Krypton-85
Encyclopedia
Krypton 85 is a radioisotope of krypton
.
It decays into rubidium
-85, with a half-life
of 10.756 years and a maximum decay energy
of 0.687 MeV
.
Its most common decay (99.57%) is by beta particle
emission with maximum energy of 687
keV
and an average energy of 251 keV. The second most common (0.43%) is by beta particle
emission (maximum energy of 173 keV) followed by gamma ray
emission (energy of 514 keV).
Other decay modes have very small probabilities and emit less energetic gammas.
The only other long-lived radioisotope of krypton is krypton-81 with a 210,000 year half-life; others have half-lives of less than two days.
Krypton-85 is produced in small quantities by the interaction of cosmic rays with the stable krypton-84 (which is present in concentrations of about 1 cm3 per cubic meter). However, since the mid-1940s, much larger quantities have been artificially produced as a product of nuclear fission
. When uranium-235
, or another fissile
nucleus fissions, it usually splits into two large fragments (fission product
s) with mass numbers around 90-140, and two or three neutron
s. About three atoms of krypton-85 are produced for every 1000 fissions (i.e. it has a fission yield of 0.3%). This is only about 20% of the total fission product of mass 85, as most decay from a short-lived excited state of 85Kr directly to 85Rb without passing through the longer-lived nuclear isomer
.
About 5 MCi of the isotope was released into the atmosphere as a result of nuclear weapons tests between 1945 and the end of atmospheric testing in 1962. The 1979 accident at the Three Mile Island nuclear power plant
released about 50 kCi of Kr-85 into the atmosphere
and the Chernobyl accident released about 5 MCi.
The atmospheric concentration of krypton-85 peaked in around 1970, when it reached around 10 pCi/m3 (around 0.4 Bq/m3). Since then the cessation of atmospheric weapons tests and the reduced production of plutonium has, because of the short half-life of the isotope, led to a sharp reduction in the atmospheric concentration, according to the Human Health Fact Sheet.
For wide-area atmospheric monitoring, krypton-85 is the best indicator for clandestine plutonium separations.
A large nuclear power plant
produces about 300 kCi of the isotope per year, most or all retained in the spent nuclear fuel
rods. Nuclear reprocessing
currently releases Kr-85 to the atmosphere when the spent fuel is dissolved. It would also be possible to capture and store it as nuclear waste or for use.
. The existence of Kr-85 in discharge tube of the lamps can make the lamps easy to ignite.
The sealed spark gap assemblies contained in ignition excitors used in some older turbine/jet engines contain a very small amount of krypton-85 in order to obtain consistent ionization levels and uniform operation. The amount of radiation from the average gap is approximately the same as that of a radium-dial wrist watch but should be handled carefully.
Krypton-85 was used in cold-cathode voltage regulator electron tubes, such as the type 5651.
Krypton-85 is used to inspect aircraft components for small defects. Krypton-85 is allowed to penetrate small cracks, and then its presence is detected by autoradiography. The method is called "krypton gas penetrant imaging". The gas penetrates smaller openings than the liquids used in dye penetrant inspection
and fluorescent penetrant inspection
.
Krypton-85 is used to test for leaks in semiconductors (MIL-STD-883H) and piping.
Krypton
Krypton is a chemical element with the symbol Kr and atomic number 36. It is a member of Group 18 and Period 4 elements. A colorless, odorless, tasteless noble gas, krypton occurs in trace amounts in the atmosphere, is isolated by fractionally distilling liquified air, and is often used with other...
.
It decays into rubidium
Rubidium
Rubidium is a chemical element with the symbol Rb and atomic number 37. Rubidium is a soft, silvery-white metallic element of the alkali metal group. Its atomic mass is 85.4678. Elemental rubidium is highly reactive, with properties similar to those of other elements in group 1, such as very rapid...
-85, 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 10.756 years and a maximum decay energy
Decay energy
The 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 0.687 MeV
MEV
MeV and meV are multiples and submultiples of the electron volt unit referring to 1,000,000 eV and 0.001 eV, respectively.Mev or MEV may refer to:In entertainment:* Musica Elettronica Viva, an Italian musical group...
.
Its most common decay (99.57%) is by beta particle
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...
emission with maximum energy of 687
keV
Kev
Kev can refer to:*Kev Hawkins, a fictional character.*Kevin, a given name occasionally shortened to "Kev".*Kiloelectronvolt, a unit of energy who symbol is "KeV".* Krefelder Eislauf-VereinKEV can refer to:...
and an average energy of 251 keV. The second most common (0.43%) is by beta particle
emission (maximum energy of 173 keV) followed by gamma ray
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...
emission (energy of 514 keV).
Other decay modes have very small probabilities and emit less energetic gammas.
