Iron-55 (⁵⁵Fe) is a

radioactive isotope A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess nuclear energy, making it unstable. This excess energy can be used in one of three ways: emitted from the nucleus as gamma radiation; transferr ...

iron Iron () is a chemical element with symbol Fe (from la, ferrum) 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, right in f ...

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 Nucle ...

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 that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ...

and 29

neutrons The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons behave ...

. 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. Thi ...

manganese-55 Naturally occurring manganese (25Mn) is composed of one stable isotope, 55Mn. 25 radioisotopes have been characterized, with the most stable being 53Mn with a half-life of 3.7 million years, 54Mn with a half-life of 312.3 days, and 52Mn with a hal ...

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

X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...

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

X-ray diffraction X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...

. Iron-55 is also a source for

Auger electron The Auger effect or Auger−Meitner effect is a physical phenomenon in which the filling of an inner-shell vacancy of an atom is accompanied by the emission of an electron from the same atom. When a core electron is removed, leaving a vacancy, an ...

s, which are produced during the decay.

Decay

Iron-55 decays via

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 Characteristic X-rays are emitted when outer- shell electrons fill a vacancy in the inner shell of an atom, releasing X-rays in a pattern that is "characteristic" to each element. Characteristic X-rays were discovered by Charles Glover Barkla in 190 ...

-1

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

-2

s with energy of 5.88765 keV and a probability of about 8.2%, or

K-beta Characteristic X-rays are emitted when outer-electron shell, shell electrons fill a vacancy in the inner shell of an atom, releasing X-rays in a pattern that is "characteristic" to each element. Characteristic X-rays were discovered by Charles Glove ...

s 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

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 non-destructive analytical techniques which reveal information about the crystal structure, chemical composition, and physical properties of materials and thin films. These techniques are based on observ ...

. 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 , owners = , headquarters = Paris, Île-de-France, France , coordinates = , spaceport = Guiana Space Centre , seal = File:ESA emblem seal.png , seal_size = 130px , image = Views in the Main Control Room (1205 ...

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 detectors for

gas chromatography Gas chromatography (GC) is a common type of chromatography used in analytical chemistry for separating and analyzing compounds that can be vaporized without decomposition. Typical uses of GC include testing the purity of a particular substance, ...

. The more widely used

nickel-63 Naturally occurring nickel (28Ni) is composed of five stable isotopes; , , , and , with being the most abundant (68.077% natural abundance). 26 radioisotopes have been characterised with the most stable being with a half-life of 76,000 years, ...

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 Naturally occurring iron (26Fe) consists of four stable isotopes: 5.845% of 54Fe (possibly radioactive with a half-life over years), 91.754% of 56Fe, 2.119% of 57Fe and 0.286% of 58Fe. There are 24 known radioactive isotopes, the most stable of w ...

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. N ...

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 (from Greek βίος ''bíos'' "life" and σφαῖρα ''sphaira'' "sphere"), also known as the ecosphere (from Greek οἶκος ''oîkos'' "environment" and σφαῖρα), is the worldwide sum of all ecosystems. It can also be ...

. People close to the test ranges, for example

Iñupiat The Iñupiat (or Inupiat, Iñupiaq or Inupiaq;) 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 border. Their current ...

(

Alaska Natives Alaska Natives (also known as Alaskan Natives, Native Alaskans, Indigenous Alaskans, Aboriginal Alaskans or First Alaskans) are the indigenous peoples of Alaska and include Iñupiat, Yupik, Aleut, Eyak, Tlingit, Haida, Tsimshian, and a numbe ...

) and inhabitants of the

Marshall Islands The Marshall Islands ( mh, Ṃajeḷ), officially the Republic of the Marshall Islands ( mh, Aolepān Aorōkin Ṃajeḷ),'' () is an independent island country and microstate near the Equator in the Pacific Ocean, slightly west of the Internati ...

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

half-life Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ato ...

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