The extracted attenuation length values are plotted in Fig. 9, for all fiber bundles.
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It is evident that the attenuation lengths of the Kuraray fibers are
quite reproducible between different fiber samples, as well as
different geometrical configurations. The loose bundle (black tubing)
configuration resulted in
cm, whereas the more
stable 5/4 stack produced
cm, in excellent
agreement. The Kuraray Y2001 batch in a 5/4 stack configuration
yielded a consistent
cm.
From the single-clad Pol.Hi.Tech. bundle results, it was concluded
that there existed at least two points along the fiber bundle where
the fibers may have been broken, thus resulting in the discontinuities
seen in the attenuation data at distances of 125 cm and
180 cm from the Fiber Left PMT. Thus, the extraction of the
attenuation length for this bundle was meaningless.
The Pol.Hi.Tech. multi-clad fibers had an attenuation length of
cm, considerably shorter that the Kuraray
fibers.
The Group-3 and 5 measurements demonstrated that the attenuation length did not depend on the precise positioning of the fibers at beam height nor on the effective thickness of scintillating fiber material, as expected. The Left/Right ADC ratio of the fiber PMT's remained constant during these measurements.
Finally, past experience with running in the M11 area has shown that
the stray magnetic field of the TRIUMF Cyclotron can affect PMT gains.
Therefore, measurements of
and
(parallel to the fibers) were recorded, using a NMR probe. The field
components were measured in
20 cm intervals along the entire
range of locations of the PMT's, for the full length scans of the
measurements. The PMT's are most susceptible to the axial field. Its
value was below 0.5 G nearly everywhere, except around 1.5 m from the
beam center toward the right fiber PMT, where it became around 2 G.
In order to dispell concerns of the effect of the magnetic field,
several of the measurements were repeated (Group-4) by reversing the
direction of the fiber bundle, and thus the PMT's, from left to right.
The reversed measurements yielded the same value for the attenuation
length as that from the forward scans, within error bars.