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Stable
isotope
107
Ag
109
Ag
Relative
atomic mass
106.905 09
108.904 755
Mole
fraction
0.518 39
0.481 61
Silver isotopes in Earth/planetary science
The measurement of relative amounts of 107 Ag and 109 Ag is used to study the processes
responsible for the isotopic fractionation of silver isotopes in ore deposits, which depends on
the specific minerals and environmental conditions. This is currently an area of active research
and it is thought that the relative amounts of the isotopes of silver are altered during the
formation of the ore [350, 351].
Silver isotopes in forensic science and anthropology
Silver isotope-amount ratios (n(107 Ag)/n(109 Ag)) along with isotope-amount ratios of copper
(n(65Cu)/ n(63Cu)), and isotope-amount ratios of lead (n(206 Pb)/ n(204 Pb), n(207Pb)/ n(204 Pb) and
n(208Pb)/ n(204 Pb)) have been used to determine origins of European coins and information on the
flow of goods in the world market over time (Figure 1). Metals from Peru and Mexico and those
from European mining have distinct isotopic signatures that enable the origin of the metal to be
determined by examining the isotopic compositions of silver, copper, and lead in the coins.
Abundant silver sources, mined in Mexico and Peru in the 16th century, were used to mint coins,
but they were not a major influence in the European coin market until the 18th century (Figure 1)
[232].
Fig. 1: Cross plot of lead model age and mole fraction 109 Ag of selected coins (modified from
[232]. The isotopic signatures of the silver, copper, and lead in the metals used to make Spanish
coins can be used to trace the origin of the metals to help determine the flow of metal in the
global market during the 16thcentury.
Silver isotopes in geochronology
The isotope-amount ratio n(107 Pd)/ n(107 Ag) is used in geochronology to date major thermal
events in the Solar System. Although 107 Ag is naturally occurring, it is also the daughter
product by beta decay of 107Pd. If both excess 107 Ag and 107 Pd are present in a sample of
extraterrestrial origin, then the material would have formed sometime after 107Pd decayed (i.e.
sometime after the 6.5-million-year half-life of 107 Pd). The isotope-amount ratio n(107 Pd)/
n(107Ag) can be measured to help determine when the 107 Pd decay process began and determine
how much time has elapsed since the material was formed [342, 344-346, 352, 353].
Silver isotopes in industry
Ag is being studied as a possible target for cyclotron production of 103Pd via the 107 Ag (p, α n)
103
Pd reaction. 103Pd releases X-rays and Auger electrons at the rate of about 80 X-rays and 186
Auger electrons per 100 decays of 103Pd, which makes this isotope an ideal candidate for internal
radiotherapy for the treatment of cancers. The production of this isotope in a no-carrier form
(not formed in another solution) is important for its medical uses. By using neutrons, photons,
and charged particles to force reactions with isotopes of a higher mass number than 103, 103 Pd
will occur in a fraction of those reactions. The most common methods of 103 Pd production use
targets of rhodium or other isotopes of palladium. However, 107 Ag has also been studied as a
feasible option [348, 354, 355]. 109Ag can be used to produce the gamma reference source 110mAg
to help calibrate gamma detectors [348, 354, 355].
107
Glossary
atomic number (Z) – The number of protons in the nucleus of an atom.
Auger electrons – electron that is ejected from an atom when an inner-shell electron is lost and
an electron with a higher energy level takes its place. The excess energy is carried off by the
electron and no photon is emitted in the process. [return]
beta decay (β-decay) – radioactive decay process resulting in emission of a beta particle of
either positive or negative charge (an electron or positron).[return]
cyclotron – an apparatus in which charged atomic and subatomic particles are accelerated by a
rapidly varying (radio frequency) electric field while following an outward spiral path in a
constant magnetic field. [return]
daughter product– (decay product), any nuclide produced by a specified radionuclide (parent)
in a decay chain. [return]
electron – elementary particle of matter with a negative electric charge and a rest mass of about
9.109 × 10–31 kg.
element (chemical element) – a species of atoms; all atoms with the same number of protons in
the atomic nucleus. A pure chemical substance composed of atoms with the same number of
protons in the atomic nucleus [703].
gamma rays (gamma radiation) – a stream of high-energy electromagnetic radiation given off
by an atomic nucleus undergoing radioactive decay. The energies of gamma rays are higher
than those of X-rays; thus, gamma rays have greater penetrating power.
half-life (radioactive) – the time interval that it takes for the total number of atoms of any
radioactive isotope to decay and leave only one-half of the original number of atoms. [return]
isotope – one of two or more species of atoms of a given element (having the same number of
protons in the nucleus) with different atomic masses (different number of neutrons in the
nucleus). The atom can either be a stable isotope or a radioactive isotope.
isotope-amount ratio (r) – amount (symbol n) of an isotope divided by the amount of another
isotope of the chemical element in the same system [706]. [return]
isotopic composition – number and abundance of the isotopes of a chemical element that are
naturally occurring [706]. [return]
isotopic fractionation (stable-isotope fractionation) – preferential enrichment of one isotope
of an element over another, owing to slight variations in their physical, chemical, or biological
properties [706]. [return]
mass number (A) – total number of heavy particles (protons and neutrons, jointly called
nucleons) in the nucleus of an atom [703]. [return]
mole fraction (amount fraction or isotopic abundance) – the amount (symbol n) of a given
isotope (atom) in a sample divided by the total amount of all stable and long-lived radioactive
isotopes of the chemical element in the sample. [return]
neutron – an elementary particle with no net charge and a rest mass of about 1.675 × 10–27 kg,
slightly more than that of the proton. All atoms contain neutrons in their nucleus except for
protium (1H). [return]
photon – elementary particle of electromagnetic radiation carrying energy proportional to the
radiation frequency but with zero electric charge and zero mass. [return]
positron – the antimatter counterpart of the electron, with a mass identical to that of the electron
and an equal but opposite (positive) charge.
proton – an elementary particle having a rest mass of about 1.673 × 10–27 kg, slightly less than
that of a neutron, and a positive electric charge equal and opposite to that of the electron. The
number of protons in the nucleus of an atom is the atomic number.
radioactive decay – the process by which unstable (or radioactive) isotopes lose energy by
emitting alpha particles (helium nuclei), beta particles (positive or negative electrons), gamma
radiation, neutrons or protons to reach a final stable energy state.
radioactive isotope (radioisotope) – an atom for which radioactive decay has been
experimentally measured (also see half-life).
radiotherapy (radiation therapy) – the treatment of disease by means of radiation from
radioactive substances or X-rays. [return]
stable isotope – an atom for which no radioactive decay has ever been experimentally measured.
X-rays – electromagnetic radiation with a wavelength ranging from 0.01 to 10 nanometers—
shorter than those of UV rays and typically longer than those of gamma rays. [return]
References
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354. T. S. I. Inc. Silver Isotopes. Trace Sciences International Inc. 2014 Feb. 26.
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Book"). Blackwell Scientific Publications, Oxford (1997).
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