Strontium-90 (90Sr) is a radioactive
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...
of
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...
, with a half life of 28.8 years. Natural strontium is nonradioactive and nontoxic, but
90Sr is a radioactivity hazard.
90Sr undergoes
β− decayIn nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted. In the case of electron emission, it is referred to as beta minus , while in the case of a positron emission as beta plus...
with
decay energyThe decay energy is the energy released by a radioactive decay. Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting ionizing particles and radiation...
of 0.546
MeVIn physics, the electron volt is a unit of energy. By definition, it is equal to the amount of kinetic energy gained by a single unbound electron when it accelerates through an electrostatic potential difference of one volt...
to an
electronAn electron is a subatomic particle that carries a negative electric charge. It has no known substructure and is believed to be a point particle. An electron has a mass that is approximately 1836 times less than that of the proton. The intrinsic angular momentum of the electron is a half integer...
and the
yttriumYttrium is a chemical element with symbol Y and atomic number 39. It is a silvery-metallic transition metal chemically similar to the lanthanoids and has historically been classified as a rare earth element. Yttrium is almost always found combined with the lanthanoids in rare earth minerals and is...
isotope
90Y, which in turn undergoes
β− decayIn nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted. In the case of electron emission, it is referred to as beta minus , while in the case of a positron emission as beta plus...
with half life of 64 hours and decay energy 2.28 MeV for beta particles to an electron and
90ZrZirconium 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...
(zirconium), which is stable.
Radioactivity
Strontium-90 (90Sr) is a radioactive
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...
of
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...
, with a half life of 28.8 years. Natural strontium is nonradioactive and nontoxic, but
90Sr is a radioactivity hazard.
90Sr undergoes
β− decayIn nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted. In the case of electron emission, it is referred to as beta minus , while in the case of a positron emission as beta plus...
with
decay energyThe decay energy is the energy released by a radioactive decay. Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting ionizing particles and radiation...
of 0.546
MeVIn physics, the electron volt is a unit of energy. By definition, it is equal to the amount of kinetic energy gained by a single unbound electron when it accelerates through an electrostatic potential difference of one volt...
to an
electronAn electron is a subatomic particle that carries a negative electric charge. It has no known substructure and is believed to be a point particle. An electron has a mass that is approximately 1836 times less than that of the proton. The intrinsic angular momentum of the electron is a half integer...
and the
yttriumYttrium is a chemical element with symbol Y and atomic number 39. It is a silvery-metallic transition metal chemically similar to the lanthanoids and has historically been classified as a rare earth element. Yttrium is almost always found combined with the lanthanoids in rare earth minerals and is...
isotope
90Y, which in turn undergoes
β− decayIn nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted. In the case of electron emission, it is referred to as beta minus , while in the case of a positron emission as beta plus...
with half life of 64 hours and decay energy 2.28 MeV for beta particles to an electron and
90ZrZirconium 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...
(zirconium), which is stable. Note that
90Sr/Y is almost a perfectly pure
betaBeta 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...
source; the gamma photon emission from the decay of
90Y is so weak that it can normally be ignored.
Applications
90Sr finds extensive use in medicine and industry, as a radioactive source for thickness gauges and for superficial radiotherapy of some cancers. Controlled amounts of
90Sr and
89Sr can be used in treatment of bone cancer. As the radioactive decay of strontium-90 generates significant amount of heat, and is cheaper than the alternative
238PuPlutonium-238, is a radioactive isotope of plutonium with a half-life of 87.7 years. Because it is a very powerful alpha emitter, this isotope is used for radioisotope thermoelectric generators and radioisotope heater units. One gram of plutonium-238 generates approximately 0.5 watts of...
, it is used as a heat source in many Russian/Soviet
radioisotope thermoelectric generatorA radioisotope thermoelectric generator is an electrical generator which obtains its power from radioactive decay. In such a device, the heat released by the decay of a suitable radioactive material is converted into electricity by the Seebeck effect using an array of thermocouples.RTGs can be...
s, usually in the form of
strontium fluorideStrontium fluoride, SrF2, also called strontium difluoride and strontium fluoride, is a fluoride of strontium...
