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

Figure 5-6: 2D mapping of the PMT signal with Sr90 source position, indicating signal 
regions corresponding to regions on the experimental set -up. 
The beta electrons emitted by the source can interact over a 2 mm lateral radius 
from the actual position of the source. Hence the signal obtained for the 1 mm 
diameter fiber spans over ~5 mm. This is similarly observed over the sample 
region. Since samples were tested after irradiation only, the intention was to 
compute the ratio of light loss by taking the ratio between the signal over the 
irradiated spot region and an un-irradiated “corner region” of the same sample.
This however was not an accurate measure due to the large range of the 
interaction of the source. Thus, a control un-irradiated sample for each 
scintillator type had to be tested as well so that a comparison of the loss could be 

---

44 
made. Figure 5-7 shows 3D mappings indicating loss to the light yield signal for 
different irradiation doses of EJ200 samples. Photographs of the sample 
indicating where the corresponding spot regions occur are also shown.
Figure 5-7: 3D mappings of the light yield for several EJ200 samples with different levels 
of proton induced radiation damage.
Three measurements were taken for each sample, with the sample rotated in the 
holder for each measurement. It was observed that the geometry of the sample 
tested played a large impact on the magnitude of the PMT signal measured. This 
is because the amount of light transferred between the scintillator and the fiber 
is dependent on the contact made between the two. Thicker samples therefore 
make a better contact and result in a larger measured signal. The different 
samples also varied slightly in their size, with edge lengths varying by up to 0.3 

---

45 
mm. This further impacted on the signal measured. A comparison betwe en the 
potential systematic variations and their impact on the three measured signals 
tested per sample is drawn in Figure 5-8 for all the TileCal samples tested.