6.6 Scintillator
101
is enclosed in a specially designed aluminum cover (Fig. 6.2). So far the bottom
surface is concerned, i.e., the side (B) has to be exposed to the photomultiplier tube.
Hence, this side should be transparent. For this reason, a quartz (optically flat) plate
is used to seal the bottom of the crystal (B). Because of the aluminum cover (A) over
the crystal, weak β-particles or α-particles cannot be counted. However, β-particles
of only high energy can be counted by this scintillator, provided its energy is greater
than energy required to penetrate the thickness of the aluminum casing.
6.6.2 Organic Scintillator
Organic scintillator is made of an organic compound, where the basic structure is
made of carbon atoms. Thus, the probability of interaction of γ -rays with the scintillator is less and, hence, the efficiency of counting γ -rays with organic scintillator
is low. However, β-particles and α-particles can be counted with a greater efficiency
due to higher probability of their interaction with the scintillator.
6.6.2.1 Organic Liquid Scintillator
Organic liquid scintillator consists of an organic scintillator, a wavelength shifter,
and a solvent. Particulate radiations (e.g., α-particles or β-particles), present in the
radioactive sample, interact with the scintillator to produce photons. The wavelength
shifter helps to shift the wavelength of the photons to a visible region. These photons
then interact with photomultiplier tube, (as discussed earlier), to produce electrons
which are counted and recorded by the method discussed earlier (Fig. 6.1). Organic
scintillators are normally kept in colored bottle and are always kept under an inert
atmosphere like nitrogen. The liquid scintillator should be kept in a dark bottle, nitrogen atmosphere, and at low temperature, otherwise scintillation properties gradually
diminish. Since such scintillators are made of carbonaceous materials, they can be
useful for counting low energy β-particles or α-particles.
6.6.3 Composition of Scintillator
In the liquid scintillation method, the radioactive material is homogeneously mixed
with one of the scintillator listed below and is kept in a perfectly clean flat bottom
glass vial. This vial is then kept over the photomultiplier tube using some grease
to ensure a good contact of the bottom of the glass vial with the photomultiplier
tube. Since the radioactive sample is homogeneously mixed with the of α-particles
or α-particles or β-particles by the liquid is minimum. Thus, by this technique, liquid
sample can be counted without making a dry source. The solutes and solvents which
are used in a scintillator are listed below
101
is enclosed in a specially designed aluminum cover (Fig. 6.2). So far the bottom
surface is concerned, i.e., the side (B) has to be exposed to the photomultiplier tube.
Hence, this side should be transparent. For this reason, a quartz (optically flat) plate
is used to seal the bottom of the crystal (B). Because of the aluminum cover (A) over
the crystal, weak β-particles or α-particles cannot be counted. However, β-particles
of only high energy can be counted by this scintillator, provided its energy is greater
than energy required to penetrate the thickness of the aluminum casing.
6.6.2 Organic Scintillator
Organic scintillator is made of an organic compound, where the basic structure is
made of carbon atoms. Thus, the probability of interaction of γ -rays with the scintillator is less and, hence, the efficiency of counting γ -rays with organic scintillator
is low. However, β-particles and α-particles can be counted with a greater efficiency
due to higher probability of their interaction with the scintillator.
6.6.2.1 Organic Liquid Scintillator
Organic liquid scintillator consists of an organic scintillator, a wavelength shifter,
and a solvent. Particulate radiations (e.g., α-particles or β-particles), present in the
radioactive sample, interact with the scintillator to produce photons. The wavelength
shifter helps to shift the wavelength of the photons to a visible region. These photons
then interact with photomultiplier tube, (as discussed earlier), to produce electrons
which are counted and recorded by the method discussed earlier (Fig. 6.1). Organic
scintillators are normally kept in colored bottle and are always kept under an inert
atmosphere like nitrogen. The liquid scintillator should be kept in a dark bottle, nitrogen atmosphere, and at low temperature, otherwise scintillation properties gradually
diminish. Since such scintillators are made of carbonaceous materials, they can be
useful for counting low energy β-particles or α-particles.
6.6.3 Composition of Scintillator
In the liquid scintillation method, the radioactive material is homogeneously mixed
with one of the scintillator listed below and is kept in a perfectly clean flat bottom
glass vial. This vial is then kept over the photomultiplier tube using some grease
to ensure a good contact of the bottom of the glass vial with the photomultiplier
tube. Since the radioactive sample is homogeneously mixed with the of α-particles
or α-particles or β-particles by the liquid is minimum. Thus, by this technique, liquid
sample can be counted without making a dry source. The solutes and solvents which
are used in a scintillator are listed below