Environmental radioactivity is the study of radioactive materials in the
humanHumans are bipedal primates belonging to the species Homo sapiens in Hominidae, the great ape family. They are the only surviving member of the genus Homo. Humans have a highly developed brain, capable of abstract reasoning, language, introspection, and problem solving...
environmentAn ecosystem is a system of interdependent organisms which share the same habitat, in an area functioning together with all of the physical factors of the environment. Ecosystems can be permanent or temporary. Ecosystems usually form a number of food webs...
. While some radioisotopes are only found on
EarthEarth is the third planet from the Sun. It is the fifth largest of the eight planets in the solar system, and the largest of the terrestrial planets in the Solar System in terms of diameter, mass and density...
as a result of human activity, such as
Strontium-90-Radioactivity:Strontium-90 is a radioactive isotope of strontium, with a half life of 28.8 years. Natural strontium is nonradioactive and nontoxic, but 90Sr is a radioactivity hazard...
(
90Sr) and
Technetium-99Technetium-99 is an isotope of technetium which decays with a half-life of 211,000 years, emitting soft beta rays but no gamma rays, and has a fission product yield of 6.0507% for thermal neutron fission of uranium-235...
(
99Tc), and some isotopes like Potassium-40 (
40K) are only present due to natural processes, a few isotopes are present as a result of both natural processes and human activities e.g.
tritiumTritium is a radioactive isotope of hydrogen. The nucleus of tritium contains one proton and two neutrons, whereas the nucleus of protium contains one proton and no neutrons...
(
3H). The concentration and location of some natural isotopes, particularly
Uranium-238Uranium-238 is the most common isotope of uranium found in nature. When hit by a neutron, it eventually becomes plutonium-239 ....
(
238U), can be affected by human activity.
Background level in soils
Radioactivity is present everywhere (and has been since the formation of the earth). According to the IAEA, one kilogram of soil typically contains the following amounts of the following four natural radioisotopes 370 Bq
40K (typical range 100-700 Bq), 25 Bq
226Ra (typical range 10-50 Bq), 25 Bq
238U (typical range 10-50 Bq) and 25 Bq
232Th (typical range 7-50 Bq). These values are average values and some soils may vary greatly from these norms.
Sea and river silt
A recent report on the Sava river in
SerbiaSerbia , officially the Republic of Serbia , is a country located in both Central and Southeastern Europe. Its territory covers the southern part of the Pannonian Plain and central part of the Balkans...
suggests that many of the river silts contain about 100 Bq kg
−1 of natural radioisotopes (
226Ra,
232Th and
238U). Also according to the
United NationsThe United Nations is an international organization whose stated aims are facilitating cooperation in international law, international security, economic development, social progress, human rights, and the achieving of world peace...
the normal concentration of uranium in soil is 300 μg kg
−1 to 11.7 mg kg
−1.. It is well known that some plants are able to absorb and concentrate metals within their tissues (see
hyperaccumulators- Hyperaccumulators table – 1 :Cs-137 activity was much smaller in leaves of larch and sycamore maple than of spruce: spruce > larch > sycamore maple....
for further detail) and it is known that
iodineIodine , is a chemical element that has the symbol I and atomic number 53. Naturally-occurring iodine is a single isotope with 74 neutrons....
was first isolated from
seaweedSeaweedSeaweed has antioxidents. Is a loose colloquial term encompassing macroscopic, multicellular, benthic marine algae. The term includes some members of the red, brown and green algae...
in
FranceFrance , officially the French Republic , is a country located in Western Europe, with several overseas islands and territories located on other continents. Metropolitan France extends from the Mediterranean Sea to the English Channel and the North Sea, and from the Rhine to the Atlantic Ocean...
which suggests that seaweed is an iodine hyperaccumulator.
For instance Busby quotes
Garland et al. 1989 who reported the plutonium activity in Welsh inter tidal sediments which suggests that the closer a site is to Sellafield the higher the concentration of plutonium in the silt is. Some relationship can be seen but the scatter of points is large (R² = 0.3683) if the data is fitted to an exponential line.
Man-made
The additional radioactivity in the biosphere caused by human activity due to the releases of man-made radioactivity and of Naturally Occurring Radioactive Materials (NORM) can be divided into several classes.
- Normal licensed releases which occur during the regular operation of a plant or process handling man-made radioactive materials.
- For instance the release of 99Tc from a nuclear medicine
Nuclear medicine is a branch or specialty of medicine and medical imaging that uses radioactive isotopes and relies on the process of radioactive decay in the diagnosis and treatment of disease. In nuclear medicine procedures, radionuclides are combined with other chemical compounds or...
department of a hospital which occurs when a person given a Tc imaging agent expels the agent.
- Releases of man-made radioactive materials which occur during an industrial or research accident.
- For instance the Chernobyl accident.
- Releases which occur as a result of military activity.
- For example a nuclear weapons test.
- Releases which occur as a result of a crime
Crime is the breach of one or more rules or laws for which some governing authority, via mechanisms such as police power, may ultimately prescribe a conviction...
.
- For example the Goiânia accident
The Goiânia accident was an incident of radioactive contamination in central Brazil that killed 4, injured 28, and produced over 200 cases of detectable radiation poisoning. On 13 September 1987, an old radiation source was scavenged from an abandoned hospital in Goiânia, the capital of the...
where thieves, unaware of its radioactive content, stole some medical equipment and as a result a number of people were exposed to radiation.
- Releases of naturally occurring radioactive materials (NORM) as a result of mining etc.
- For example the release of the trace quantities of uranium and thorium in coal, when it is burned in power stations.
Farming and the transfer to humans of deposited radioactivity
Just because a radioisotope lands on the surface of the soil, does not mean it will enter the
humanHumans are bipedal primates belonging to the species Homo sapiens in Hominidae, the great ape family. They are the only surviving member of the genus Homo. Humans have a highly developed brain, capable of abstract reasoning, language, introspection, and problem solving...
food chain. After release into the environment radioactive materials can reach humans in a range of different routes, and the chemistry of the element usually dictates the most likely route.
