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

2.2.
 
Plastic scintillators in the Tile Calorimeter 
The Tile Calorimeter [7] (TileCal) is the hadronic calorimeter of ATLAS [5]. It 
is a sampling calorimeter, using steel as the absorber medium and scintillator 
tiles as the active medium. It is responsible for measuring the energy and tracks 
of hadrons, taus and jets and was designed to contain all hadronic showers 
developing from the p-p collisions. It also contributes to the reconstruction of 
missing transverse energy. A zoomed view into the Calorimeter region of the 
ATLAS detector is shown Figure 2-3.  
Figure 2-3: Diagram depicting the ATLAS calorimeter regions. 
2.2.1.
 
The Barrel regions 
The TileCal consists of a central long barrel (LB) flanked on either side by 
extended barrels (EB). Each barrel consists of 64 modules stacked azimuthally, 
resulting in a cylindrical structure of inner radiu s 2.23 m and outer radius 4.23 
m. The LB modules cover the region
0 < |𝜂| < 0.8
, whilst the EB modules cover 
the region
0.8 < |𝜂| < 1.7
.

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Each module consists of a matrix of 3 mm thick scintillator t iles sandwiched 
between 4 mm thick steel plates arranged perpendicular to the beam pipe. The 
scintillator tiles are arranged in 11 rows and vary in size.
As a high energy hadron passes through the tile modules, it interacts with the 
atomic nuclei of the steel absorber, to produce a shower of lower energy particles. 
These interact with the scintillator tiles which absorb energy from the incoming 
particles and fluoresce to emit light.
The scintillation light is collected by wavelength shifting (WLS) optical fibers 
coupled along two of the exposed tile edges. Currently, Y11 fibers obtained from 
Kuraray are employed. The fibers are arran ged in plastic profiles to ensure 
contact with individual tiles.
Tiles are grouped into readout cells and the fibers of these are bundled together 
in Lucite tubes. The cells are segmented into three longitudinal layers, (A, BC 
and D) which are approximately 1.4, 4.0 and 1.8 interaction lengths thick 
respectively at
𝜂 = 0
. The cells are numbered according to the pseudorapidity 
range that it covers, with A and BC cells numbered in pseudorapid ity intervals 
of 0.1 and D cells in intervals of 0.2 [8]. The cell segmentation for the LB and 
EB modules is shown in Figure 2-5.  
An LB module contains 337 scintillator tiles per row, leading to a total of 3377 
tiles. An EB module contains 1591 scintillating tiles. The fiber bundles are 
coupled to photomultiplier tubes (PMT), and light detected by the PMT’s 
generate a signal. Tiles are wrapped in Tyvek paper and fibers are aluminized on 
the ends which are not coupled to the PMT’s, in order to maximise the amount of 
light collected.
Each cell is read out by two PMT’s, which detect the light from each side of the 
module. This is done for redundancy and to ensure special uniformity. The signal 
generated by the PMT’s is then processed with readout electronics housed in the 
same steel girder as the PMT’s. These then digitize the data which can be 
analysed thereafter [9]. Figure 2-4 shows a schematic of a TileCal barrel module.

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