next up previous
Next: TDC Information Up: Measurements and Results Previous: Measurements and Results


ADC Information

The extracted attenuation length values are plotted in Fig. 9, for all fiber bundles.

Figure 9: Attenuation length measurements for various fibers. The Pol.Hi.Tech. single-clad fibers appear to have been broken or stressed at the locations where the discontinuities appear in their curve (unconnected squares).


\includegraphics [height=94.5mm,angle=0,clip=]{adc_fits.eps}

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 $\lambda = (285 \pm 7)$ cm, whereas the more stable 5/4 stack produced $\lambda = (283 \pm 2)$ cm, in excellent agreement. The Kuraray Y2001 batch in a 5/4 stack configuration yielded a consistent $\lambda = (273 \pm 3)$ 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 $\approx$125 cm and $\approx$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 $\lambda = (234 \pm 3)$ 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 $\vec{B}_{vertical}$ and $\vec{B}_{axial}$ (parallel to the fibers) were recorded, using a NMR probe. The field components were measured in $\approx$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.


next up previous
Next: TDC Information Up: Measurements and Results Previous: Measurements and Results
Web Master
2001-10-29