Table 12 Properties of several scintillators of Saint Gobain: BC-420, BC-404, BC-408 and the J-PET
scintillator [12].
Properties
BC-420
BC-404
BC-408
J-PET
Light output
[% of Anthracene]
64
68
64
64
Rise time [ns]
0.5
0.7
0.9
0.5
Decay time [ns]
1.5
1.8
2.1
1.9
Maximum of emission
wavelength [nm]
391
408
425
404
H:C ratio
1.102
1.107
1.104
1.104
350
400
450
500
550
600
0
20
40
60
80
100
Norm
alized
inte
nsity [
a.u
.]
Wavelength [nm]
BC-408
BC-404
BC-420
J-PET
Figure 40 Emission spectra of BC-408 (green dashed - dot line), BC-404 (red dashed line), BC-420 (black dotted
line) and J-PET scintillator (violet solid line).
77
Regarding the emission spectra of the considered scintillators, the best matching to
the quantum efficiency wavelength dependency of silicon photomultipliers is achieved for
BC-408 scintillator. According to Fig. 15, the highest quantum efficiency is for around
450 nm. However, having in mind further application in the detectors relying on the signals
time measurements, one has to carefully look also at the timing properties of the
scintilators, for which the BC-408 is the worst within the group being compared.
Cooperation with worldwide companies, like Saint Gobain [12] or Eljen
Technology [13] indicates that even up to 40 % of purchased scintillator strips contained
optical inhomogeneities visible by the eye or when exposed to UV light. Such defects
disturb isotropic propagation of light in scintillator material and significantly decrease the
light output. Therefore, less amount of scintillation light reaches photoelectric converters
what makes the whole detector less efficient for the radiation and particles detection.
Scintillators containing defects need to be changed for the homogeneous ones,
however the procedure itself takes time. Moreover such method of scintillators preparation
entails a large material waste.
Therefore, the process should be optimized considering assortment of the reactor as
well as condition of polymerization to obtain a large fraction of good quality scintillators
minimizing material waste. That also decreases costs of final product, ready for
application.
Summarizing, with the presented dissertation it has been proven that in the
laboratory conditions it is possible to develop plastic scintillators characterized by the
parameters fulfilling the conditions for further application in J-PET/MR tomography as
well as detectors for particle physics research.
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