Iodine-129
Encyclopedia
Iodine-129 is long-lived radioisotope of iodine
which occurs naturally, but also is of special interest in the monitoring and effects of man-made nuclear fission decay products, where it serves as both tracer and potential radiological contaminant.
of uranium
and plutonium
in nuclear reactors. Significant amounts were released into the atmosphere
as a result of nuclear weapons testing in the 1950s and 1960s.
It is also naturally produced in small quantities, due to the spontaneous fission of natural uranium
, by cosmic ray spallation
of trace levels of xenon
in the atmosphere, and some by cosmic ray
muon
s striking tellurium-130.
129I decays with a half-life
of 15.7 million years, with low-energy beta
and gamma
emissions, to xenon-129 (129Xe).
s that are produced in significant amounts. Its yield is 0.6576% per fission (U-235
). Larger proportions of other iodine isotopes like 131I
are produced, but because these all have short half-lives, iodine in cooled spent nuclear fuel
consists of about 5/6 129I and 1/6 the only stable iodine isotope, 127I.
Because 129I is long-lived and relatively mobile in the environment, it is of particular importance in long-term management of spent nuclear fuel. In a deep geological repository
for unreprocessed used fuel, 129I is likely to be the radionuclide of most potential impact at long times.
Since 129I has a modest neutron absorption cross-section
of 31 barns
, and is relatively undiluted by other isotopes of the same element, it is being studied for disposal by nuclear transmutation
by re-irradiation with neutron
s or by high-powered lasers.
discovered that certain meteorite
s contained an isotopic anomaly in the form of an overabundance of 129Xe. He inferred that this must be a decay product
of long-decayed radioactive iodine-129. This isotope is produced in quantity in nature only in supernova
explosions. As the half-life of 129I is comparatively short in astronomical terms, this demonstrated that only a short time had passed between the supernova and the time the meteorites had solidified and trapped the 129I. These two events (supernova and solidification of gas cloud) were inferred to have happened during the early history of the Solar System
, as the 129I isotope was likely generated before the Solar System was formed, but not long before, and seeded the solar gas cloud isotopes with isotopes from a second source. This supernova source may also have caused collapse of the solar gas cloud.
Iodine
Iodine is a chemical element with the symbol I and atomic number 53. The name is pronounced , , or . The name is from the , meaning violet or purple, due to the color of elemental iodine vapor....
which occurs naturally, but also is of special interest in the monitoring and effects of man-made nuclear fission decay products, where it serves as both tracer and potential radiological contaminant.
Formation and decay
129I is primarily formed from the fissionNuclear fission
In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts , often producing free neutrons and photons , and releasing a tremendous amount of energy...
of uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
and plutonium
Plutonium
Plutonium is a transuranic radioactive chemical element with the chemical symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, forming a dull coating when oxidized. The element normally exhibits six allotropes and four oxidation...
in nuclear reactors. Significant amounts were released into the atmosphere
Atmosphere
An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...
as a result of nuclear weapons testing in the 1950s and 1960s.
It is also naturally produced in small quantities, due to the spontaneous fission of natural uranium
Natural uranium
Natural uranium refers to refined uranium with the same isotopic ratio as found in nature. It contains 0.7 % uranium-235, 99.3 % uranium-238, and a trace of uranium-234 by weight. In terms of the amount of radioactivity, approximately 2.2 % comes from uranium-235, 48.6 % uranium-238, and 49.2 %...
, by cosmic ray spallation
Cosmic ray spallation
Cosmic ray spallation is a form of naturally occurring nuclear fission and nucleosynthesis. It refers to the formation of elements from the impact of cosmic rays on an object. Cosmic rays are highly energetic charged particles from outside of Earth ranging from protons, alpha particles, and nuclei...
of trace levels of xenon
Xenon
Xenon is a chemical element with the symbol Xe and atomic number 54. The element name is pronounced or . A colorless, heavy, odorless noble gas, xenon occurs in the Earth's atmosphere in trace amounts...
in the atmosphere, and some by cosmic ray
Cosmic ray
Cosmic rays are energetic charged subatomic particles, originating from outer space. They may produce secondary particles that penetrate the Earth's atmosphere and surface. The term ray is historical as cosmic rays were thought to be electromagnetic radiation...
muon
Muon
The muon |mu]] used to represent it) is an elementary particle similar to the electron, with a unitary negative electric charge and a spin of ½. Together with the electron, the tau, and the three neutrinos, it is classified as a lepton...
s striking tellurium-130.
129I decays with a half-life
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...
of 15.7 million years, with low-energy beta
Beta particle
Beta particles are high-energy, high-speed electrons or positrons emitted by certain types of radioactive nuclei such as potassium-40. The beta particles emitted are a form of ionizing radiation also known as beta rays. The production of beta particles is termed beta decay...
and gamma
Gamma ray
Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...
emissions, to xenon-129 (129Xe).