Cows
Jiří Hála's textbook (Radioactivity, Ionizing Radiation and Nuclear Energy, ISBN 807302053X explains how
cattleCattle are the most common type of large domesticated ungulates. They are a prominent modern member of the subfamily Bovinae, are the most widespread species of the genus Bos, and are most commonly classified collectively as Bos primigenius...
only pass a minority of the
strontiumStrontium is a chemical element with the symbol Sr and the atomic number 38. An alkaline earth metal, strontium is a soft silver-white or yellowish metallic element that is highly reactive chemically. The metal turns yellow when exposed to air. It occurs naturally in the minerals celestine and...
,
caesiumCaesium or cesium is the chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-gold alkali metal with a melting point of , which makes it one of only five metals that are liquid at or near room temperature...
,
plutoniumPlutonium is a rare transuranic radioactive element. It is an actinide metal of silvery-white appearance that tarnishes when exposed to air, forming a dull coating when oxidized. The element normally exhibits six allotropes and four oxidation states. It reacts with carbon, halogens, nitrogen and...
and
americiumAmericium is a synthetic element that has the symbol Am and atomic number 95. A radioactive metallic element, americium is an actinide that was obtained in 1944 by Glenn T. Seaborg who was bombarding plutonium with neutrons and was the fourth transuranic element to be discovered. It was named for...
they ingest to the humans who consume
milkMilk is an opaque white liquid produced by the mammary glands of mammals. It provides the primary source of nutrition for young mammals before they are able to digest other types of food. The early lactation milk is known as colostrum, and carries the mother's antibodies to the baby. It can reduce...
and
meatMeat is animal flesh that is used as food. Most often, this means the skeletal muscle and associated fat, but it may also describe other edible tissues such as organs, livers, skin, brains, bone marrow, kidneys, or lungs...
. For instance, for milk if the cow has a daily intake of 1000 Bq of the following isotopes then the milk will have the following activities.
- 90Sr, 2 Bq dm−3
- 137Cs, 5 Bq dm−3
- 239Pu, 0.001 Bq dm−3
- 241Am, 0.001 Bq dm−3
Soil
Jiří Hála's
textbookA textbook is a manual of instruction or a standard book in any branch of study. They are produced according to the demand of educational institutions...
states that soils vary greatly in their ability to bind radioisotopes, the
clayClay is a naturally occurring material composed primarily of fine-grained minerals, which show plasticity through a variable range of water content, and which can be hardened when dried and/or fired...
particles and
humic acidHumic acid is one of the major components of humic substances which are dark brown and major constituents of soil organic matter humus that contributes to soil chemical and physical quality and are also precursors of some fossil fuels...
s can alter the distribution of the isotopes between the soil water and the soil. The distribution coefficient K
d is the ratio of the soil's radioactivity (Bq g
−1) to that of the soil water (Bq ml
−1). If the radioactivity is tightly bonded to by the minerals in the soil then less radioactivity can be absorbed by crops and
grassGrasses, or more technically graminoids, are monocotyledonous, usually herbaceous plants with narrow leaves growing from the base. They include the "true grasses", of the Poaceae family, as well as the sedges and the rushes . The true grasses include cereals, bamboo and the grasses of lawns...
growing in the soil.
- Cs-137 Kd = 1000
- Pu-239
Plutonium is a rare transuranic radioactive element. It is an actinide metal of silvery-white appearance that tarnishes when exposed to air, forming a dull coating when oxidized. The element normally exhibits six allotropes and four oxidation states. It reacts with carbon, halogens, nitrogen and...
Kd = 10000 to 100000
- Sr-90
Strontium is a chemical element with the symbol Sr and the atomic number 38. An alkaline earth metal, strontium is a soft silver-white or yellowish metallic element that is highly reactive chemically. The metal turns yellow when exposed to air. It occurs naturally in the minerals celestine and...
Kd = 80 to 150
- I-131
Iodine , is a chemical element that has the symbol I and atomic number 53. Naturally-occurring iodine is a single isotope with 74 neutrons....
Kd = 0.007 to 50
The trinity test
One dramatic source of man-made radioactivity is a nuclear weapons test. The glassy
trinititeTrinitite, also known as Atomite or Alamogordo Glass, is the name given to the glassy residue left on the desert floor after the plutonium-based Trinity nuclear bomb test on July 16, 1945, near Alamogordo, New Mexico...
formed by the first atom bomb contains radioisotopes formed by neutron activation and nuclear fission. In addition some natural radioisotopes are present. A recent paper (P.P. Parekh, T.M. Semkow, M.A. Torres, D.K. Haines, J.M. Cooper, P.M. Rosenberg and M.E. Kitto,
Jorunal of Environmental Radioactivity, 2006,
85, 103-120) reports the levels of long lived radioisotopes in the trinitite. The trinitite was formed from
feldsparFeldspars are a group of rock-forming tectosilicate minerals which make up as much as 60% of the Earth's crust....
and
quartzQuartz is the second most abundant mineral in the Earth's continental crust . It is made up of a continuous framework of SiO
4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO
2.There are many different varieties of...
which were melted by the heat. Two samples of trinitite were used, the first (left hand side bars) was taken from between 40 and 65 meters of ground zero while the other sample was taken from further away from the
ground zeroThe term ground zero may be used to describe the point on the earth's surface where an explosion occurs...
point.
The
152Eu and
154Eu was mainly formed by the neutron activation of the
europiumEuropium is a chemical element with the symbol Eu and atomic number 63. It was named after the continent of Europe.-Physical:Europium is about as hard as lead and quite ductile...
in the soil, it is clear that the level of radioactivity for these isotopes is highest where the neutron dose to the
soilSoil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics. It is composed of particles of broken rock that have been altered by chemical and...
was larger. Some of the
60Co is generated by activation of the
cobaltCobalt is a hard, lustrous, gray metal, a chemical element with symbol Co and atomic number 27. Although cobalt-based colors and pigments have been used since ancient times for making jewelry and paints, and miners have long used the name kobold ore for some minerals, the free metallic cobalt was...
in the soil, but some was also generated by the activation of the cobalt in the
steelSteel is an alloy consisting mostly of iron, with a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most cost-effective alloying material for iron, but various other alloying elements are used such as manganese, chromium, vanadium, and tungsten...
