  The Cosmic-Ray Veto detector for the muon-to-electron conversion experiment
at Fermilab consists of four plastic scintillating counter layers read out by
silicon photo-multipliers through embedded wavelength-shifting fibers. In order
to increase the light yield in the most critical regions of the Cosmic-Ray Veto
detector for improved background rejection, a 1.8 mm diameter fiber is being
used in many of the detector's critical modules instead of the previously
planned 1.4 mm diameter fiber. This paper reports the testing procedure and
light properties of thirty-four 1.8 mm fiber spools, with measurements
performed using a custom-built scanner. We compare these new results with
previously published data from the 1.4 mm diameter fiber used for regions of
the cosmic-ray veto where the increased light yield is not required. In
addition, measurements of fiber aging were performed.
