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

Figure 5-1: EJ208 samples irradiated to doses of ~80 MGy, 25 MGy, 8 MGy and 0.8 MGy 
from left to right. 
Figure 5-2: Fading of discolouration observed in ~25 MGy irradiated EJ208 samples.

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It was also observed that samples irradiated to doses of 25 MGy and higher 
became more rigid and brittle. Due to their small sizes, samples were handled 
with tweezers during placement and removal from holders. Samples were easily 
scratched and care had to be taken when handling them. The scintillators were 
handled along their corners and edges in order to prevent scratches over the 
irradiated regions.
5.2.
 
Results of the light transmission 
The light transmission spectra with respect to air, for all the tested samples over 
several days, are shown in Appendix C. At the high wavelengths, ~10-20% of the 
transmission loss is typically due to reflections at the sample interface. Small 
fluctuations in the data may be due to systematics arising from different 
placement of the scintillators or surface scratches formed through handling. 
These fluctuations fall within 3 sigma of the average, leading to a maximum of 
5% uncertainty in the data.
5.2.1.
 
Features in the transmission spectra 
All the un-irradiated blue emitting scintillators have an absorption edge starting 
at ~410 nm, which completely falls off at around 320 -330 nm. Within this 
absorptive edge region, additional absorption peak features (observed as 
transmission dips) are present and vary for the different types of scintillators. 
This wavelength region corresponds to where light absorption by the secondary 
fluors are expected. 
The PVT based EJ200, EJ208 and BC408 each have a peak at ~350 nm and their 
spectra show similar features. The UPS923A and Tilecal types also have similar 
features to each other, due to their structural similarity, and show peak features 
at ~350 nm, 365 nm and 385 nm. EJ260, which is the green emitting scintillator, 
has its fall-off region starting around 475 nm, with complete absorption occurri ng 
below 350 nm. Additional absorption features occur at ~430nm and 455 nm.

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After irradiation, the formation of similar features are observed in the respective 
spectra of the various sample types. For the lowest administered dose of ~0.8 -1 
MGy, changes to the absorptive features in the fall-off regions occur. In