Fission product
129I is one of the 7 long-lived fission productLong-lived fission product
Long-lived fission products are radioactive materials with a long half-life produced by nuclear fission.-Evolution of radioactivity in nuclear waste:...
s that are produced in significant amounts. Its yield is 0.6576% per fission (U-235
Uranium-235
- References :* .* DOE Fundamentals handbook: Nuclear Physics and Reactor theory , .* A piece of U-235 the size of a grain of rice can produce energy equal to that contained in three tons of coal or fourteen barrels of oil. -External links:* * * one of the earliest articles on U-235 for the...
). Larger proportions of other iodine isotopes like 131I
Iodine-131
Iodine-131 , also called radioiodine , is an important radioisotope of iodine. It has a radioactive decay half-life of about eight days. Its uses are mostly medical and pharmaceutical...
are produced, but because these all have short half-lives, iodine in cooled spent nuclear fuel
Spent nuclear fuel
Spent nuclear fuel, occasionally called used nuclear fuel, is nuclear fuel that has been irradiated in a nuclear reactor...
consists of about 5/6 129I and 1/6 the only stable iodine isotope, 127I.
Because 129I is long-lived and relatively mobile in the environment, it is of particular importance in long-term management of spent nuclear fuel. In a deep geological repository
Deep geological repository
A deep geological repository is a nuclear waste repository excavated deep within a stable geologic environment...
for unreprocessed used fuel, 129I is likely to be the radionuclide of most potential impact at long times.
Since 129I has a modest neutron absorption cross-section
Neutron cross-section
In nuclear and particle physics, the concept of a neutron cross section is used to express the likelihood of interaction between an incident neutron and a target nucleus. In conjunction with the neutron flux, it enables the calculation of the reaction rate, for example to derive the thermal power...
of 31 barns
Barn (unit)
A barn is a unit of area. Originally used in nuclear physics for expressing the cross sectional area of nuclei and nuclear reactions, today it is used in all fields of high energy physics to express the cross sections of any scattering process, and is best understood as a measure of the...
, and is relatively undiluted by other isotopes of the same element, it is being studied for disposal by nuclear transmutation
Nuclear transmutation
Nuclear transmutation is the conversion of one chemical element or isotope into another. In other words, atoms of one element can be changed into atoms of other element by 'transmutation'...
by re-irradiation with neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...
s or by high-powered lasers.
Groundwater age dating
129I is not deliberately produced for any practical purposes. However, its long half-life and its relative mobility in the environment have made it useful for a variety of dating applications. These include identifying very old waters based on the amount of natural 129I or its 129Xe decay product, as well as identifying younger groundwaters by the increased anthropogenic 129I levels since the 1960s.Meteorite age dating
In 1960 physicist John H. ReynoldsJohn Reynolds (physicist)
John Hamilton Reynolds was an American physicist and a specialist in mass spectrometry.-Life:John H. Reynolds was born in Cambridge, Massachusetts, USA. He studied first at Harvard University and, after serving in the Navy during World War II, at the University of Chicago. There, he was...
discovered that certain meteorite
Meteorite
A meteorite is a natural object originating in outer space that survives impact with the Earth's surface. Meteorites can be big or small. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids...
s contained an isotopic anomaly in the form of an overabundance of 129Xe. He inferred that this must be a decay product
Decay product
In nuclear physics, a decay product is the remaining nuclide left over from radioactive decay. Radioactive decay often involves a sequence of steps...
of long-decayed radioactive iodine-129. This isotope is produced in quantity in nature only in supernova
Supernova
A supernova is a stellar explosion that is more energetic than a nova. It is pronounced with the plural supernovae or supernovas. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months...
explosions. As the half-life of 129I is comparatively short in astronomical terms, this demonstrated that only a short time had passed between the supernova and the time the meteorites had solidified and trapped the 129I. These two events (supernova and solidification of gas cloud) were inferred to have happened during the early history of the Solar System
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
, as the 129I isotope was likely generated before the Solar System was formed, but not long before, and seeded the solar gas cloud isotopes with isotopes from a second source. This supernova source may also have caused collapse of the solar gas cloud.
External links and further reading
- ANL factsheet
- Monitoring iodine-129 in air and milk samples collected near the Hanford Site: an investigation of historical iodine monitoring data
- Studies with natural and anthropogenic iodine isotopes: iodine distribution and cycling in the global environment
- I-129 and Cl-36 in dilute hydrocarbon waters: Marine-cosmogenic,in situ, and anthropogenic sources
- Some Publications using 129I Data from IsoTrace, 1997-2002
- Global distribution of I-129 in rivers and lakes: Implications for iodine cycling in surface reservoirs