(100 foot) tower. This
60Co from the tower would have been scattered over the site reducing the difference in the soil levels.
The
133Ba and
241Am are due to the neutron activation of barium and plutonium inside the bomb. The
bariumBarium is a chemical element. It has the symbol Ba, atomic number 56, and is the fifth element in Group 2. Barium is a soft silvery metallic alkaline earth metal. It is never found in nature in its pure form due to its reactivity with air. Its oxide is historically known as baryta but it reacts...
was present in the form of the nitrate in the chemical explosives used while the plutonium was the
fissileIn nuclear engineering, a fissile material is one that is capable of sustaining a chain reaction of nuclear fission.All known fissile materials are capable of sustaining a chain reaction in which either thermal or slow neutrons or fast neutrons predominate...
fuel used.
The
137Cs level is higher in the sample which was further away from the ground zero point– this is thought to be because the precursors to the
137Cs (
137I and
137Xe) and the caesium to a lesser degree are volatile. The natural radioisotopes in the glass are about the same in both locations.
Activation products
The action of neutrons on stable
isotopeIsotopes are different types of atoms of the same chemical element, each having a different number of neutrons. Correspondingly, isotopes differ in mass number but not in atomic number. The difference in the number of nucleons comes from a difference how many neutrons are in the atomic nucleus...
s can form radioisotopes, for instance the neutron bombardment (
neutron activationNeutron activation is the process in which neutron radiation induces radioactivity in materials, and occurs when atomic nuclei capture free neutrons, becoming heavier and entering excited states. The excited nucleus often decays immediately by emitting particles such as neutrons, protons, or alpha...
) of
nitrogenNitrogen is a chemical element that has the symbol N and atomic number 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless and mostly inert diatomic gas at standard conditions, constituting 78% by volume of Earth's atmosphere.Many industrially important...
-14 forms
carbonCarbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
-14. This radioisotope can be released from the
nuclear fuel cycleThe nuclear fuel cycle, also called nuclear fuel chain, is the progression of nuclear fuel through a series of differing stages. It consists of steps in the front end, which are the preparation of the fuel, steps in the service period in which the fuel is used during reactor operation, and steps in...
, this is the radioisotope responsible for the majority of the dose experienced by the population as a result of the activities of the
nuclear powerNuclear power is power produced from controlled nuclear reactions. Commercial plants in use to date use nuclear fission reactions....
industry. For a discussion of the physics of neutron activation see
Neutron activation analysisNeutron Activation Analysis is a nuclear process used for determining certain concentrations of elements in a vast amount of materials. NAA allows discrete sampling of elements as it disregards the chemical form of a sample, and focuses solely on its nucleus...
.
Nuclear bomb tests have increased the specific activity of carbon, whereas the use of fossil fuels has decreased it. See the page on
Radiocarbon datingRadiocarbon dating, or carbon dating, is a radiometric dating method that uses the naturally occurring radioisotope carbon-14 to determine the age of carbonaceous materials up to about 60,000 years. Raw, i.e. uncalibrated, radiocarbon ages are usually reported in radiocarbon years "Before Present"...
for further details.
Fission products
See fission productNuclear fission products are the atomic fragments left after a large atomic nucleus fissions. Typically, a large nucleus like that of uranium fissions by splitting into two smaller nuclei, along with a few neutrons and a large release of energy in the form of heat , gamma rays and neutrinos...
s for more detail, two sources of these radioisotopes is
nuclear falloutFallout is the residual radiation hazard from a nuclear explosion, aptly named because it "falls out" of the atmosphere into which it is spread during the explosion. It commonly refers to the radioactive dust created when a nuclear weapon explodes. This radioactive dust, consisting of hot...
from atomic bombs and nuclear accidents such as
chernobylChornobyl , orChernobyl , is a city in northern Ukraine, in Kiev Oblast , near the border with Belarus. It is twinned with Larne, in Ireland....
. For a good paper about the isotropic signature of the local bomb fallout from a ground burst see T. Imanaka, S. Fukutani, M. Yamamoto, A. Sakaguchi and M. Hoshi,
J. Radiation Research, 2006,
47, Suppl A121-A127.
Discharges from plants within the
nuclear fuel cycleThe nuclear fuel cycle, also called nuclear fuel chain, is the progression of nuclear fuel through a series of differing stages. It consists of steps in the front end, which are the preparation of the fuel, steps in the service period in which the fuel is used during reactor operation, and steps in...
introduce fission products to the environment, the releases from
nuclear reprocessingNuclear reprocessing separates components of spent nuclear fuel.Reprocessing serves multiple purposes, whose relative importance has changed over time:*Producing plutonium for nuclear weapons...
plants tend to be medium to long-lived radioisotopes, this is because the
nuclear fuelNuclear fuel is any material that can be consumed to derive nuclear energy, by analogy to chemical fuel that is burned to derive energy. By far the most common type of nuclear fuel is heavy fissile elements that can be made to undergo nuclear fission chain reactions in a nuclear fission reactor;...
is allowed to cool for several years before being dissolved in the
nitric acidNitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosive and toxic strong acid.Colorless when pure older samples tend to acquire a stronger yellow cast due to the accumulation of oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as...
. The releases from
nuclear reactorA nuclear reactor is a device in which nuclear chain reactions are initiated, controlled, and sustained at a steady rate.The most significant use of nuclear reactors is as an energy source for the generation of electrical power and for the power in some ships...
accidents and bomb detonations will contain a greater amount of the short-lived radioisotopes (when the amounts are expressed in activity
BqBQ may refer to:* Aeromar Lineas Aereas Dominicanas: IATA airline designator* Birds Queensland, the ornithological society of Queensland, Australia* Bloc Québécois, a political party of Canada* Broadcast quality...
)).
