

Size is critical to get the tight packing fraction.  I think we  
almost need to tackle this from a physics standpoint.  If I remember  
right the radiation does drops of exponentially as one moves to  
larger radius.  (This is not dose, but rate and gives you some  
idead:  http://www.jlab.org/Hall-D/software/wiki/index.php/ 
FCAL_Backgrounds) This could mean only the blocks within 2 blocks of  
the beam hole get a hefty dose.  If this is the case, can we live  
with damaged blocks in that radius?  If we try to do something fancy  
just for those blocks then we create a boundary in the calorimeter  
there.  The problem is that then no shower in that region is  
contained in blocks of one type or other.  In addition alternate size  
blocks or some support that allows removal of central blocks would  
likely result in dead space between the blocks, which would be hard  
to deal with in reconstruction.  Certainly we need to do some  
thinking and simulation, but it is quite possible that lesser of all  
evils is just to leave with radiation damaged blocks near the beam.   
I think the one exception to this might be if one could get rad-hard  
blocks that are exactly the same size at the blocks we have, but then  
we would still have a boundary and "hybrid showers."  We just need to  
be careful that our rad-hard solution doesn't generate an effective  
hole in the calorimeter larger than we would have if we just let the  
inner blocks degrade.

-Matt