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

3.3.
 
Description of plastic scintillators under study 
Four commercial plastic scintillators (EJ200, EJ208, EJ260 and BC408) and two 
types employed by the ATLAS detector (UPS923A and TileCal) were 
investigated. The plastics are composed of either a polyvinyl to luene (PVT) or 
polystyrene (PS) base. Polyvinyl toluene consists of long chains of vinyl toluene 
molecules which comprise of a benzene ring bonded to a methyl group (CH
3
) and 
a vinyl group (CH
2
-CH-).
Polystyrene consists of long chains of styrene monomers . Styrene is very similar 
to vinyl toluene except that it does not contain a methyl group. In both polymers, 
the benzene ring gives rise to the delocalized π-electrons. All the scintillators 
investigated were blue emitting, with the exception of EJ260 whic h emits light 
in the green wavelength region. Details on their composition and properties are 
listed in the Table 3-1. 
Figure 3-4: Photographs of plastic scintillators under study

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Table 3-1: Table summarising the various properties of the scintillators under study.
Scintillator 
EJ200 
EJ208 
EJ260 
BC408 
UPS923A 
Protvino 
Manufactured by: 
Eljen 
Technology 
Eljen 
Technology 
Eljen 
Technolog
y 
Saint Gobain 
Crystals 
Institute of 
Scintillating 
Materials, 
Kharkiv. 
(Used 
in 
MBTS) 
Institute of High 
Energy Physics 
(IHEP), 
Protvino 
in 
association with 
SIA 
luch, 
Podolsk. 
(Used in Tile 
Barrel) 
Base 
PVT 
PVT 
PVT 
PVT 
PS 
PS 
Primary Fluor 
0.3% 
organic 
fluors 
0.3% 
organic 
fluors 
0.3% 
organic 
fluors 
Not available 
(However, 
listed 
as 
a 
performance 
equivalent of 
EJ200) 
2% PTP 
1.5% PTP 
Secondary Fluor 
0.03% 
POPOP 
0.044% 
POPOP 
Light Output, % 
Anthracene 
64 
60 
60 
64 
60 
Not available 
Wavelength 
of 
Max. 
Emission, 
nm 
425 
435 
490 
425 
425 
Rise Time, ns 
0,9 
1 
~ 
0,9 
0,9 
Decay Time, ns 
2,1 
3,3 
9,2 
2,1 
3,3 
Density, g/cc: 
1,023 
1,023 
1,023 
1,032 
1,06 
Refractive Index 
1,58 
1,58 
1,58 
1,58 
1,6 
Light 
attenuation 
length (cm) 
~400* 
~400* 
~400* 
380** 
400 
Source 
[21] 
[22] 
[23]
[24] 
*In a cast sheet of dimensions 2 cm x 20 cm x 300 cm
**In a cast sheet of dimensions 1 cm x 20 cm x 200 cm

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The Protvino type plastic scintillators were manufactured specifically for the Tile 
Calorimeter using an injection molding technique. The design of the scintillator 
was specifically geared towards cutting cost of manufacture since these 
scintillators were to be used in the barrels and would require a large quantity of 
material. In comparison to a similar Bicron RH4 cast scintillator, the Protvino 
scintillator yielded ~2.5 times less light in response to ~3 MeV minimum ionizing 
beta particles from a Ru
106
source [25].
Studies were also conducted by the Institute of High Energy Physics (IHEP) team, 
into the effect of changing concentration of the fluors. For an increase in PTP 
concentration from 0.1% to 0.2%, the light output increased by 10% , whilst an 
increase in concentration of POPOP from 0.02% to 0.1% had little effect on light 
yield [24]. Since UPS923A scintillators are very similar in composition to the 
Protvino type, with the exception of different concentrations of fluors, we can 
assume that they are the better performing of the two in terms of light response. 
UPS923A is marketed by the manufacturer as being a good general purpose 
scintillator with good transparency.
EJ200 and BC408 are recommended by their respective manufacturers, for use in 
time of flight systems which require large area coverage due to their short rise 
and decay times. They also have the highest light output from the 6 scintillators 
investigated.
EJ208 has a longer emission wavelength than EJ200, and is ideal for systems in 
which uniformity of light collection is of utmost importance, whilst timing takes 
a secondary priority. In addition, EJ208 is predicted to offer greater tolerance 
against radiation damage since damage results in the increased optical attenuation 
of light at shorter wavelengths.
EJ260 has the longest emission wavelength and shifts light to the green spectrum. 
It is therefore proposed to offer greater radiation tolerance than conventional blue 
emitting plastic scintillators and can still be coupled to common blue sensitive 
phototubes.

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