Iron-55
Encyclopedia
Iron-55 or 55Fe is a radioactive isotope of iron
with a nucleus
containing 26 protons and 29 neutrons. It decays by electron capture
to manganese-55 and this process has a half-life of 2.737 years. The emitted X-ray
s can be used as an X-ray source for various scientific analysis methods, such as X-ray diffraction. Iron-55 is also a source for Auger electron
s, which are produced during the decay.
to manganese-55 with a half-life of 2.737 years. The electrons around the nucleus rapidly adjust themselves to the lowered charge without leaving their shell, and shortly thereafter the vacancy in the "K" shell left by the nuclear-captured electron is is filled by an electron from a higher shell. The difference in energy is released by emitting Auger electron
s of 5.19 keV, with a probability of about 60%, -alpha]-1] X-ray
s with energy of 5.889 keV and a probability about 16.2 %, -alpha]-2] X-ray
s with energy of 5.888 keV and a probability of about 8.2 %, or K-beta
X-ray
s with nominal energy of 6.49 keV and a probability about 2.85 %. The energies of these X-rays are so similar that they are often specified as mono-energetic radiation with 5.9 keV photon energy. Its probability is about 28 %. The remaining 12 % is accounted for by lower-energy Auger electrons and a few photons from other, minor transitions.
. The advantages of the emitted X-rays are that they are monochromatic and are continuously produced over a years-long period. No electrical power is needed for this emission, which is ideal for portable X-ray instruments, such as X-ray fluorescence
instruments. The ExoMars
mission of ESA is planned to use, in 2018, such an iron-55 source for its combined X-ray diffraction/X-ray fluorescence
spectrometer. The 2011 Mars mission MSL09
will use a functionally similar spectrometer, but with a traditional, electrically powered X-ray source.
The Auger electrons can be applied in electron capture detector
s for gas chromatography. The more widely used nickel-63 sources provide electrons from beta decay.
with neutrons yields iron-55. Most of the observed iron-55 is produced in these irradiation reactions, and it is not a primary fission product.
As a result of atmospheric nuclear tests in the 1950s, and until the test ban
in 1963, considerable amounts of iron-55 have been released into the biosphere
. People close to the test ranges, for example Eskimos and inhabitants of the Marshall Islands
, accumulated significant amounts of radioactive iron. However, the short half-life
and the test ban decreased, within several years, the available amount of iron-55 nearly to the pre-nuclear test levels.
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
with a nucleus
Atomic nucleus
The nucleus is the very dense region consisting of protons and neutrons at the center of an atom. It was discovered in 1911, as a result of Ernest Rutherford's interpretation of the famous 1909 Rutherford experiment performed by Hans Geiger and Ernest Marsden, under the direction of Rutherford. The...
containing 26 protons and 29 neutrons. It decays by electron capture
Electron capture
Electron capture is a process in which a proton-rich nuclide absorbs an inner atomic electron and simultaneously emits a neutrino...
to manganese-55 and this process has a half-life of 2.737 years. The emitted X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
s can be used as an X-ray source for various scientific analysis methods, such as X-ray diffraction. Iron-55 is also a source for Auger electron
Auger electron
The Auger effect is a physical phenomenon in which the transition of an electron in an atom filling in an inner-shell vacancy causes the emission of another electron. When a core electron is removed, leaving a vacancy, an electron from a higher energy level may fall into the vacancy, resulting in...
s, which are produced during the decay.
Decay
Iron-55 decays via electron captureElectron capture
Electron capture is a process in which a proton-rich nuclide absorbs an inner atomic electron and simultaneously emits a neutrino...
to manganese-55 with a half-life of 2.737 years. The electrons around the nucleus rapidly adjust themselves to the lowered charge without leaving their shell, and shortly thereafter the vacancy in the "K" shell left by the nuclear-captured electron is is filled by an electron from a higher shell. The difference in energy is released by emitting Auger electron
Auger electron
The Auger effect is a physical phenomenon in which the transition of an electron in an atom filling in an inner-shell vacancy causes the emission of another electron. When a core electron is removed, leaving a vacancy, an electron from a higher energy level may fall into the vacancy, resulting in...
s of 5.19 keV, with a probability of about 60%, -alpha]-1] X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
s with energy of 5.889 keV and a probability about 16.2 %, -alpha]-2] X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
s with energy of 5.888 keV and a probability of about 8.2 %, or K-beta
K-beta
K-beta emissions, similar to K-alpha emissions, result when an electron transitions to the innermost "K" shell from a 3p orbital of the second or "M" shell ....
