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

Figure 5-5: Relative transmission for the various sample types at their respective 
wavelengths of maximum emission, measured 4 weeks after irradiation.
Studying the transmission loss has given insight into the two possible 
mechanisms responsible for the optical changes observed in radiation damaged 
plastic scintillators. These are; damage to fluors resulting in reduced absorption 
and hence loss of emitted light shifted to higher wavelengths, and the formation 
of free radicals which quench scintillation light. Furthermore, the higher 
wavelength shifting scintillators (EJ260, followed by EJ208) showed the least 
loss in light transmission.
5.3.
 
Results of the light yield studies 
To assess the light yielded by the different radiation damaged scintillator 
samples, their response to a Sr
90
beta electron source was tested. The current 
across a photomultiplier coupled to the scintillator via two fibers, was measured 
as a function of radiation source position. An example of the mapping of this 
Transmission loss at wavelengths of maximum emission
Dose (Gy)
1e+6
1e+7
1e+8
Re
lati
ve
 Trans
missio
n
 (
a.u)
0,0
0,2
0,4
0,6
0,8
1,0
1,2
EJ200 (425 nm)
EJ208 (435 nm)
EJ260 (490 nm)
BC408 (425 nm)
UPS923A (425 nm)
TileCal (425 nm)

---

43 
PMT signal verses source position over a scintillator sam ple is shown in Figure 
5-6.The mapping is correlated to the position of the sample within the set -up 
shown to the right.
A small gap occurs between the sample holder and the lead cove r, leading to a 
region where beta electrons emitted by the Sr90 source interact with the two 
fibers. This is demarcated by the yellow box. The approximate region of the 
sample is demarcated in the brown box. A background signal is obtained by 
averaging over the region within the red box, and is subtracted from the rest of 
the mapping before analysis.