question on pair spectrometer shielding

[Richard Jones <richard.t.jones@uconn.edu>]

Alex,

I am going through the new geometry for the photon beamline, and have a 
question.  What is the purpose of the large iron wall 17.8cm thick at 
the downstream end of the pair spectrometer?  It seems that this will 
play no role, since there is already much more iron that this in the 
yoke and poles of the dipole itself.  Is this a crude description of the 
support structure for the magnet?  If it is not needed to shield the 
counters then can I get rid of it?  If you think we need to shield the 
counters, can we somehow reduce its dimensions? 

-Richard Jones