Chapter 9
Factors Affecting the Counting Efficiency
9.1 Introduction
In the previous chapter, we realized the importance of source preparation for getting
meaningful results. However, in addition to source preparation, there are many other
factors, like geometrical factors, scattering of radiation, selection of radiation emitted
by the isotope etc., that also need to be considered for measuring the activity of the
radioactive sample. It is necessary to consider these factors, especially when an
absolute count rate is required. In this chapter, we shall discuss these factors to a
greater depth.
The best way to determine counting efficiency is by counting a sample whose
absolute count rate is known, e.g., x disintegration per minute (abbreviated as x
dpm). Suppliers of the isotope give this information. If the observed count rate of
the isotope (containing x dpm) is y cpm, then the efficiency of counting system is
given by the following equation:
Efficiency
factor
=
Excepted count rate (x dpm) − Observed count rate (y cpm)
Excepted count rate (x dpm)
(9.1)
This procedure is most accurate, simple, and takes care of all possible errors which
might be present in the selected counting procedure and which perhaps may not be
covered in the factors discussed in this chapter. In the foregoing sections, we shall
discuss some of the factors, which can affect the efficiency of the counting process.
9.2 Geometrical Efficiency
In counting system, where the source is mounted outside the sensitive volume of the
counter, such as in the end-window G.M. counter, the efficiency of counting depends
upon the fraction of radiations that pass through the window of the counter. The
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
M. Sharon and M. Sharon, Nuclear Chemistry,
https://doi.org/10.1007/978-3-030-62018-9_9
147
Factors Affecting the Counting Efficiency
9.1 Introduction
In the previous chapter, we realized the importance of source preparation for getting
meaningful results. However, in addition to source preparation, there are many other
factors, like geometrical factors, scattering of radiation, selection of radiation emitted
by the isotope etc., that also need to be considered for measuring the activity of the
radioactive sample. It is necessary to consider these factors, especially when an
absolute count rate is required. In this chapter, we shall discuss these factors to a
greater depth.
The best way to determine counting efficiency is by counting a sample whose
absolute count rate is known, e.g., x disintegration per minute (abbreviated as x
dpm). Suppliers of the isotope give this information. If the observed count rate of
the isotope (containing x dpm) is y cpm, then the efficiency of counting system is
given by the following equation:
Efficiency
factor
=
Excepted count rate (x dpm) − Observed count rate (y cpm)
Excepted count rate (x dpm)
(9.1)
This procedure is most accurate, simple, and takes care of all possible errors which
might be present in the selected counting procedure and which perhaps may not be
covered in the factors discussed in this chapter. In the foregoing sections, we shall
discuss some of the factors, which can affect the efficiency of the counting process.
9.2 Geometrical Efficiency
In counting system, where the source is mounted outside the sensitive volume of the
counter, such as in the end-window G.M. counter, the efficiency of counting depends
upon the fraction of radiations that pass through the window of the counter. The
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
M. Sharon and M. Sharon, Nuclear Chemistry,
https://doi.org/10.1007/978-3-030-62018-9_9
147