Gamma-resonance Mossbauer effect

In nuclear gamma resonance (Mossbauer effect) experiments, the nuclear hyperfine interactions are measured via their influence on the energy of the gamma ray emitted (or absorbed) when the nucleus undergoes a transition between an excited state and its ground state (or between two excited states). Since the nuclear hyperfine energies are small ( 10" -10 eV) compared with... 

Nuclear moment properties of the ground and excited states of selected rare-earth nuclei frequently utilized in nuclear gamma resonance (Mossbauer effect) measurements, adapted from Stevens and Dunlap (1976). Nuclear moment values are given in units of the nuclear magneton... 

The Mossbauer effect, discovered by Rudolf L. Mossbauer in 1957, can in short be described as the recoil-free emission and resonant absorption of gamma radiation by nuclei. In the case of iron, the source consists of Co, which decays with a half-life of 270 days to an excited state of Fe (natural abundance in iron 2%). The latter, in turn, decays rapidly to the first excited state of this isotope. The final decay generates a 14.4 keV photon and a very narrow natural linewidth of the order of nano eV. 

The Mossbauer effect involves the resonance fluorescence of nuclear gamma radiation and can be observed during recoilless emission and absorption of radiation in solids. It can be exploited as a spectroscopic method by observing chemically dependent hyperfine interactions. The recent determination of the nuclear radius term in the isomer shift equation for shows that the isomer shift becomes more positive with increasing s electron density at the nucleus. Detailed studies of the temperature dependence of the recoil-free fraction in and labeled Sn/ show that the characteristic Mossbauer temperatures Om, are different for the two atoms. These results are typical of the kind of chemical information which can be obtained from Mossbauer spectra. 

MOSSBAUER EFFECT. The phenomenon of recoilless resonance lluorescence of gamma rays front nuclei hound itt solids. It was first discovered in 1958 hy R.I.. Mbssbauer. The extreme sharpness of the rccoilless gamma transitions and the relative ease and accuracy in observ ing small energy differences make the effect an important tool in nuclear physics, solid-state physics, mid chemistry. 

Mossbauer effect Resonance absorption of gamma radiation by specific nuclei arranged in a crystal lattice in such a way that the recoil momentum is shared by many atoms. It is the basis of a form of spectroscopy used for studying coordinated metal ions. The principal application in bioinorganic chemistry is 57Fe. The parameters derived from the Mossbauer spectrum (isomer shift, quadrupole splitting, and the hyperfine cou-... 

Although more than 50 nuclei are known for which gamma-ray resonance fluorescence (the Mossbauer effect) has been observed,1 the present contribution will concern itself primarily with data pertinent to experiments using the 14.4 keV radiation of s7Fe and the 23.8 keV radiation of ll9Sn, since the vast majority of studies related to chemical structure problems have exploited these two nuclides. 

The MOssbauer effect is the resonant absorption of y-rays. Gamma emission occurs when a nucleus drops from an excited state to one of lower energy. If these now fall on a nucleus of the same iso-... 

Several features of the Mossbauer effect (resonante absorption of recoil-free gamma radiation) which arise from electron-nucleus interactions are directly connected with the electronic sttucture of the molecule where the resonant nucleus is located. 

Reference [7] provides the detailed analysis of the peculiarities of excited nucleus spontaneous gamma decay both for various types of environment (screen and the system of excited nucleus atom electrons) and accounting for the multimode structure and phase characteristics of the quantized electromagnetic field. It was shown for the first time that the form, distance, and spectral characteristics of the screen most essentially influence the nuclei decay rate. It was also shown that the spontaneous decay character is considerably influenced by the degree of correlation and synchronization of the modes of electromagnetic field surrounding the excited nucleus. Such effect is possible only for the system of resonant Mossbauer nuclei. 

