7.9 Low-Level Counting
137
7.9.2 Co-incidence Counting System
This type of counting does not decrease the background, but can decrease noise
level produced in the counter due to the heating of some electronic components or
dynode of a photomultiplier tube in the scintillation counting system. Usually, this
unit is used with a scintillation counter for measuring the activity of low energy
β-particulate radiation.
The principle of this unit is based on the fact that the noise level in the two photomultiplier tubes or in any electronic components of the instrument is not produced at
the same time. In this type of counting system, generally two photomultiplier tubes
are separately connected with EHT and amplifier unit. The output of both tubes is
fed to a coincidence unit, which is connected to a pulse height analyzer followed by
a scaler. The sample to be counted is put in between the two photomultiplier tubes.
If photons are seen by both the photomultiplier tubes, the coincidence unit allows
the pulses generated by these tubes to be analyzed by the pulse height analyzer, else
it is rejected. This way noise produced in the photomultiplier tubes or in amplifier
units is eliminated from being recorded. The elimination of noise level is essential
for counting samples like
14 C and
3 H. The efficiency of
14 C counting can be achieved
as high as 80% and that of
3 H 50% by such coincidence counting system.
Summary
In this chapter, we learnt some special techniques and detection systems for
measuring radioactivity for special purposes. These techniques would be useful when dealing with studies of some nuclear reactions and identification of
the products formed in a very small number. From a public health protection
point of view, we have to ascertain that milk, food, or air are not contaminated
with radioactive materials either due to some accidents that occurred in nuclear
thermal power plants, or due to some nuclear explosion for military applications. For such purposes, we need a counter which can measure activity in the
range of a few fractions of a microcurie. We saw the type of counters available
for this purpose. In many nuclear reactions, we face the problem of analyzing α-particles. This type of counting can be done effectively with solid-state
detectors. We also learn about the separation of the radioactive isotopes from
a mixture of radioactivity present in a sample by the radio-chromatography
technique and the techniques to evaluate the efficiency of the separation technique.
137
7.9.2 Co-incidence Counting System
This type of counting does not decrease the background, but can decrease noise
level produced in the counter due to the heating of some electronic components or
dynode of a photomultiplier tube in the scintillation counting system. Usually, this
unit is used with a scintillation counter for measuring the activity of low energy
β-particulate radiation.
The principle of this unit is based on the fact that the noise level in the two photomultiplier tubes or in any electronic components of the instrument is not produced at
the same time. In this type of counting system, generally two photomultiplier tubes
are separately connected with EHT and amplifier unit. The output of both tubes is
fed to a coincidence unit, which is connected to a pulse height analyzer followed by
a scaler. The sample to be counted is put in between the two photomultiplier tubes.
If photons are seen by both the photomultiplier tubes, the coincidence unit allows
the pulses generated by these tubes to be analyzed by the pulse height analyzer, else
it is rejected. This way noise produced in the photomultiplier tubes or in amplifier
units is eliminated from being recorded. The elimination of noise level is essential
for counting samples like
14 C and
3 H. The efficiency of
14 C counting can be achieved
as high as 80% and that of
3 H 50% by such coincidence counting system.
Summary
In this chapter, we learnt some special techniques and detection systems for
measuring radioactivity for special purposes. These techniques would be useful when dealing with studies of some nuclear reactions and identification of
the products formed in a very small number. From a public health protection
point of view, we have to ascertain that milk, food, or air are not contaminated
with radioactive materials either due to some accidents that occurred in nuclear
thermal power plants, or due to some nuclear explosion for military applications. For such purposes, we need a counter which can measure activity in the
range of a few fractions of a microcurie. We saw the type of counters available
for this purpose. In many nuclear reactions, we face the problem of analyzing α-particles. This type of counting can be done effectively with solid-state
detectors. We also learn about the separation of the radioactive isotopes from
a mixture of radioactivity present in a sample by the radio-chromatography
technique and the techniques to evaluate the efficiency of the separation technique.