18
Both monomers: styrene and vinyltoluene are viscous liquids which polymerize on
heating to form of solid, thermoplastic polymers. The basis of all aromatic vinyl polymers,
including polystyrene and polyvinyltoluene, are -CH=CH
2
bounds
which breaking enable
to built long polymeric chains [37].
Polymer cannot be an effective scintillator because of weak fluorescence efficiency
and short mean free path for scintillating light. In molecules
containing aromatic rings,
only
small fraction, about 3 % of the energy is converted into optical photons [38]. The
wavelength of emitted photons is not adjusted to quantum efficiency
of photomultiplier
(see Fig. 5). Polymer is just the medium to transfer the energy to primary fluor.
About 1 wt. % of the dopant increases not only the attenuation length of photons but also
the scintillator light output [33].
There is a large number of chemical compounds, that can be used as primary fluors
in plastic scintillators. Some of them are presented in Tab. 4.
Table 4 Substances that can be used as primary fluors in plastic scintillators. λ
abs
denotes wavelength at maximum
of absorption, λ
em
- wavelength at maximum of emission, Φ
f
- fluorescence quantum efficiency, τ - decay time of
light pulses, R - solubility in a given solvent at 20
o
. Denotation of solvents: mb– toluene, a – acetonitryle, b –
benzene, c – cyklohexsan, d – dioxane, e – ethanol, k – xylene, m – methylene chloride, me – methanol, t – THF.
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