The only other long-lived radioisotope of krypton is krypton-81 with a 210,000 year half-life; others have half-lives of less than two days.
Krypton-85 is produced in small quantities by the interaction of cosmic rays with the stable krypton-84 (which is present in concentrations of about 1 cm3 per cubic meter). However, since the mid-1940s, much larger quantities have been artificially produced as a product of nuclear fission
Nuclear 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...
. When uranium-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...
, or another fissile
Fissile
In nuclear engineering, a fissile material is one that is capable of sustaining a chain reaction of nuclear fission. By definition, fissile materials can sustain a chain reaction with neutrons of any energy. The predominant neutron energy may be typified by either slow neutrons or fast neutrons...
nucleus fissions, it usually splits into two large fragments (fission product
Fission product
Nuclear 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. The...
s) with mass numbers around 90-140, and two or three 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. About three atoms of krypton-85 are produced for every 1000 fissions (i.e. it has a fission yield of 0.3%). This is only about 20% of the total fission product of mass 85, as most decay from a short-lived excited state of 85Kr directly to 85Rb without passing through the longer-lived nuclear isomer
Nuclear isomer
A nuclear isomer is a metastable state of an atomic nucleus caused by the excitation of one or more of its nucleons . "Metastable" refers to the fact that these excited states have half-lives more than 100 to 1000 times the half-lives of the other possible excited nuclear states...
.
About 5 MCi of the isotope was released into the atmosphere as a result of nuclear weapons tests between 1945 and the end of atmospheric testing in 1962. The 1979 accident at the Three Mile Island nuclear power plant
Three Mile Island accident
The Three Mile Island accident was a core meltdown in Unit 2 of the Three Mile Island Nuclear Generating Station in Dauphin County, Pennsylvania near Harrisburg, United States in 1979....
released about 50 kCi of Kr-85 into the atmosphere
and the Chernobyl accident released about 5 MCi.
The atmospheric concentration of krypton-85 peaked in around 1970, when it reached around 10 pCi/m3 (around 0.4 Bq/m3). Since then the cessation of atmospheric weapons tests and the reduced production of plutonium has, because of the short half-life of the isotope, led to a sharp reduction in the atmospheric concentration, according to the Human Health Fact Sheet.
For wide-area atmospheric monitoring, krypton-85 is the best indicator for clandestine plutonium separations.
A large nuclear power plant
Nuclear power plant
A nuclear power plant is a thermal power station in which the heat source is one or more nuclear reactors. As in a conventional thermal power station the heat is used to generate steam which drives a steam turbine connected to a generator which produces electricity.Nuclear power plants are usually...
produces about 300 kCi of the isotope per year, most or all retained in the 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...
rods. Nuclear reprocessing
Nuclear reprocessing
Nuclear reprocessing technology was developed to chemically separate and recover fissionable plutonium from irradiated nuclear fuel. Reprocessing serves multiple purposes, whose relative importance has changed over time. Originally reprocessing was used solely to extract plutonium for producing...
currently releases Kr-85 to the atmosphere when the spent fuel is dissolved. It would also be possible to capture and store it as nuclear waste or for use.
Uses in Industry
It is used in arc discharge lamps commonly used in the entertainment industry for large HMI film lights as well as High Intensity Discharge lamps for outdoor lightingLighting
Lighting or illumination is the deliberate application of light to achieve some practical or aesthetic effect. Lighting includes the use of both artificial light sources such as lamps and light fixtures, as well as natural illumination by capturing daylight...
. The existence of Kr-85 in discharge tube of the lamps can make the lamps easy to ignite.
The sealed spark gap assemblies contained in ignition excitors used in some older turbine/jet engines contain a very small amount of krypton-85 in order to obtain consistent ionization levels and uniform operation. The amount of radiation from the average gap is approximately the same as that of a radium-dial wrist watch but should be handled carefully.
Krypton-85 was used in cold-cathode voltage regulator electron tubes, such as the type 5651.
Krypton-85 is used to inspect aircraft components for small defects. Krypton-85 is allowed to penetrate small cracks, and then its presence is detected by autoradiography. The method is called "krypton gas penetrant imaging". The gas penetrates smaller openings than the liquids used in dye penetrant inspection
Dye penetrant inspection
Dye penetrant inspection , also called liquid penetrant inspection or penetrant testing , is a widely applied and low-cost inspection method used to locate surface-breaking defects in all non-porous materials...
and fluorescent penetrant inspection
Fluorescent penetrant inspection
Fluorescent Penetrant Inspection is a type of dye penetrant inspection in which a fluorescent dye is applied to the surface of a non-porous material in order to detect defects that may compromise the integrity or quality of the part in question...
.
Krypton-85 is used to test for leaks in semiconductors (MIL-STD-883H) and piping.