Short lived
An example of a short-lived fission product is
Iodine-131Iodine-131 , also called radioiodine, is a radioisotope of iodine which has medical and pharmaceutical uses. It is also a radioactive hazard and was a significant contributor to the health effects of the Chernobyl disaster....
, this can also be formed as an activation product by the
neutronThe neutron is a subatomic particle with no net electric charge and a mass slightly larger than that of a proton.Neutron are usually found in atomic nuclei. The nuclei of most atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of protons in a...
activation of
telluriumTellurium is a chemical element that has the symbol Te and atomic number 52. A brittle silver-white metalloid which looks similar to tin, tellurium is chemically related to selenium and sulfur. Tellurium is primarily used in alloys and as a semiconductor.-Characteristics:Tellurium is extremely...
.
In both bomb fallout and a release from a power reactor accident, the short-lived isotopes cause the dose rate on day one to be much higher than that which will be experienced at the same site many days later. This holds true even if no attempts at decontamination are made. In the graphs below, the total gamma dose rate and the share of the dose due to each main isotope released by the Chernobyl accident are shown.
Medium lived
The classic example is
137Cs, the
caesiumCaesium or cesium is the chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-gold alkali metal with a melting point of , which makes it one of only five metals that are liquid at or near room temperature...
is released in bomb fallout and from the
nuclear fuel cycleThe nuclear fuel cycle, also called nuclear fuel chain, is the progression of nuclear fuel through a series of differing stages. It consists of steps in the front end, which are the preparation of the fuel, steps in the service period in which the fuel is used during reactor operation, and steps in...
. A paper has been written on the radioactivity found in
oysterThe word oyster is used as a common name for a number of distinct groups of bivalve molluscs which live in marine or brackish habitats. The valves are highly calcified....
s found in the
Irish SeaThe Irish Sea also known as the Mann Sea or Manx Sea, separates the islands of Ireland and Britain. It is connected to the Atlantic Ocean in the south by St George's Channel, and in the north by the North Channel...
, these were found by
gamma spectroscopyGamma spectroscopy involves the spectroscopy of radionuclides. While a Geiger counter determines only the count rate, a gamma spectrometer also determines the energy of gamma rays emitted by radioactive substances....
to contain
141Ce,
144Ce,
103Ru,
106Ru,
137Cs,
95Zr and
95Nb. In addition a
zincZinc , also known as spelter, is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
activation product (
65Zn) was found, this is thought to be due to the
corrosionCorrosion is the disintegration of a material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means a loss of electrons of metals reacting with water and oxygen. Weakening of iron due to oxidation of the iron atoms is a...
of
magnoxMagnox is a now obsolete type of nuclear power reactor which was designed and is still in use in the United Kingdom, and was exported to other countries, both as a power plant, and, when operated accordingly, as a producer of plutonium for nuclear weapons...
fuel cladding in cooling ponds. It is likely that the modern releases of all these isotopes from Windscale is smaller.
An important part of the
ChernobylChornobyl , orChernobyl , is a city in northern Ukraine, in Kiev Oblast , near the border with Belarus. It is twinned with Larne, in Ireland....
release was the caesium-137, this isotope is responsible for much of the long term (at least one year after the fire) external exposure which has occurred at the site. Also the caesium isotopes in the fallout have had an effect on farming.
A good source of data on the subject of
caesiumCaesium or cesium is the chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-gold alkali metal with a melting point of , which makes it one of only five metals that are liquid at or near room temperature...
in
ChernobylChornobyl , orChernobyl , is a city in northern Ukraine, in Kiev Oblast , near the border with Belarus. It is twinned with Larne, in Ireland....
fallout exists at
http://www.uiar.org.ua/Eng/index.htm, this is the
Ukrainian Research Institute for Agricultural Radiology.
A great deal of caesium was released during the
Goiânia accidentThe Goiânia accident was an incident of radioactive contamination in central Brazil that killed 4, injured 28, and produced over 200 cases of detectable radiation poisoning. On 13 September 1987, an old radiation source was scavenged from an abandoned hospital in Goiânia, the capital of the...
where a radioactive source (made for medical use) was stolen and then smashed open during an attempt to convert it into scrap metal. The accident could have been stopped at several stages; first, the last legal owners of the source failed to make arrangements for the source to be stored in a safe and secure place; and second, the scrap metal workers who took it did not recognise the markings which indicated that it was a radioactive object.
P. Soudek, Š. Valenová, Z. Vavříková and T. Vaněk,
Journal of Environmental Radioactivity, 2006,
88, 236-250 report details of the uptake of
90Sr and
137Cs into
sunflowerSunflowers are annual plants native to the Americas, that possess a large inflorescence .-Description :...
s grown under hydroponic conditions. The caesium was found in the leaf veins, in the stem and in the
apicalApical, from the Latin apex meaning to be at the apex or tip, may refer to:*Apical consonant, a consonant produced with the tip of the tongue*Apical dendrite, a type of dendrite found on pyramidal neurons*Apical dominance...
leaves. It was found that 12% of the caesium entered the plant, and 20% of the strontium. This paper also reports details of the effect of
potassiumPotassium is the chemical element with the symbol K , atomic number 19, and atomic mass 39.0983. Potassium was first isolated from potash...
,
ammoniumThe ammonium cation is a positively charged polyatomic cation of the chemical formula NH. It has a formula weight of 18.05 and is formed by the protonation of ammonia...
and
calciumCalcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft grey alkaline earth metal, and is the fifth most abundant element by mass in the Earth's crust...
ions on the uptake of the radioisotopes.
Caesium binds tightly to
clayClay is a naturally occurring material composed primarily of fine-grained minerals, which show plasticity through a variable range of water content, and which can be hardened when dried and/or fired...
minerals such as
illiteIllite is a non-expanding, clay-sized, micaceous mineral. Illite is a phyllosilicate or layered alumino-silicate. Its structure is constituted by the repetition of tetrahedron – octahedron – tetrahedron layers. The interlayer space is mainly occupied by poorly hydrated potassium cations...
and
montmorilloniteMontmorillonite is a very soft phyllosilicate group of minerals that typically form in microscopic crystals, forming a clay. It is named after Montmorillon in France. Montmorillonite, a member of the smectite family, is a 2:1 clay, meaning that it has 2 tetrahedral sheets sandwiching a central...
