Mossbauer spectroscopy recoil energy

In summary, a high-spin state results from dispersion or 3d electrons to all orbitals and a low-spin state is due to 3d electrons being restricted to low-energy orbitals. The microstates of electron configuration can be determined by electron spin resonance and by Mossbauer spectroscopy (recoil-free y-ray resonance absorption), procedures that provide additional information about the redox state of the metal center, spin configuration, symmetry of the ligand field, and type of ligand [2]. 

The recoilless nuclear resonance absorption of y-radiation (Mossbauer effect) has been verified for more than 40 elements, but only some 15 of them are suitable for practical applications [33, 34]. The limiting factors are the lifetime and the energy of the nuclear excited state involved in the Mossbauer transition. The lifetime determines the spectral line width, which should not exceed the hyperfine interaction energies to be observed. The transition energy of the y-quanta determines the recoil energy and thus the resonance effect [34]. 57Fe is by far the most suited and thus the most widely studied Mossbauer-active nuclide, and 57Fe Mossbauer spectroscopy has become a standard technique for the characterisation of SCO compounds of iron. 

Mossbauer spectroscopy is based on transition between energy levels of nuclei with different values of the nuclear spin quantum number /. When a nucleus emits a y-ray, the energy of the emitted radiation is lowered by the recoil of the nucleus. Conversely, the energy needed for absorption is higher than that needed for transition, because the absorbing nucleus absorbs energy in the recoil process. For nuclei tightly bound in solids, however, the effective mass of the emitter and... 

Mossbauer spectroscopy, also called recoil-free nuclear resonance absorption, depends upon resonant absorption of y-rays emitted by a radioactive source by atomic nuclei.120 The phenomenon was initially difficult to observe, but the German physicist Mossbauer devised a way in which to record the absorption of a quantum of energy equal to the difference in two energy states of the atomic nucleus. The method depends upon a Doppler effect observed when the sample or source moves. Consequently, Mossbauer spectra, such as that in Fig. 16-18, are plots of absorp-... 

Zinc is one of the few elements with an isotope usefiil for Mossbauer spectroscopy. Zn has a long-lived isomer state, which leads to potentially narrow line widths (as narrow as 3.2 x 10 nuns ) in the Mossbauer spectrum. Disadvantages are a smaller cross section than, for example, Fe and a much higher recoil energy, decreasing the rate of recoil-free events. The Zn isomer may be produced using a Ga source. 

The fact that atoms in crystalline solids do not suffer a recoil at low energies (<100keV) of emitted or incident particles is made use of in Mossbauer spectroscopy (recoilless y-ray resonance absorption section 10.2). 

Mossbauer spectroscopy is based on the observation that nuclei held rigidly in a lattice can undergo recoil-free emission and absorption of X-radiation the separation of nuclear energy levels can be measured with great accuracy, and it is possible to detect weak interactions between a nucleus and its electronic environment. This may reveal the chemical state of the atom or ion, but only a few nuclei are susceptible to the effect, most work having been done with iron ( Fe) and tin Sn) and a little with ruthenium... 

Mossbauer spectroscopy is specialized, but it can be invaluable when it is available. The technique relies on the recoil-free emission and resonant absorption of y-rays by nuclei that are bound in the solid state. (If it is not in a solid, the free nucleus recoils and no resonance is detected.) To see this resonance, we have to match the energy of the y-ray emitter to the energy of the absorber (the sample), which means that only a small number of elements can be studied. Two that can be studied are tin and iron. The technique gives information on the bonding and coordination, and on the valence (oxidation) state. Since the technique relies on Z, it works for particular isotopes, Fe for iron with Co as the radioactive source of y-rays. (Natural Fe contains -2.19 wt% Fe.)... 

The Mossbauer effect is the emission and resonant absorption of nuclear y-rays studied under conditions such that the nuclei have negligible recoil velocities when y-rays are emitted or absorbed. This is only achieved by working with solid samples in which the nuclei are held rigidly in a crystal lattice. The energy, and thus the frequency of the y-radiation involved, corresponds to the transition between the ground state and the short-lived excited state of the nuclide concerned. Table 4.4 lists properties of several nuclei which can be observed using Mossbauer spectroscopy. 

The discovery of the resonant absorption of gamma-rays in lr by Rudolf Mossbauer in 1958 was a milestone in nuclear physics because it was formerly assumed that such a phenomenon could never occur due to the large recoil energies involved. The interest for this new finding was nevertheless still limited in the first years, but, a real breakthrough emerged from the fact that many isotopes showed a larger and much more sensitive effect. So, a new technique, called Mossbauer spectroscopy, was bom. The most important feature of this spectroscopic method is the extreme sharpness of the emission line which can easily be... 

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