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| | Broadcast Transmitter Operator Jean Ternes from Kamsack, has several hobbies and interests which include house repair, 10 hatha yoga positions and maintain a journal. Will soon carry on a contiki trip which will include going to the Delhi. |
| The '''Mössbauer effect''', or '''recoilless nuclear resonance fluorescence''', is a physical phenomenon discovered by [[Rudolf Mössbauer]] in 1958. It involves the resonant and [[Atomic recoil|recoil]]-free emission and absorption of [[gamma ray|gamma radiation]] by atomic nuclei bound in a solid. Its main application is in [[Mössbauer spectroscopy]].
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| ==History==
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| The emission and absorption of [[x-ray]]s by gases had been observed previously, and it was expected that a similar phenomenon would be found for [[gamma ray]]s, which are created by [[atomic nucleus|nuclear]] transitions (as opposed to x-rays, which are typically produced by [[electron]]ic transitions). However, attempts to observe nuclear resonance produced by gamma-rays in gases failed due to energy being lost to recoil, preventing resonance (the [[Doppler effect]] also broadens the gamma-ray spectrum). Mössbauer was able to observe resonance in nuclei of solid [[iridium]], which raised the question of why gamma-ray resonance was possible in solids, but not in gases. Mössbauer proposed that, for the case of atoms bound into a solid, under certain circumstances a fraction of the nuclear events could occur essentially without recoil. He attributed the observed resonance to this recoil-free fraction of nuclear events.
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| The Mössbauer effect was one of the last major discoveries in physics to be originally reported in German language. The first report in English language was a letter describing a repetition of the experiment.<ref>
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| {{cite journal
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| |last1=Craig |first1=P.
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| |last2=Dash |first2=J.
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| |last3=McGuire |first3=A.
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| |last4=Nagle |first4=D.
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| |last5=Reiswig |first5=R.
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| |year=1959
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| |title=Nuclear Resonance Absorption of Gamma Rays in Ir<sup>191</sup>
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| |journal=[[Physical Review Letters]]
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| |volume=3 |issue=5 |pages=221
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| |bibcode=1959PhRvL...3..221C
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| |doi=10.1103/PhysRevLett.3.221
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| }}</ref>
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| The discovery was rewarded with the [[Nobel Prize in Physics]] in 1961 together with [[Robert Hofstadter]]'s research of [[electron scattering]] in atomic nuclei.
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| ==Description==
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| [[File:Mossbauer 51Fe.png|thumb|right|150px]]
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| The Mössbauer Effect is a process in which a nucleus emits or absorbs gamma rays without loss of energy to a nuclear recoil. It was discovered by the German physicist Rudolf L. Mössbauer in 1958 and has proved to be remarkably useful for basic research in physics and chemistry. It has been used, for instance, in precisely measuring small energy changes in nuclei, atoms, and crystals induced by electrical, magnetic, or gravitational fields. In a transition of a nucleus from a higher to a lower energy state with accompanying emission of gamma rays, the emission generally causes the nucleus to recoil, and this takes energy from the emitted gamma rays. Thus the gamma rays do not have sufficient energy to excite a target nucleus to be examined. However, Mössbauer discovered that is possible to have transitions in which the recoil is absorbed by a whole crystal in which the emitting nucleus is bound. Under these circumstances, the energy that goes into the recoil is a negligible portion of the energy of the transition. Therefore the emitted gamma rays carry virtually all of the energy liberated by the nuclear transition. The gamma rays thus are able to induce a reverse transition, under similar conditions of negligible recoil, in a target nucleus of the same material as the emitter but in a lower energy state. In general, gamma rays are produced by nuclear transitions from an unstable high-energy state, to a stable low-energy state. The energy of the emitted gamma ray corresponds to the energy of the nuclear transition, minus an amount of energy that is lost as recoil to the emitting atom. If the lost "recoil energy" is small compared with the energy [[linewidth]] of the nuclear transition, then the gamma ray energy still corresponds to the energy of the nuclear transition, and the gamma ray can be absorbed by a second atom of the same type as the first. This emission and subsequent absorption is called [[resonance|resonant]] [[fluorescence]]. Additional recoil energy is also lost during absorption, so in order for resonance to occur the recoil energy must actually be less than half the linewidth for the corresponding nuclear transition.
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| The amount of energy in the recoiling body ({{math|''E''<small>{{sub|R}}</small>}}) can be found from momentum conservation:
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| :<math>|P_\mathrm{R}| = |P_\mathrm{\gamma}| \,</math>
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| where {{math|''P''<small>{{sub|R}}</small>}} is the momentum of the recoiling matter, and {{math|''P''{{sub|γ}}}} the momentum of the gamma ray. Substituting energy into the equation gives:
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| :<math>E_\mathrm{R} = \frac{E_\mathrm{\gamma}^2}{2Mc^2}</math>
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| where {{math|''E''<small>{{sub|R}}</small>}} ({{val|0.002|ul=eV}} for {{SimpleNuclide2|Fe|57}}) is the energy lost as recoil, {{math|''E''{{sub|γ}}}} is the energy of the gamma ray ({{val|14.4|ul=keV}} for {{SimpleNuclide2|Fe|57}}), {{math|''M''}} ({{val|56.9354|ul=u}} for {{SimpleNuclide2|Fe|57}}) is the mass of the emitting or absorbing body, and ''c'' is the [[speed of light]].<ref>
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| {{Cite web
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| | last = Nave | first = C.R.
