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†
Stable
Relative
Mole
isotope
atomic mass
fraction
142
Nd
141.907 73
0.271 53
143
Nd
142.909 82
0.121 73
144
†
Nd
143.910 09
0.237 98
145
Nd
144.912 58
0.082 93
146
Nd
145.913 12
0.171 89
148
Nd
147.916 90
0.057 56
150
†
149.920 90
0.056 38
Nd
Radioactive isotope having a relatively long
half-life and a characteristic terrestrial
isotopic abundance that contributes
significantly and reproducibly to the
determination of the standard atomic
weight of the element in normal materials.
The half-lives of 144Nd and 150Nd are
2.1 × 1015 years and 8 × 1018 years,
respectively.
Neodymium isotopes in geochronology
143
Nd is a radiogenic isotope produced by decay of 147 Sm, with half-life of 1.06 × 1011 years.
Thus, the isotope-amount ratio n(143Nd)/n(144Nd) can be used for dating rocks on long time
scales and as a chemical tracer in geochemistry (Figure 1) [429, 430]. The very small
accumulation of 142Nd in billion-year-old metamorphosed rocks (alteration of rock structure by
heat or pressure) from Greenland [from the relatively short-lived (~68 × 106 years) alpha decay
of 146 Sm] provided evidence that the crust of the Earth formed before the young planet was more
than 100 million years old.
This is because only a short amount of time could have elapse to incorporate the 146Sm parent
radionuclide into the ancient Greenland minerals before it decayed [431, 432].
Fig. 1: Cross plot of n(143Nd)/n(144Nd) isotope-amount ratio and n(147Sm)/n(144Nd) mole ratio for
two periods of scheelite (calcium tungstate; ore of tungsten) mineralization (metamorphism)
(modified from [430]). 143Nd is produced by decay of 147Sm. Rock containing higher amounts of
147
Sm at time of mineralization will over time produce higher amounts of 143Nd (e.g., sample stage 3
K1 shear zone and sample stage 4 K2). Alternatively, rocks containing lower amounts of 147Sm at
time of mineralization will over time produce lower amounts of 143Nd (e.g., sample stage 3 K1 gneiss
and sample Brl). Samples from an older mineralization event will have proportionally more 143Nd
because of the longer accumulation time for 143Nd; thus, the slope of the line through the bluishfluorescent scheelites with an age of 319 ± 34 million year has a substantially higher slope than the
line through the whitish-bluish-fluorescent scheelites with an age of 29 ± 17 million years. These
lines from which age of mineralization (crystallization) can be determined are called isochrons.
Neodymium isotopes used as a source of radioactive isotope(s)
Nd is being studied for possible use in the production of 147Pm, via the 146 Nd (n, γ) 147Nd →
147
Pm reaction, which is a radioisotopic power-generation source [433, 434].
146
Glossary
alpha decay (α-decay) – radioactive decay process resulting in emission of alpha particles.
[return]
alpha particle – a positively charged nuclear particle identical with the nucleus of a helium atom
consisting of two protons and two neutrons.
atomic number (Z) – The number of protons in the nucleus of an atom.
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]. [return]
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]
isochron – a line indicating age of formation of a suite of rock or mineral samples on a cross plot
of amount ratios of isotopes of the same element and mole ratios of isotopes of different
elements (one of which is radioactive and decays to an isotope of the other element). The time
formed can indicate time since metamorphism, crystallization, shock events, differentiation of
precursor melts, etc. For examples, see neodymium Figure 1, samarium Figure 1, rhenium Figure
1, and osmium Figure 2. [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.
isotopic abundance (mole fraction or amount fraction) – 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]
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].
normal material – a reasonably possible source for an element or its compounds in commerce,
for industry or science; the material is not itself studied for some extraordinary anomaly and its
mole fractions (isotopic abundances) have not been modified significantly in a geologically brief
period [4]. [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).
parent radionuclide – a radioactive isotope, commonly in a radionuclide generator, that decays
to produce a radioactive daughter. For example, the parent radionuclide 99Mo decays to 99mTc,
which is used in radionuclide angiography. [return]
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). [return]
radiogenic – produced by the decay of a radioactive isotope, but which itself may or may not be
radioactive. [return]
radionuclide angiography (also called gated equilibrium blood pool imaging) – a test using
the radioactive isotope 99mTc to evaluate the function of the right and left ventricles of the heart
by measuring radioactivity over the anterior chest as the radioactive blood flows through the
large vessels and the heart chambers.
stable isotope – an atom for which no radioactive decay has ever been experimentally measured.
standard atomic weight – an evaluated quantity assigned by the IUPAC Commission on
Isotopic Abundances and Atomic Weights (CIAAW) to encompass the range of possible atomic
weights of a chemical element that might be encountered in all samples of normal terrestrial
materials. It is comprised of either an interval (currently for 12 elements) or a value and an
uncertainty (a standard Atomic-weight uncertainty), and currently there are 72. A standard
atomic weight is determined from an evaluation of peer-reviewed scientific publications. [return]
tracer - substance used for tracking purposes. [return]
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.
References
4.
C. Kendall, and Coplen, T.B. Hydrological Process. 15, 1363 (2011). 10.1002/hyp.217
429. M. T. McCullocha, and Perfita, M.R. Earth and Planetary Science Letters. 56, 167
(1981).
430. R. H. R. Eichhorn, E. Jagoutz, and U. Schärer. Geochimica et Cosmochimica Acta. 61
(23), 5005 (1997).
431. M. G. Jackson, Hart, S.R., Koppers, A.A.P., Staudigel, H., Konter, J., Blusztajn, J., Kurz,
M., and Russell, J.A. Nature. 448, 684 (2007).
432. G. Caro, Bourdon, B., Birck, J. L., and Moorbath, S. Nature. 423, 428 (2003).
433. T. S. I. Inc. Neodymium Isotopes. Trace Sciences International Inc. 2014 Feb. 27.
http://www.tracesciences.com/nd.htm
434. C. S. Lee, Wang, Y.M., Cheng, W.L., and Ting, G. Journal of Radioanalytical and
Nuclear Chemistry. 130 (1), 21 (1988).
703. I. U. o. P. a. A. Chemistry. Compendium of Chemical Terminology, 2nd ed. (the "Gold
Book"). Blackwell Scientific Publications, Oxford (1997).
706. Coplen. Rapid Communications in Mass Spectrometry. 25 (2011).