Physics and Engineering of Radiation Detection

6.2. Organic Scintillators 345

Table 6.2.1: Wavelength of maximum emissionλmaxand decay constantτof some
organic plastic scintillators (39).

Liquid λmax(nm) τ(ns)

Polystyrene with 36gm/lofp-terphenyl 355 ≤3.0

Polystyrene with 16gm/lof 1,1,4,4-terphenyl-

1,3-butadiene 450 4.6

Polystyrene with 36gm/lofp-terphenyl and

0.2gm/lof 1,1,4,4-terphenyl-1,3-butadiene 445 4.0

Polyvinyl-toluene with 16gm/lof 1,1,4,4-terphenyl-

1,3-butadiene 450 4.6

Polyvinyl-toluene with 36gm/lofp-terphenyl and

0.2gm/lof 1,1,4,4-terphenyl-1,3-butadiene 445 4.0

6.2.C Liquid Scintillators

There are a number of liquids that produce scintillation light and can therefore
be used in detectors. In general liquid scintillators used in detection systems are
composed of the following three organic components.

Primary Fluor:The primary fluor or primary scintillator is the main scintil-

lator in the mixture. It has high scintillation efficiency but produces light in

the ultraviolet region of the electromagnetic spectrum.

Wavelength Shifter:The UV photons produced by the primary fluor have

short attenuation lengths in the liquid. Since the liquid is not completely

transparent to them therefore most of them can not escape from the material.

The purpose of the wavelength shifter is to shift the wavelength of these photons

to the visible region. The wavelength shifters are also sometimes known as

secondary fluor since they are also scintillators that absorb UV photons and

give off visible light photons. Most of the practical wavelength shifters produce

blue light.

Base Liquid:The above two mentioned scintillators are mixed homogeneously

in a liquid that has good light transmission properties.

Since the basic building blocks of liquid scintillators are essentially similar to
the plastic scintillators, the requirements of purity for their constituents are also
similarly quite stringent. The base, primary fluor and the wavelength shifter, all