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6 Scintillation Counter
X -ray photons produced by the internal conversion can be forcefully absorbed by
a suitable screen separating the source from the detector.
• If radio-nuclide decays by emitting several γ -rays, it is necessary to account for
each of them and correct the count rate obtained for any coincidence of these two
γ -rays (as is the case with Cobalt-60 isotope). All these methods need to be applied
only if absolute count rate is required. When relative activity of the samples are
required, like in study of the rate of adsorption of a radioactive isotopes on a
substrate, finding activities of two layers in the solvent extractions, etc., then there
is no need to carry out these corrections, as the contribution of other radiations
would be same in all the samples.
Summary
In this chapter, we learnt about the principle of scintillation counter. We learnt
that photomultiplier tube is used to measure the photons emitted by the scintillator when particulate or electromagnetic radiations interact with phosphor.
Phosphor used for γ -rays counting is normally NaI(Tl) and for particulate
radiation either liquid or solid organic phosphors are preferred. We also learnt
about the types of liquid scintillator and their composition and effect of sample size on the counting efficiency. Some special type of scintillator like gel
scintillator and counting by using filter paper have also been discussed. Precautions needed in counting liquid samples, corrections for chemical, which
quenches photons produced during scintillation, are also emphasized. Finally,
precautions needed in counting radioactive isotopes emitting more than two
types of radiations are also discussed.
6 Scintillation Counter
X -ray photons produced by the internal conversion can be forcefully absorbed by
a suitable screen separating the source from the detector.
• If radio-nuclide decays by emitting several γ -rays, it is necessary to account for
each of them and correct the count rate obtained for any coincidence of these two
γ -rays (as is the case with Cobalt-60 isotope). All these methods need to be applied
only if absolute count rate is required. When relative activity of the samples are
required, like in study of the rate of adsorption of a radioactive isotopes on a
substrate, finding activities of two layers in the solvent extractions, etc., then there
is no need to carry out these corrections, as the contribution of other radiations
would be same in all the samples.
Summary
In this chapter, we learnt about the principle of scintillation counter. We learnt
that photomultiplier tube is used to measure the photons emitted by the scintillator when particulate or electromagnetic radiations interact with phosphor.
Phosphor used for γ -rays counting is normally NaI(Tl) and for particulate
radiation either liquid or solid organic phosphors are preferred. We also learnt
about the types of liquid scintillator and their composition and effect of sample size on the counting efficiency. Some special type of scintillator like gel
scintillator and counting by using filter paper have also been discussed. Precautions needed in counting liquid samples, corrections for chemical, which
quenches photons produced during scintillation, are also emphasized. Finally,
precautions needed in counting radioactive isotopes emitting more than two
types of radiations are also discussed.