Ihe Mossbauer effect Is based on the resonant absorption of nuclear gamma radiations certain stable nuclear Isotopes. Discovered by Rudolph Mossbauer in 1957, the i enmnenmi spawned a technique which has since had numerous applications in biophysics. With the exception of T e, which is about 2.2% in abundance in the natural isotopic mixtvire of iron, none of the other Mossbauer isotopes occur in high proportion in biomolecules. However, some of these isotopes may be introduced into biological macromolecules by the so called enrichment methods. Mossbauer isotopes most often used for biological applications are T e, and I. It is not possible to present a complete analysis of this phenomenon in this section a brief explanation and a brief idea about the applications of this technique is given below. 

The first example of the recoil-free resonant absorption of gamma rays was observed by Mossbauer using Ir (Mossbauer, 1958) and the Mossbauer effect has now been detected in over one hundred isotopes. However, most of the practical applications of the effect in the technique known as Mossbauer spectroscopy have been with a much smaller number of isotopes in which the conditions for observing the Mossbauer effect and obtaining useful information from it are particularly favourable. 

As briefly outlined in Chapter 1, the Mossbauer effect concerns the resonant absorption of a gamma ray, of frequency coq and wavevector k, by a nucleus. If the absorbing nucleus is located at the position r, the electromagnetic field of the gamma ray at the nucleus can be represented by... 

Abstract This chapter describes a general introduction of the Mossbauer spectroscopy. What is the Mossbauer effect and what is the characteristic feature of the Mossbauer spectroscopy These questions are answered briefly in this chapter. Mossbauer spectroscopy is based on recoilless emission and resonant absorption of gamma radiation by atomic nuclei. Since the electric and magnetic hyperfine interactions of Mossbauer probe atom in solids can be described from the Mossbauer spectra, the essence of experiments, the hyperfine interactions and the spectral line shape are discussed. In addition, the experiments and the new resonance technique with synchrotron radiation have been also briefly described. 

The methods of nuclear magnetic resonance (NMR) and of Mossbauer effect or nuclear gamma resonance (NGR) spectroscopy furnish a broad basis for the study of the structural, electronic, and magnetic properties of rare-earth metals, alloys, and compounds. Taken together, there is hardly a rare-earth or non rare-earth nucleus whose hyperfine interactions cannot be measured. In many cases, results can be cross-checked with measurements on several isotopes of the same element. 

Relaxation effects in Mossbauer spectroscopy are of a different nature from those in NMR. The term relaxation effects or relaxation spectra in nuclear gamma resonance spectroscopy refers to averaging effects that occur in the hyperfine spectrum when the hyperfine interactions fluctuate at a rate more rapid than the nuclear frequency characteristic of the hyperfine interaction itself. This situation is a consequence of the rapid relaxation of the host ion among its energy levels, and the relaxation time for such effects is characteristic of the ion and not of the nuclear spins. The relaxation processes involved also affect electron spin resonance spectra, and their discussion is best considered in that context (see sections 3.3. and 3.4.). In the following subsections the principal interactions which contribute to the nuclear spin relaxation times in NMR experiments are briefly considered, and the connections between these and the parameters characterizing the steady-state spectrum are outlined. 

The Mossbauer effect, also known as the recoilless nucleus resonance absorption of gamma rays, was first discovered and explained by Rudolf L. Mossbauer in 1957, while he was working on his doctoral thesis at Heidelberg. In the following years, more thorough understanding concerning principles, methods, and applications has been achieved by a myriad of research. 

Resonance gamma spectrometry or Mossbauer spectrometry can be used to study the hyperfine interactions between a nucleus and its chemical neighborhood [142], In order to examine these interactions with the help of a Mossbauer spectrometer, the first-order Doppler effect shift of the wave emitted by a moving source is applied. The arrangement used for a Mossbauer spectrometer consists of a radioactive source containing a Mossbauer isotope in an excited state (see Figure 4.54)... 

R. L. Mossbauer (Munich) resonance absorption of gamma radiation and discovery of the effect which bears his name. 

In fact the value is the effective lifetime for Mossbauer component of controlled radiative gamma decay for gamma radiation in solid angle blocked by the resonant screen. 

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