; hence it remains in the upper layers of soil where it can be accessed by plants with shallow roots (such as grass). Hence
grassGrasses, or more technically graminoids, are monocotyledonous, usually herbaceous plants with narrow leaves growing from the base. They include the "true grasses", of the Poaceae family, as well as the sedges and the rushes . The true grasses include cereals, bamboo and the grasses of lawns...
and
mushroomA mushroom is the fleshy, spore-bearing fruiting body of a fungus, typically produced above ground on soil or on its food source. The standard for the name "mushroom" is the cultivated white button mushroom, Agaricus bisporus, hence the word mushroom is most often applied to those fungi that have...
s can carry a considerable amount of
137Cs which can be transferred to humans through the
food chainFood chains describe the eating relationships between species within an ecosystem or a particular living place. Many types of food chains or webs are applicable depending on habitat or environmental factors...
. One of the best countermeasures in dairy farming against
137Cs is to mix up the soil by deeply ploughing the soil. This has the effect of putting the
137Cs out of reach of the shallow
rootIn vascular plants, the root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial or aerating . Furthermore, a stem normally occurring below ground is not exceptional either...
s of the grass, hence the level of radioactivity in the grass will be lowered. Also after a nuclear war or serious accident the removal of top few cm of
soilSoil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics. It is composed of particles of broken rock that have been altered by chemical and...
and its burial in a shallow trench will reduce the long term gamma dose to
humanHumans are bipedal primates belonging to the species Homo sapiens in Hominidae, the great ape family. They are the only surviving member of the genus Homo. Humans have a highly developed brain, capable of abstract reasoning, language, introspection, and problem solving...
s due to
137Cs as the gamma
photonIn physics, a photon is an elementary particle, the quantum of the electromagnetic field and the basic "unit" of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...
s will be attenuated by their passage through the
soilSoil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics. It is composed of particles of broken rock that have been altered by chemical and...
. The more remote the trench is from humans and the deeper the trench is the better the degree of protection which will be afforded to the human population.
In
livestockLivestock are one or more domesticated animals raised in an agricultural setting to produce commodities such as food or fiber, or labor...
farming an important countermeasure against
137Cs is to feed to animals a little
prussian bluePrussian blue is a dark blue pigment – one of the first synthetic pigments – which was synthesized for the first time in Berlin around the year 1706. It was named "Preußisch blau" and "Berlinisch Blau" in 1709 by its first trader...
. This
ironIron is a metallic chemical element with the symbol Fe and atomic number 26. Iron is a group 8 and period 4 element and is therefore classified as a transition metal. Iron and iron alloys are by far the most common metals and the most common ferromagnetic materials in everyday use...
potassiumPotassium is the chemical element with the symbol K , atomic number 19, and atomic mass 39.0983. Potassium was first isolated from potash...
cyanideA cyanide is any chemical compound that contains the cyano group , which consists of a carbon atom triple-bonded to a nitrogen atom. Inorganic cyanides are hydrogen cyanide salts in which cyanide is generally the anion CN
-. Organic compounds that have a -C≡N functional group bonded to...
compound acts as an ion-exchanger. The cyanide is so tightly bonded to the iron that it is safe for a human to eat several grams of prussian blue per day. The prussian blue reduces the biological half life (different from the
nuclear half lifeHalf-life is the period of time, for a substance undergoing decay, to decrease by half. The name originally was used to describe a characteristic of unstable atoms , but may apply to any quantity which follows a set-rate decay....
) of the caesium. The physical or nuclear half life of
137Cs is about 30 years. This is a constant which can not be changed but the biological half life is not a constant. It will change according to the nature and habits of the organism for which it is expressed.
CaesiumCaesium or cesium is the chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-gold alkali metal with a melting point of , which makes it one of only five metals that are liquid at or near room temperature...
in humans normally has a biological half life of between one and four months. An added advantage of the prussian blue is that the caesium which is stripped from the animal in the
droppingsFeces, faeces, or fæces is a waste product from an animal's digestive tract expelled through the anus during defecation.-Etymology:...
is in a form which is not available to plants. Hence it prevents the caesium from being recycled. The form of prussian blue required for the treatment of humans or animals is a special grade. Attempts to use the
pigmentA pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...
grade used in
paintPaint is any liquid, liquifiable, or mastic composition which after application to a substrate in a thin layer is converted to an opaque solid film.-History:...
s have not been successful.
Plutonium and the other actinides
In popular culture plutonium is credited with being the ultimate threat to
life and limb which is wrong; while ingesting plutonium is not likely to be good for one's health, other radioisotopes such as
radiumRadium is a radioactive chemical element which has the symbol Ra and atomic number 88. Its appearance is almost pure white, but it readily oxidizes on exposure to air, turning black. Radium is an alkaline earth metal that is found in trace amounts in uranium ores. It is extremely radioactive...
are more toxic to humans. Regardless, the introduction of the
transuranium elements such as
plutoniumPlutonium is a rare transuranic radioactive element. It is an actinide metal of silvery-white appearance that tarnishes when exposed to air, forming a dull coating when oxidized. The element normally exhibits six allotropes and four oxidation states. It reacts with carbon, halogens, nitrogen and...
into the
environmentThe natural environment, commonly referred to simply as the environment, is a term that encompasses all living and non-living things occurring naturally on Earth or some region thereof....
should be avoided wherever possible. Currently the activities of the
nuclear reprocessingNuclear reprocessing separates components of spent nuclear fuel.Reprocessing serves multiple purposes, whose relative importance has changed over time:*Producing plutonium for nuclear weapons...
industry have been subject to great debate as one of the fears of those opposed to the industry is that large amounts of plutonium will be either mismanaged or released into the environment. In the past one of the biggest releases of plutonium into the environment has been nuclear bomb testing.