X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
s with nominal energy of 6.49 keV and a probability about 2.85 %. The energies of these X-rays are so similar that they are often specified as mono-energetic radiation with 5.9 keV photon energy. Its probability is about 28 %. The remaining 12 % is accounted for by lower-energy Auger electrons and a few photons from other, minor transitions.
Use
The K-alpha X-rays emitted by the manganese-55 after the electron capture have been used as a laboratory source of X-rays in various X-ray scattering techniquesX-ray scattering techniques
X-ray scattering techniques are a family of non-destructive analytical techniques which reveal information about the crystallographic structure, chemical composition, and physical properties of materials and thin films...
. The advantages of the emitted X-rays are that they are monochromatic and are continuously produced over a years-long period. No electrical power is needed for this emission, which is ideal for portable X-ray instruments, such as X-ray fluorescence
X-ray fluorescence
X-ray fluorescence is the emission of characteristic "secondary" X-rays from a material that has been excited by bombarding with high-energy X-rays or gamma rays...
instruments. The ExoMars
ExoMars
ExoMars is a European-led robotic mission to Mars currently under development by the European Space Agency with collaboration by NASA...
mission of ESA is planned to use, in 2018, such an iron-55 source for its combined X-ray diffraction/X-ray fluorescence
X-ray fluorescence
X-ray fluorescence is the emission of characteristic "secondary" X-rays from a material that has been excited by bombarding with high-energy X-rays or gamma rays...
spectrometer. The 2011 Mars mission MSL09
Mars Science Laboratory
The Mars Science Laboratory is a National Aeronautics and Space Administration mission with the aim to land and operate a rover named Curiosity on the surface of Mars. The MSL was launched November 26, 2011, at 10:02 EST and is scheduled to land on Mars at Gale Crater between August 6 and 20, 2012...
will use a functionally similar spectrometer, but with a traditional, electrically powered X-ray source.
The Auger electrons can be applied in electron capture detector
Electron capture detector
An electron capture detector is a device for detecting atoms and molecules in a gas through the attachment of electrons via electron capture ionization. The device was invented in 1957 by Dr. James E...
s for gas chromatography. The more widely used nickel-63 sources provide electrons from beta decay.
Occurrence
Iron-55 is most effectively produced by irradiation of iron with neutrons. The reaction (54Fe(n,γ)55Fe and 56Fe(n,2n)55Fe) of the two most abundant isotopes iron-54 and iron-56Iron-56
Iron-56 is the most common isotope of iron. About 91.754% of all iron is iron-56.Of all isotopes, iron-56 has the lowest mass per nucleon. With 8.8 MeV binding energy per nucleon, iron-56 is one of the most tightly bound nuclei....
with neutrons yields iron-55. Most of the observed iron-55 is produced in these irradiation reactions, and it is not a primary fission product.
As a result of atmospheric nuclear tests in the 1950s, and until the test ban
Partial Test Ban Treaty
The treaty banning nuclear weapon tests in the atmosphere, in outer space and under water, often abbreviated as the Partial Test Ban Treaty , Limited Test Ban Treaty , or Nuclear Test Ban Treaty is a treaty prohibiting all test detonations of nuclear weapons...
in 1963, considerable amounts of iron-55 have been released into the biosphere
Biosphere
The biosphere is the global sum of all ecosystems. It can also be called the zone of life on Earth, a closed and self-regulating system...
. People close to the test ranges, for example Eskimos and inhabitants of the Marshall Islands
Marshall Islands
The Republic of the Marshall Islands , , is a Micronesian nation of atolls and islands in the middle of the Pacific Ocean, just west of the International Date Line and just north of the Equator. As of July 2011 the population was 67,182...
, accumulated significant amounts of radioactive iron. However, the short 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...
and the test ban decreased, within several years, the available amount of iron-55 nearly to the pre-nuclear test levels.