A scintillating fiber tester is currently under construction. The
schematic of this device is shown in Fig. 
. A quartz
fiber carries modulated light from a UV lamp to the fiber to be tested.
The UV lamp has its peak output at 365nm which is close to the peak of the
primary scintillation in the fiber ( 
350nm). The UV excites the fluors
in the plastic scintillating fiber which give off visible light. A photomultiplier
tube at the end of the plastic fiber views the light output. The signal from
the photomultiplier and a reference signal from the chopper go to a lock-in
amplifier. The output of the lock-in is then proportional to the light output
from the scintillating fiber. Another photodetector not shown views the UV
lamp directly to provide the normalization. The quartz fiber may be positioned
anywhere along the scintillating fiber under computer control and also (not
shown in the figure) stepped from one fiber to another across a tray holding
up to 50 fibers. The output of the lock-in amplifier is also read into the computer.
This allows us to measure attenuation lengths and relative light yields of various
fibers. A small prototype of the fiber tester has been built and successfully used
to test this technique.
The first role for this set-up will be to evaluate different brands of fiber for light output, attenuation length, and uniformity. After a brand of fiber is chosen for the prototype and the experiment, the tester will be used to characterize each batch of fiber according to attenuation length, so that similar fibers can be used in a given tower and tower-to-tower variations of fiber could be noted for use in calibrations.
Figure: Schematic diagram of the scintillating fiber tester.