- Those tests in the air scattered some plutonium over the entire globe; this great dilution of the plutonium has resulted in the threat to each exposed person being very small as each person is only exposed to a very small amount.
- The underground tests tend to form molten rock which rapidly cools and seals in the actinides so rendering them unable to move, again the threat to humans is small unless the site of the test is dug up.
- The safety trials where bombs were subject to simulated accidents pose the greatest threat to people; some areas of land used for such experiments (conducted in the open air) have not been fully released for general use despite in one case an extensive decontamination.
For further details see actinides in the environmentActinides in the environment refer to the sources, environmental behaviour and effects of actinides in Earth's environment. Environmental radioactivity is not limited solely to actinides; non-actinides such as radon and radium are of note....
.
Activation products from cosmic rays
Cosmogenic isotopes (or
cosmogenic nuclides) are rare
isotopeIsotopes are different types of atoms of the same chemical element, each having a different number of neutrons. Correspondingly, isotopes differ in mass number but not in atomic number. The difference in the number of nucleons comes from a difference how many neutrons are in the atomic nucleus...
s created when a high-energy
cosmic rayCosmic rays are energetic particles originating from outer space that impinge on Earth's atmosphere. Almost 90% of all the incoming cosmic ray particles are protons, almost 10% are helium nuclei , and slightly under 1% are heavier elements and electrons...
interacts with the
nucleusThe nucleus is the very dense region consisting of nucleons at the center of an atom. Almost all of the mass in an atom is made up from the protons and neutrons in the nucleus, with a very small contribution from the orbiting electrons....
of an
in situIn situ is a Latin phrase meaning in the place. It is used in many different contexts.-Aerospace:In the aerospace industry, equipment on board aircraft must be tested in situ, or in place, to confirm everything functions properly as a system. Individually, each piece may work but interference from...
atomThe atom is a basic unit of matter consisting of a dense, central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons...
. These isotopes are produced within earth materials such as
rockIn geology, rock is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...
s or
soilSoil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics. It is composed of particles of broken rock that have been altered by chemical and...
, in
Earth'sEarth is the third planet from the Sun. It is the fifth largest of the eight planets in the solar system, and the largest of the terrestrial planets in the Solar System in terms of diameter, mass and density...
atmosphereThe Earth's atmosphere is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...
, and in extraterrestrial items such as
meteoriteA meteorite is a natural object originating in outer space that survives an impact with the Earth's surface. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids...
s. By measuring cosmogenic isotopes,
scientistA scientist, in the broadest sense, is any person who engages in a systematic activity to acquire knowledge or an individual that engages in such practices and traditions that are linked to schools of thought or philosophy. In a more restricted sense, a scientist is an individual who uses the...
s are able to gain insight into a range of
geologicalGeology is the science and study of the solid and liquid matter that constitutes the Earth. The field of geology encompasses the study of the composition, structure, physical properties, dynamics, and history of Earth materials, and the processes by which they are formed, moved, and changed...
and
astronomicalAstronomy is the scientific study of celestial objects and phenomena that originate outside the Earth's atmosphere...
processes. There are both radioactive and
stableStable isotopes are chemical isotopes that are not radioactive . By this definition, there are 256 known stable isotopes of the 80 elements which have one or more stable isotopes. A list of these is given at the end of this article...
cosmogenic isotopes. Some of these radioisotopes are
tritiumTritium is a radioactive isotope of hydrogen. The nucleus of tritium contains one proton and two neutrons, whereas the nucleus of protium contains one proton and no neutrons...
,
carbonCarbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
-14 and
phosphorusPhosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus is commonly found in inorganic phosphate rocks. Elemental phosphorus exists in two major forms - white phosphorus and red phosphorus...
-32.
Production modes
Here is a list of radioisotopes formed by the action of cosmic rays on the atomosphere, the list also contains the production mode of the isotope.
These data were obtained from the SCOPE50 report, see table 1.9 of chapter 1.
Isotopes formed by the action of cosmic rays on the air
| Isotope | Mode of formation |
|---|
| ³H (tritium) |
14N (n, 12C)³H |
| 7Be |
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 stray electrons to alpha particles....
(N and O) |
| 10Be |
Spallation (N and O) |
| 11C |
Spallation (N and O) |
| 14C |
14N (n, p) 14C |
| 18F |
18O (p, n)18F and Spallation (Ar) |
| 22Na |
Spallation (Ar) |
| 24Na |
Spallation (Ar) |
| 28Mg |
Spallation (Ar) |
| 31Si |
Spallation (Ar) |
| 32Si |
Spallation (Ar) |
| 32P |
Spallation (Ar) |
| 34mCl |
Spallation (Ar) |
| 35S |
Spallation (Ar) |
| 36Cl |
35Cl (n, )36Cl |
| 37Ar |
37Cl (p, n)37Ar |
| 38Cl |
Spallation (Ar) |
| 38 |
Spallation (Ar) |
| 39Ar |
38Ar (n, )39Ar |
| 39Cl |
40Ar (n, np)39Cl & spallation (Ar) |
| 41Ar |
40Ar (n, )41Ar |
| 81Kr |
80Kr (n, ) 81Kr |
Transfer to ground
The level of
berylliumBeryllium is the chemical element with the symbol Be and atomic number 4.A bivalent element, beryllium is found naturally only combined with other elements in minerals. Notable gemstones which contain beryllium include Beryl and Chrysoberyl...
-7 in the air is related to the
sun spotSun SPOT is a wireless sensor network mote developed by Sun Microsystems. The device is built upon the IEEE 802.15.4 standard...
cycle, as radiation from the sun forms this radioisotope in the atmosphere. The rate at which it is transferred from the air to the ground is controlled in part by the weather.
