Each Roman pot contains a position detector, which is used
to determine the (x,y) coordinate of the deflected proton
at the pot position. These detectors should be very reliable
as they will be
located in the tunnel and consequently difficult
to access. The resolution requirements are modest, since uncertainties
in the beam position and location of the pot make a
point resolution of better than 100 
m
superfluous. The radiation environment at an 
distance from the
beam is only about
0.03 Mrad per year of normal running,
so the radiation hardness of the
detector is not an overriding concern.
The final detector choice should be
comparable in
cost to the Roman pots and should
be easily integrated into the standard DØ data block and trigger.