33
tight box set-up at CERN. In these experiments, two opposite edges of a sample
were coupled to two Kuraray Y-11(200) optical fibers which were connected to
a standard Tile Calorimeter photomultiplier tube. The fibers were of a 1 mm
diameter and slotted into grooves in the sample holder
in order to ensure more
control over the contact made between the fibers and scintillator edges.
Figure 4-11: Set-up of the light box used to test the light yield.
The
90
Sr source was scanned over the sample in the X-Y direction whilst emitting
its radiation in the Z direction. For each X -Y position of the source, a one second
integrated signal registered by the PMT was recorded. A lead cover was used to
ensure that only interaction with the sample regions were measured. Light yield
experiments were conducted several weeks after irradiation thus providin g time
for partial recovery in the scintillators. Control samples
and irradiated samples
were tested, with three measurements made per sample.
4.2.3.
Fluorescence spectroscopy
The light fluorescence of each plastic scintillator was measured using the
LabRAM HR Raman spectrograph. A 229 nm laser with a power of ~3-5 mW was
34
employed to provide energy for molecular excitations
to occur and thereby
prompt light emission through luminescence. At this wavelength, the laser energy
is sufficient to be absorbed by the PS or PVT base,
and the successive light
transfer from base to primary and secondary fluors can occur. This enables one
to mimic the interaction of energetic particle showers with the plastic
scintillators.
Photographs of the LabRAM HR are shown below. The l aser is guided through a
series of mirrors and optics in the machine, and is incident on the sample through
the microscope aperture.
As the sample fluoresces, the light emitted in the
direction back up the aperture is collected by a detector and a differen tial
wavelength spectrum is obtained.
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