Applications in geology listed by isotope
Commonly measured long lived cosmogenic isotopes
| element A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. The term is also used to refer to a pure chemical substance composed of atoms with the same number of protons.Common examples of elements...
| massThe atomic mass is the mass of an atom, most often expressed in unified atomic mass units. The atomic mass may be considered to be the total mass of protons, neutrons and electrons in a single atom...
| half-life Half-life is the period of time, for a substance undergoing decay, to decrease by half. The name originally was used to describe a characteristic of unstable atoms , but may apply to any quantity which follows a set-rate decay....
(years) | typical application |
|---|
heliumHelium is the chemical element with atomic number 2, and is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert monatomic gas that heads the noble gas group in the periodic table...
|
3 |
- stable - |
exposure dating of olivineThe mineral olivine is a magnesium iron silicate with the formula 2SiO 4...
-bearing rocks |
berylliumBeryllium is the chemical element with the symbol Be and atomic number 4.A bivalent element, beryllium is found naturally only combined with other elements in minerals. Notable gemstones which contain beryllium include Beryl and Chrysoberyl...
|
10 |
1.36 million |
exposure dating of quartzQuartz is the second most abundant mineral in the Earth's continental crust . It is made up of a continuous framework of SiO 4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO 2.There are many different varieties of...
-bearing rocks, sediment, dating of ice cores, measurement of erosion rates |
carbonCarbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
|
14 |
5,730 |
datingRadiocarbon dating, or carbon dating, is a radiometric dating method that uses the naturally occurring radioisotope carbon-14 to determine the age of carbonaceous materials up to about 60,000 years. Raw, i.e. uncalibrated, radiocarbon ages are usually reported in radiocarbon years "Before Present"...
of organic matter, water |
neonNeon is the chemical element that has the symbol Ne and atomic number 10. Although a very common element in the universe, it is rare on Earth. A colorless, inert noble gas under standard conditions, neon gives a distinct reddish-orange glow when used in discharge tubes and neon lamps...
|
21 |
- stable - |
dating of very stable, long-exposed surfaces, including meteorite A meteorite is a natural object originating in outer space that survives an impact with the Earth's surface. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids...
s |
| aluminum |
26 |
720,000 |
exposure dating of rocks, sediment |
chlorineChlorine Chlorine Chlorine ( , from the Greek word 'χλωρóς' (khlôros, meaning 'pale green'), is the chemical element with atomic number 17 and symbol Cl. It is a halogen, found in the periodic table in group 17 (formerly VII, VIIa, or VIIb). As the chloride ion, which is part of common salt and...
|
36 |
308,000 |
exposure dating of rocks, groundwater Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of lithologic formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in...
tracer |
calciumCalcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft grey alkaline earth metal, and is the fifth most abundant element by mass in the Earth's crust...
|
41 |
103,000 |
exposure dating of carbonate rock Carbonate rocks are a class of sedimentary rocks composed primarily of carbonate minerals. The two major types are limestone and dolomite, composed of calcite and the mineral dolomite respectively...
s |
iodineIodine , is a chemical element that has the symbol I and atomic number 53. Naturally-occurring iodine is a single isotope with 74 neutrons....
|
129 |
15.7 million |
groundwater tracer |
Applications of dating
Because cosmogenic isotopes have long half-lives (anywhere from thousands to millions of years), scientists find them useful for geologic
datingRadiometric dating is a technique used to date materials, usually based on a comparison between the observed abundance of a naturally occurring radioactive isotope and its decay products, using known decay rates...
. Cosmogenic isotopes are produced at or near the surface of the Earth, and thus are commonly applied to problems of measuring ages and rates of
geomorphicGeomorphology is the scientific study of landforms and the processes that shape them...
and
sedimentSediment is any particulate matter that can be transported by fluid flow, and which eventually is deposited.Sediments are most often transported by water transported by wind and glaciers...
ary events and processes.
Specific applications of cosmogenic isotopes include:
- exposure dating of earth surfaces, including glacially
A glacier is a perennial mass of ice which moves over land. A glacier forms in locations where the mass accumulation of snow and ice exceeds ablation over many years...
-scoured bedrockIn stratigraphy, bedrock is the native consolidated rock underlying the surface of a terrestrial planet, usually the Earth. Above the bedrock is usually an area of broken and weathered unconsolidated rock in the basal subsoil...
, faultIn geology, a fault or fault line is a planar fracture in rock in which the rock on one side of the fracture has moved with respect to the rock on the other side. Large faults within the Earth's crust are the result of differential or shear motion and active fault zones are the causal locations of...
scarpIn geomorphology, an escarpment is a transition zone between different physiogeographic provinces that involves a sharp, steep elevation differential, characterized by a cliff or steep slope. Usually escarpment is used interchangeably with scarp...
s, landslideA landslide is a geological phenomenon which includes a wide range of ground movement, such as rock falls, deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments...
debris
- burial dating of sediment, bedrock, ice
- measurement of steady-state erosion
Erosion is a gravity driven process that moves solids in the natural environment or their source and deposits them elsewhere...
rates
- absolute dating
Absolute dating is the process of determining a specific date for an archaeological or palaeontological site or artifact. Some archaeologists prefer the terms chronometric or calendar dating, as use of the word "absolute" implies a certainty and precision that is rarely possible in archaeology...
of organic matter (radiocarbon datingRadiocarbon dating, or carbon dating, is a radiometric dating method that uses the naturally occurring radioisotope carbon-14 to determine the age of carbonaceous materials up to about 60,000 years. Raw, i.e. uncalibrated, radiocarbon ages are usually reported in radiocarbon years "Before Present"...
)
- absolute dating of water masses, measurement of groundwater transport rates
- absolute dating of meteorites, lunar surfaces
Methods of measurement for the long lived isotopes
To measure cosmogenic isotopes produced within solid earth materials, such as rock, samples are generally first put through a process of mechanical separation. The sample is crushed and desirable material, such as a particular mineral (
quartzQuartz is the second most abundant mineral in the Earth's continental crust . It is made up of a continuous framework of SiO
4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO
2.There are many different varieties of...
in the case of Be-10), is separated from non-desirable material by using a density separation in a heavy liquid medium such as LST (lithium sodium tungstate).