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| | year = 2005
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| | title = Mössbauer Effect in Iron-57
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| | url = http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/mossfe.html
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| | work = [[HyperPhysics]]
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| | publisher = [[Georgia State University]]
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| | accessdate = 7 June 2010
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| }}</ref> In the case of a gas the emitting and absorbing bodies are atoms, so the mass is relatively small, resulting in a large recoil energy, which prevents resonance. (Note that the same equation applies for recoil energy losses in x-rays, but the photon energy is much less, resulting in a lower energy loss, which is why gas-phase resonance could be observed with x-rays.)
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| In a solid, the nuclei are bound to the lattice and do not recoil in the same way as in a gas. The lattice as a whole recoils but the recoil energy is negligible because the {{math|''M''}} in the above equation is the mass of the whole lattice. However, the energy in a decay can be taken up or supplied by lattice vibrations. The energy of these vibrations is quantised in units known as ''phonons''. The Mössbauer effect occurs because there is a finite probability of a decay occurring involving no phonons. Thus in a fraction of the nuclear events (the '''recoil-free fraction''', given by the [[Lamb–Mössbauer factor]]), the entire crystal acts as the recoiling body, and these events are essentially recoil-free. In these cases, since the recoil energy is negligible, the emitted gamma rays have the appropriate energy and resonance can occur.
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| In general (depending on the half-life of the decay), gamma rays have very narrow linewidths. This means they are very sensitive to small changes in the energies of nuclear transitions. In fact, gamma rays can be used as a probe to observe the effects of interactions between a nucleus and its electrons and those of its neighbors. This is the basis for Mössbauer spectroscopy, which combines the Mössbauer effect with the [[Doppler effect]] to monitor such interactions.
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| [[Zero-phonon line and phonon sideband|Zero-phonon optical transitions]], a process closely analogous to the Mössbauer effect, can be observed in lattice-bound [[chromophore]]s at low temperatures.
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| ==See also==
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| * [[Pound–Rebka experiment]]
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| * [[Isomeric shift]]
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| * [[Mössbauer spectroscopy]]
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| ==Further reading==
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| *{{cite journal
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| | last= Mössbauer |first=R. L.
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| | year = 1958
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| | title = Kernresonanzfluoreszenz von Gammastrahlung in Ir<sup>191</sup>
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| | journal = [[Zeitschrift für Physik A]]
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| | volume = 151 | issue =2 | pages = 124–143
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| | language = German
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| | bibcode = 1958ZPhy..151..124M
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| | doi = 10.1007/BF01344210
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| }}
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| *{{cite book
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| | last = Frauenfelder |first=H.
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| | year = 1962
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| | title = The Mössbauer Effect
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| | publisher = [[W. A. Benjamin]]
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| | lccn = 61018181
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| }}
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| *{{cite journal
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| | last = Eyges | first = L.
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| | year = 1965
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| | title = Physics of the Mössbauer Effect
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| | journal = [[American Journal of Physics]]
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| | volume = 33 | issue = 10 | pages = 790–802
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| | bibcode = 1965AmJPh..33..790E
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| | doi = 10.1119/1.1970986
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| }}
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| *{{cite journal
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| | last = Hesse | first = J.
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| | year = 1973
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| | title = Simple Arrangement for Educational Mössbauer-Effect Measurements
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| | journal = [[American Journal of Physics]]
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| | volume = 41 |issue= | pages = 127–129
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| | bibcode = 1973AmJPh..41..127H
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| | doi = 10.1119/1.1987142
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| }}
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| *{{cite journal
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| | last = Ninio | first = F.
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| | year = 1973
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| | title = The Forced Harmonic Oscillator and the Zero-Phonon Transition of the Mössbauer Effect
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| | journal = [[American Journal of Physics]] | |
| | volume = 41 | issue = 5 | pages = 648–649
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| | bibcode = 1973AmJPh..41..648N
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| | doi = 10.1119/1.1987323
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| }}
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| *{{cite journal
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| | last = Vandergrift |first=G.
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| | last2=Fultz |first2=B.
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| | year = 1998
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| | title = The Mössbauer effect explained
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| | journal = [[American Journal of Physics]]
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| | volume = 66 | issue = 7 | pages = 593–596
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| | bibcode = 1998AmJPh..66..593V
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| | doi = 10.1119/1.18911
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| }}
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| * Encyclopedia Americana (1988) "Mossbauer Effect" Encyclopedia Americana 19: 500 ISBN 0-7172-0119-8 (set)
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| ==References==
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| {{reflist}}
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| {{DEFAULTSORT:Mossbauer Effect}}
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| [[Category:Condensed matter physics]]
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| [[Category:Nuclear physics]]
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| [[Category:Physical phenomena]]
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Broadcast Transmitter Operator Jean Ternes from Kamsack, has several hobbies and interests which include house repair, 10 hatha yoga positions and maintain a journal. Will soon carry on a contiki trip which will include going to the Delhi.