358
properties of radionuclides while emitting ionizing radiation. All the elements above
the ordinal number 82 (lead) are unstable because the repulsive forces of the protons
are no longer sufficient neutrons as equilibrium. The lead isotopes
206
Pb,
207
Pb and
208
Pb are the heaviest known stable atom, so lead is also the heaviest stable element
of the periodic table. With the isotope 208Pb, the so-called double magic number is
present in the nucleus. Lead isotopes are the end products of three of the four natural
series of decays of radioactive elements. In this way, a relatively large amount of
lead was formed, due to which there is a relatively large amount of lead in the
Earth’s crust in relation to other heavy metals (mercury, gold, etc.). Namely, the
concentration of protons in one place is too high.
The nucleus of a radionuclide disintegrates spontaneously, passing into another
nucleus. During decay, the nucleus of a radionuclide emits particles and/or electromagnetic rays of short wavelength. Emitted particles and electromagnetic rays are
called ionizing radiation by one name. It is a phenomenon of radioactivity, and the
process itself is transmutation, i.e. spontaneous transition from one nucleus to
another, called radioactive decay.
A nuclide is an atom of a chemical element for which not only the ordinal or
atomic number Z is accurately known but also the total number of nucleons (protons
and neutrons) in the atomic nucleus. There are only 92 chemical elements in nature
and another 12 artificially produced, and about 3100 different nuclides are known,
of which 350 are natural and 2750 are artificial. Most nuclides are unstable (radioactive), about 2800. A suitable combination of protons and neutrons makes the
atomic nucleus stable; as soon as it is different, the nucleus tends to approach a
stable configuration by ejecting the nucleon. The energy levels in the core are
replenished in order to reach the minimum energy configuration, that is, the maximum stability.
12.1.4 Isotope Applications in Analytics
There are several applications, which use the properties of different isotopes of a
given element. One of the most common applications is a tracer or marker in a technique called isotope labelling (Kelly et al. 2005; Rossmann et al. 2000; Richards
et al. 2003; Rhodes et al. 2010; Carter et al. 2015; Rees et al. 2016). Isotopes of a
given element cannot be distinguished from each other by chemical methods.
However, they can be distinguished by the use of physicochemical methods, such as
mass spectrometry (direct differences in mass), infrared spectroscopy (based on
vibrational frequencies in the molecule – heavier isotopes vibrate at lower frequencies than lighter ones), nuclear magnetic resonance, based on different gyromagnetic ratios, etc. Isotopic modification can also be used to determine the mechanisms
of reaction through the kinetic isotope effect (Barling and Weis 2012). In addition
to isotope labelling, several types of spectroscopy use the unique nuclear properties
of specific isotopes. For example, nuclear magnetic resonance (NMR) spectroscopy
can only be used for nonzero nuclear spin isotopes. The isotopes most commonly
L. Fan et al.
properties of radionuclides while emitting ionizing radiation. All the elements above
the ordinal number 82 (lead) are unstable because the repulsive forces of the protons
are no longer sufficient neutrons as equilibrium. The lead isotopes
206
Pb,
207
Pb and
208
Pb are the heaviest known stable atom, so lead is also the heaviest stable element
of the periodic table. With the isotope 208Pb, the so-called double magic number is
present in the nucleus. Lead isotopes are the end products of three of the four natural
series of decays of radioactive elements. In this way, a relatively large amount of
lead was formed, due to which there is a relatively large amount of lead in the
Earth’s crust in relation to other heavy metals (mercury, gold, etc.). Namely, the
concentration of protons in one place is too high.
The nucleus of a radionuclide disintegrates spontaneously, passing into another
nucleus. During decay, the nucleus of a radionuclide emits particles and/or electromagnetic rays of short wavelength. Emitted particles and electromagnetic rays are
called ionizing radiation by one name. It is a phenomenon of radioactivity, and the
process itself is transmutation, i.e. spontaneous transition from one nucleus to
another, called radioactive decay.
A nuclide is an atom of a chemical element for which not only the ordinal or
atomic number Z is accurately known but also the total number of nucleons (protons
and neutrons) in the atomic nucleus. There are only 92 chemical elements in nature
and another 12 artificially produced, and about 3100 different nuclides are known,
of which 350 are natural and 2750 are artificial. Most nuclides are unstable (radioactive), about 2800. A suitable combination of protons and neutrons makes the
atomic nucleus stable; as soon as it is different, the nucleus tends to approach a
stable configuration by ejecting the nucleon. The energy levels in the core are
replenished in order to reach the minimum energy configuration, that is, the maximum stability.
12.1.4 Isotope Applications in Analytics
There are several applications, which use the properties of different isotopes of a
given element. One of the most common applications is a tracer or marker in a technique called isotope labelling (Kelly et al. 2005; Rossmann et al. 2000; Richards
et al. 2003; Rhodes et al. 2010; Carter et al. 2015; Rees et al. 2016). Isotopes of a
given element cannot be distinguished from each other by chemical methods.
However, they can be distinguished by the use of physicochemical methods, such as
mass spectrometry (direct differences in mass), infrared spectroscopy (based on
vibrational frequencies in the molecule – heavier isotopes vibrate at lower frequencies than lighter ones), nuclear magnetic resonance, based on different gyromagnetic ratios, etc. Isotopic modification can also be used to determine the mechanisms
of reaction through the kinetic isotope effect (Barling and Weis 2012). In addition
to isotope labelling, several types of spectroscopy use the unique nuclear properties
of specific isotopes. For example, nuclear magnetic resonance (NMR) spectroscopy
can only be used for nonzero nuclear spin isotopes. The isotopes most commonly
L. Fan et al.