The sample is then dissolved, a common isotope carrier added (Be-9 carrier in the case of Be-10), and the aqueous solution is purified down to an oxide or other pure solid.
Finally, the ratio of the rare cosmogenic isotope to the common isotope is measured using
acceleratorA particle accelerator is a device that uses electric fields to propel ions or charged subatomic particles to high speeds and to contain them in well-defined beams. An ordinary CRT television set is a simple form of accelerator...
mass spectrometryMass spectrometry is an analytical technique for the determination of the elemental composition of a sample or molecule. It is also used for elucidating the chemical structures of molecules, such as peptides and other chemical compounds...
. The original concentration of cosmogenic isotope in the sample is then calculated using the measured isotopic ratio, the mass of the sample, and the mass of carrier added to the sample.
External links
Radium and Radon from the decay of long lived actinides
RadiumRadium is a radioactive chemical element which has the symbol Ra and atomic number 88. Its appearance is almost pure white, but it readily oxidizes on exposure to air, turning black. Radium is an alkaline earth metal that is found in trace amounts in uranium ores. It is extremely radioactive...
and
radonRadon is a chemical element with symbol Rn and atomic number 86. It is a radioactive, colorless, odorless, tasteless noble gas, occurring naturally as the decay product of radium. It is one of the heaviest substances that remains a gas under normal conditions and is considered to be a health...
are in the environment because they are decay products of
uraniumUranium is a silvery-white metallic chemical element in the actinide series of the periodic table that has the symbol U and atomic number 92. Besides its 92 protons, a uranium nucleus can have between 141 and 146 neutrons. The most common uranium isotopes are U-238 and U-235 . A uranium atom has...
and
thoriumThorium is a chemical element with the symbol Th and atomic number 90. It is a naturally occurring, slightly radioactive metal. Thorium is estimated to be about three to four times more abundant than uranium in the earth's crust...
.
For further details about thorium see actinides in the environmentActinides in the environment refer to the sources, environmental behaviour and effects of actinides in Earth's environment. Environmental radioactivity is not limited solely to actinides; non-actinides such as radon and radium are of note....
, for further details of uranium see uranium in the environmentUranium in the environment refers to the science of the sources, environmental behaviour and effects of actinides in Earth's environment and in animals . This page is a subpage of actinides in the environment.- From the land :...
while for further details about radium and radon please see radium in the environment- Radium in quack medicine :See the story of Eben Byers for details of one very nasty case which involved a product called Radithor which contained 1 mCi of
226Ra and 1 mCi of
228Ra per bottle...
.
The radon (
222Rn) released into the air decays to
210Pb and other radioisotopes, the levels of
210PbLead is a main-group element with symbol Pb and atomic number 82. Lead is a soft, malleable poor metal, also considered to be one of the heavy metals. Lead has a bluish-white color when freshly cut, but tarnishes to a dull grayish color when exposed to air...
can be measured. The rate of deposition of this radioisotope is dependent on the weather. Here is a graph of the deposition rate observed in
Japanis an island country in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, People's Republic of China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
.
Uranium-lead dating
The
uranium-lead radiometric dating scheme is one of the oldest available, as well as one of the most highly respected. It has been refined to the point that the error in dates of rocks about three billion years old is no more than two million years.
UraniumUranium is a silvery-white metallic chemical element in the actinide series of the periodic table that has the symbol U and atomic number 92. Besides its 92 protons, a uranium nucleus can have between 141 and 146 neutrons. The most common uranium isotopes are U-238 and U-235 . A uranium atom has...
-
leadLead is a main-group element with symbol Pb and atomic number 82. Lead is a soft, malleable poor metal, also considered to be one of the heavy metals. Lead has a bluish-white color when freshly cut, but tarnishes to a dull grayish color when exposed to air...
dating is usually performed on the mineral
zirconZircon is a mineral belonging to the group of nesosilicates. Its chemical name is zirconium silicate and its corresponding chemical formula is ZrSiO4. A common empirical formula showing some of the range of substitution in zircon is 1-x4x-y...
(ZrSiO
4), though it can be used on other materials. Zircon incorporates uranium
atomThe atom is a basic unit of matter consisting of a dense, central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons...
s into its crystalline structure as substitutes for
zirconiumZirconium is a chemical element with the symbol Zr and atomic number 40. It is a lustrous, gray-white, strong transition metal that resembles titanium. Zirconium is used as an alloying agent due to its high resistance to corrosion. It is never found as a native metal; it is obtained mainly from...
, but strongly rejects lead. It has a high blocking temperature, is resistant to mechanical weathering and is chemically inert. Zircon also forms multiple crystal layers during metamorphic events, which each may record an isotopic age of the event. These can be dated by a SHRIMP
ionAn ion is an atom or molecule where the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge...
microprobe.
One of its advantages is that any sample provides two clocks, one based on uranium-235's decay to lead-207 with a
half-lifeHalf-life is the period of time, for a substance undergoing decay, to decrease by half. The name originally was used to describe a characteristic of unstable atoms , but may apply to any quantity which follows a set-rate decay....
of about 703 million years, and one based on uranium-238's decay to lead-206 with a half-life of about 4.5 billion years, providing a built-in crosscheck that allows accurate determination of the age of the sample even if some of the lead has been lost.
For further details see
radiometric datingRadiometric dating is a technique used to date materials, usually based on a comparison between the observed abundance of a naturally occurring radioactive isotope and its decay products, using known decay rates...
and
exponential decayA quantity is said to be subject to exponential decay if it decreases at a rate proportional to its value. Symbolically, this can be expressed as the following differential equation, where N is the quantity and λ is a positive number called the decay constant.The solution to this equation is:Here...
.
Further reading
- Radioactivity, Ionizing Radiation and Nuclear Energy, by J. Hala and J.D. Navratil
- A review of the subject has been published by SCOPE
Scope or Scopes may refer to:* SCOPE , a technique of creating gene libraries* Scope , the range in which a variable can be referenced* Scope , a mouthwash brand by Procter & Gamble* SCOPE...
in the report SCOPE 50 Radioecology after chernobyl.