a - the Greek symbol
for alpha, used to symbolize the fractionation factor.
b - the Greek symbol
d - the Greek lower
case symbol for delta, used for light isotopes to designate
per mil () deviation from a standard.
D - the Greek upper
case symbol for delta, used as the measurement of the
difference between a product and a reactant.
d - the symbol used for deuterium excess,
defined as the intercept of the meteoric water line
(MWL): dD = 8 d18O
D - used as an abbreviation for deuterium (2H).
dD is the variation of
1H and 2H
relative to SMOW.
e - the Greek symbol
for epsilon. Used as the per 104
deviation of sample from a standard. Also used in fractionation
studies to symbolize enrichment.
e - electron
l - the Greek symbol
for lambda, the symbol used to express the decay constant
(rate of radioactive decay) of a nuclide.
n - neutron
p - proton
abundance - the amount of an isotope of an element
that exists in nature, usually expressed in relative
terms as a percentage of the total amount of all isotopes
of the element.
alpha decay - a type of radioactive decay in
which an a particle (two
protons and two neutrons) is emitted from the nucleus
of an atom.
alpha particles - positively charged particles
that consist of two protons and two neutrons (i.e.,
the nucleus of a helium atom), that may be emitted during
amu - atomic mass units; see atomic mass.
anthropogenic - resulting from human activities.
When applied to isotopes, the term usually refers to
nuclides that are the product of the processing of nuclear
fuels, reactor accidents, and nuclear weapons testing.
atom - a particle of matter consisting of a
positively charged nucleus surrounded by a system of
electrons, that cannot be reduced by chemical reaction
atomic mass - the mass of a nucleus in atomic
mass units (amu), based on a standard of 12.00000 for
Syn. atomic weight.
atomic number - number of protons in the nucleus
of an atom; the number determines the element's position
on the periodic table. All isotopes of an element have
the same atomic number
atomic weight - See atomic mass.
beta decay - type of radioactive decay in which
an electron or positron is emitted from the nucleus
of an atom. The emission of an electron results in an
increase by 1 of the atomic number; emission of a positron
results in the atomic number decreasing by 1.
beta particles - high-speed electrons or positrons,
especially those emitted in radioactive decay.
cosmogenic - resulting from cosmic ray activity
in the upper atmosphere. In reference to isotopes, this
refers to those produced through spallation or from
the shattering of a nucleus by cosmic rays. See also
daughter - the product isotope of radioactive
decay; the parent and daughter atoms are of two different
decay constant - the rate of radioactive decay
of a nuclide, expressed by l (chance
delta - the lowercase delta symbol, d,
is used for (per mil) deviation from a standard;
whereas uppercase delta, D,
is used as the measurement of the difference between
a product and a reactant.
electron capture - a radioactive decay process
in which an electron is spontaneously incorporated into
a nucleus; the atomic number of the atom decreases by
electron - an atomic particle that is negatively
charged and has a mass that is .00055 the mass of a
epsilon - the epsilon symbol, e,
expresses per 104
deviation of sample from a standard; it is also used
in fractionation studies to symbolize enrichment.
equilibrium fractionation - fractionation that
occurs between two different phases that are in equilibrium,
e.g., the transformation of water vapor to liquid precipitation.
Although the process is in equilibrium, the rate of
exchange for each isotope is different so that the result
is an enrichment of one of the isotopes.
fractionation - During isotopic fractionation,
heavy and light isotopes partition differently between
two compounds or phases. Isotope fractionation occurs
because the bond energy of each isotope is slightly
different, with heavier isotopes having stronger bonds
and slower reaction rates. The difference in bonding
energy and reaction rates are proportional to the mass
difference between isotopes. Thus, light elements are
more likely to exhibit isotopic fractionation than heavy
GMWL - global meteoric water line (GMWL), an
equation defined by Harmon Craig that correlates the
average relationship between 18O
and 2H in
meteoric waters throughout the world as follows: d2H
= 8 d18O
See meteoric water line.
half-life - the time required for one-half of
a given number of a radionuclide to decay (= t1/2).
is the decay
is the decay equation used to determine half life.
kinetic fractionation - fractionation that is
unidirectional, where equilibrium is not attained. This
type of fractionation applies to evaporation of surface
waters and to most biogeochemical reactions, where the
light isotope is faster reacting and becomes concentrated
in the products.
lithogenic - refers to isotopes produced at
the surface of the earth by direct cosmic ray irradiation
of atoms in solid geologic materials.
mass number - total mass of an atom; the sum
of neutrons and protons.
mass spectrometry - an analytical method used
to identify chemical substances by ionizing the material,
focusing the resulting ions into a beam, then separating
them according to the ratios of their mass to their
net electric charge
meteoric water line (MWL) - the relationship
between 18O and 2H
in meteoric water. Local meteoric water lines are calculated
for given areas; variations from this model are due
to isotope effects of kinetic fractionation.
neutron - atomic particles that have no charge
and have a mass number of 1.
noble gases - the chemically inert elements
of the helium group of the periodic table. The noble
gas family consists of six different elements, five
of which have stable isotopes (helium, neon, argon,
krypton, and xenon), and one that has only radioactive
nuclide -a specific isotope of an atom
proton - an atomic particle that is positively
charged and has a mass number of 1.
radioactive decay - the spontaneous emission
of charged particles from the nucleus of an unstable
atom in order to produce a stable nucleus.
radioactive isotope/nuclide - an isotope that
undergoes radioactive decay.
radiogenic - formed by nuclear processes such
as neutron capture or spallation.
radionuclide - a radioactive isotope; an isotope
that undergoes radioactive decay.
redox - oxidation-reduction; a class of reversible
chemical reactions in which one compound is oxidized
and the other is reduced.
SMOW - the standard mean of ocean water; a standard
used to compare oxygen and hydrogen isotopic compositions
of water in parts per thousand deviation from the mean
value of 18O/16O
and 2H/H in seawater.
spallation reaction - the splitting of atoms
in the upper atmosphere through the bombardment of cosmic
rays. This results in the formation of new, often unstable,
isotopes. Spallation reactions occur in the upper atmosphere
when cosmic rays hit gas molecules and also at the surface
of the earth by direct cosmic ray irradiation of atoms
in solid geological materials.
stable isotopes - isotopes not subject to radioactive
decay, whose mass does not change over time.