Proton induced radiation damage studies on plastic scintillators for the Tile calorimeter of the atlas detector

90
Sr 
The scintillator light yield in response to beta electrons emitted by a 
90
Sr source 
(with average energies of 0.54 MeV and 2.28 MeV) was measured using the light 

---

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.