. It is also used as a
radioactive tracerA radioactive tracer, also called a radioactive label, is a substance containing a radioisotope. Tracers can be used to measure the speed of chemical processes and to track the movement of a substance through a natural system such as a cell or a tissue...
in medicine and agriculture.
Fission product
90Sr is a product of
nuclear fissionIn 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 lighter nuclei, which may eventually produce photons...
. It is present in significant amount in
spent nuclear fuelSpent nuclear fuel, occasionally called used nuclear fuel, is nuclear fuel that has been irradiated in a nuclear reactor to the point where it is no longer useful in sustaining a nuclear reaction....
and in
radioactive wasteRadioactive waste is a waste product containing radioactive material. It is usually the product of a nuclear process such as nuclear fission. However, industries not directly connected to the nuclear industry may produce quantities of radioactive waste. The majority of radioactive waste is...
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...
s and in
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 nuclear tests.
For thermal neutron fission as in today's nuclear power plants, the
fission product yieldNuclear fission splits a heavy nucleus such as uranium or plutonium into two lighter nuclei, which are called fission products. Yield refers to the fraction of a fission product produced per fission.Yield can be broken down by:#Individual isotope...
from
U-235U235 or U-235 may be:* German submarine U-235, a German U-boat of World War II* Uranium-235, an isotope of uraniumbang bang there goes the ship...
is 5.8%, from U-233 6.8%, but from Pu-239 only 2.1%.
Biochemistry
Together with caesium isotopes
134CsCaesium 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...
,
137CsCaesium-137 is a radioactive isotope of caesium which is formed mainly as a fission product by nuclear fission. It has a half-life of 30.17 years, and decays by beta decay to a metastable nuclear isomer of barium-137 . Barium-137m has a half-life of 2.55 minutes and is responsible for all of the...
, and iodine isotope
131IIodine-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....
it was among the most important isotopes regarding health impacts after the
Chernobyl disasterThe Chernobyl disaster was a nuclear reactor accident that occurred on 26 April 1986 at the Chernobyl Nuclear Power Plant in Ukraine . It is considered to be the worst nuclear power plant disaster in history and the only level 7 event on the International Nuclear Event Scale...
.
Strontium-90 is a "
bone seekerBone seeker describes a radioisotope that tends to accumulate in the bones of humans and animals when it is introduced into the body. An example is 90Sr, which behaves chemically like calcium and can replace the calcium in bones....
" that exhibits biochemical behavior similar to
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...
, the next lighter Group 2 element. After entering the organism, most often by ingestion with contaminated food or water, about 70-80% of the dose gets excreted. Virtually all remaining strontium-90 is deposited in
boneBones are rigid organs that form part of the endoskeleton of vertebrates. They function to move, support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...
s and
bone marrowBone marrow is the flexible tissue found in the hollow interior of bones. In adults, marrow in large bones produces new blood cells. It constitutes 4% of total body weight, i.e...
, with the remaining 1% remaining in blood and soft tissues. Its presence in bones can cause bone cancer, cancer of nearby tissues, and
leukemiaLeukemia is a cancer of the blood or bone marrow and is characterized by an abnormal proliferation of blood cells, usually white blood cells . Leukemia is a broad term covering a spectrum of diseases...
. Exposition to
90Sr can be tested by a
bioassayBioassay , or biological standardisation is a type of scientific experiment. Bioassays are essential in the development of new drugs, and in monitoring environmental pollutants....
, most commonly by
urinalysisA urinalysis is an array of tests performed on urine and one of the most common methods of medical diagnosis. A part of a urinalysis can be performed by using urine dipsticks, in which the test results can be read as color changes....
.
Dispersal hazards
Accidental mixing of radioactive sources containing strontium with metal scrap can result in production of radioactive steel. Discarded radioisotope thermoelectric generators are a major source of
90Sr contamination in the area of the former Soviet Union.
External links