Iron-55 (⁵⁵Fe) is a

radioactive isotope A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess numbers of either neutrons or protons, giving it excess nuclear energy, and making it unstable. This excess energy can be used in one of three ...

iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...

with a

nucleus Nucleus (: nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucleu ...

containing 26

protons A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' ( elementary charge). Its mass is slightly less than the mass of a neutron and approximately times the mass of an electron (the pro ...

and 29

neutrons The neutron is a subatomic particle, symbol or , that has no electric charge, and a mass slightly greater than that of a proton. The neutron was discovered by James Chadwick in 1932, leading to the discovery of nuclear fission in 1938, the f ...

. It decays by

electron capture Electron capture (K-electron capture, also K-capture, or L-electron capture, L-capture) is a process in which the proton-rich nucleus of an electrically neutral atom absorbs an inner atomic electron, usually from the K or L electron shells. Th ...

to manganese-55 and this process has a half-life of 2.737 years. The emitted

X-ray An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...

s can be used as an X-ray source for various scientific analysis methods, such as

X-ray diffraction X-ray diffraction is a generic term for phenomena associated with changes in the direction of X-ray beams due to interactions with the electrons around atoms. It occurs due to elastic scattering, when there is no change in the energy of the waves. ...

. Iron-55 is also a source for

Auger electron The Auger effect (; ) or Meitner-Auger effect is a physical phenomenon in which atoms eject electrons. It occurs when an inner-shell vacancy in an atom is filled by an electron, releasing energy that causes the emission of another electron from a ...

s, which are produced during the decay.

Decay

Iron-55 decays via

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 filled by an electron from a higher shell. The difference in energy is released by emitting

s of 5.19 keV, with a probability of about 60%,

K-alpha The Siegbahn notation is used in X-ray spectroscopy to name the spectral lines that are characteristic to elements. It was introduced by Manne Siegbahn. The characteristic lines in X-ray emission spectra correspond to atomic electronic transition ...

-1

s with energy of 5.89875 keV and a probability about 16.2%,

-2 X-rays with energy of 5.88765 keV and a probability of about 8.2%, or K-beta X-rays with nominal energy of 6.49045 keV and a probability about 2.85%. The energies of the K-alpha-1 and -2 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 techniques X-ray scattering techniques are a family of analytical techniques which reveal information about the crystal structure, chemical composition, and physical properties of materials and thin films. These techniques are based on observing the scatte ...

. 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 (XRF) is the emission of characteristic "secondary" (or fluorescent) X-rays from a material that has been excited by being bombarded with high-energy X-rays or gamma rays. The phenomenon is widely used for elemental analysis ...

instruments. The

ExoMars ExoMars (Exobiology on Mars) is an astrobiology programme of the European Space Agency (ESA). The goals of ExoMars are to search for signs of past life on Mars, investigate how the Martian water and geochemical environment varies, investigate ...

mission of ESA used, in 2016, such an iron-55 source for its combined

spectrometer. The 2011 Mars mission MSL used a functionally similar spectrometer, but with a traditional, electrically powered X-ray source. The Auger electrons can be applied in

electron capture detector An electron capture detector (ECD) 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 James Lovelock and is used in gas chromatography to ...

s for

gas chromatography Gas chromatography (GC) is a common type of chromatography used in analytical chemistry for Separation process, separating and analyzing compounds that can be vaporized without Chemical decomposition, decomposition. Typical uses of GC include t ...

. The more widely used nickel-63 sources provide electrons from beta decay.

Occurrence

Iron-55 is most effectively produced by irradiation of iron with

. The reaction (⁵⁴Fe(n,γ)⁵⁵Fe and ⁵⁶Fe(n,2n)⁵⁵Fe) of the two most abundant isotopes iron-54 and

iron-56 Iron-56 (56Fe) is the most common isotope of iron. About 91.754% of all iron is iron-56. Of all nuclides, 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 in 1963, considerable amounts of iron-55 have been released into the

biosphere The biosphere (), also called the ecosphere (), is the worldwide sum of all ecosystems. It can also be termed the zone of life on the Earth. The biosphere (which is technically a spherical shell) is virtually a closed system with regard to mat ...

. People close to the test ranges, for example

Iñupiat The Inupiat (singular: Iñupiaq), also known as Alaskan Inuit, are a group of Alaska Natives whose traditional territory roughly spans northeast from Norton Sound on the Bering Sea to the northernmost part of the Canada–United States borde ...

(

Alaska Natives Alaska Natives (also known as Native Alaskans, Alaskan Indians, or Indigenous Alaskans) are the Indigenous peoples of Alaska that encompass a diverse arena of cultural and linguistic groups, including the Iñupiat, Yupik, Aleut, Eyak, Tli ...

) and inhabitants of the

Marshall Islands The Marshall Islands, officially the Republic of the Marshall Islands, is an island country west of the International Date Line and north of the equator in the Micronesia region of the Northwestern Pacific Ocean. The territory consists of 29 c ...

, accumulated significant amounts of radioactive iron. However, the short

half-life Half-life is a mathematical and scientific description of exponential or gradual decay. Half-life, half life or halflife may also refer to: Film * Half-Life (film), ''Half-Life'' (film), a 2008 independent film by Jennifer Phang * ''Half Life: ...

and the test ban decreased, within several years, the available amount of iron-55 nearly to the pre-nuclear test levels.

References

{{Reflist, 2

Decay

Use

Occurrence

References

See also