The silicon-tungsten calorimeters [30] are situated either
side of OPAL, 2.389 m in the 
direction from the interaction point. They
were installed in 1993 to give an improvement on the luminosity measurement.
They are sampling calorimeters and consist of 19
layers of sampling silicon separated by 18 layers of tungsten. Each calorimeter
is divided azimuthally into 16 wedges and can achieve a spatial resolution in
of 
10 
m and an energy resolution in units of GeV of:
 |
(2.5) |