Mössbauer diffraction and interference studies of polycrystalline metals and alloys

After a review of previous work on Mössbauer diffraction and interference phenomena, the principles of the kinematical theory of Mössbauer diffraction are presented. The emphasis is on how the spectroscopic capabilities of the Mössbauer effect can be used to advantage in diffraction studies on materials and condensed matter. Experimental results from Mössbauer powder diffractometry experiments are presented. These results identify the difficulties of Mössbauer powder diffraction experiments, but also demonstrate that a unique chemical environment selectivity is possible for Mössbauer diffraction. Future experiments with Mössbauer powder diffraction require the development of efficient detectors, and some possibilities are suggested.     

Space-time analysis of the Mössbauer radiation scattering

Microscopic theory of the Mössbauer effect is formulated. Nuclei interactions with local magnetic fields and lattice vibrations are taken into account. The analysis is based on the precisely solvable quantum mechanical model of Mössbauer scattering. The process of Mössbauer photon emission and its subsequent scattering on one and two nuclei are analyzed in detail. It is shown that some phenomenological concepts proposed for explanation of fine experiments with 109 Ag nuclei do not obtain microscopic justification.     

Mössbauer Spectroscopy of Locally Inhomogeneous Systems

The paper considers ways for obtaining information from Mössbauer spectra of locally inhomogeneous systems. The entire notion locally inhomogeneous system (LIS) is given a more precise definition applied to Mössbauer spectroscopy. There are considered factors that lead to local inhomogeneity of hyperfine interactions and its mechanisms. Application of LIS Mössbauer spectra processing and analysis methods are discussed. Ways for comprehensive utilization of various methods are described along with the role of a priori information at all processing stages.     

Ion implantation

The extreme sensitivity of Mössbauer Spectroscopy to the local atomic and electronic configuration around ion implanted Mössbauer probes is demonstrated in a number of recent defect configuration studies in semiconductors and metals. A surge of interest is observed towards Mössbauer studies on high dose implantations connected with materials research: recent studies are reviewed dealing with ion beam synthesis, ion beam modification and ion beam mixing of materials.     

Advances in Mössbauer data analysis

The whole Mössbauer community generates a huge amount of data in several fields of human knowledge since the first publication of Rudolf Mössbauer. Interlaboratory measurements of the same substance may result in minor differences in the Mössbauer Parameters (MP) of isomer shift, quadrupole splitting and internal magnetic field. Therefore, a conventional data bank of published MP will be of limited help in identification of substances. Data bank search for exact information became incapable to differentiate the values of Mössbauer parameters within the experimental errors (e.g., IS = 0.22 mm/s from IS = 0.23 mm/s), but physically both values may be considered the same. An artificial neural network (ANN) is able to identify a substance and its crystalline structure from measured MP, and its slight variations do not represent an obstacle for the ANN identification. A barrier to the popularization of Mössbauer spectroscopy as an analytical technique is the absence of a full automated equipment, since the analysis of a Mössbauer spectrum normally is time‐consuming and requires a specialist. In this work, the fitting process of a Mössbauer spectrum was completely automated through the use of genetic algorithms and fuzzy logic. Both software and hardware systems were implemented turning out to be a fully automated Mössbauer data analysis system. The developed system will be presented.     

Mössbauer spectroscopy of disordered magnetic systems

In the given summarizing article, we present the most important aspects of the technique of studying disordered magnetic systems by the Mössbauer effect being developed by us for the broad circle of researchers in magnetism and Mössbauer spectroscopy. The potentialities of this technique in investigating local magnetic characteristics and spin structures of disordered magnetics are assessed by the interpretation of Mössbauer spectroscopy data of various classes of well-studied magnetics (Fe?Al, Fe-V). In the concluding part, we present original results of Mössbauer investigations of binary (Fe?Cr, Fe?Pd and Fe?Au) and quasi-binary (Fe?Pd?Au) alloys characterized by non-trivial macroscopic magnetic properties and complex magnetic phase diagrams.     

Transient Mössbauer spectroscopy with57Fe

Transient Mössbauer experiments with⁵⁷Fe are described. A time resolution of 0.7 ns is achieved with a BaF₂ scintillator. Polar polyvinylidene fluoride film is shown to be well suited for producing fast mechanical modulation. Pulses of recoilless gamma radiation, of width ≈30 ns and heigth 3.5 times the Mössbauer absorption, are generated with stepwise source motion. The efficiency of transient methods in extracting Mössbauer data is demonstrated with sinusoidal motion.     

Determination of retained austenite in bearing steel

M?ssbauer effect experiments in scattering geometry were performed for gauging plates and bearings in order to measure the retained austenite content. The results, obtained from numerical calculations of Mössbauer spectra are compared with the X-ray diffraction measurements. A simple three point Mössbauer effect technique is applied in order to decrease the time of measurements in the industrial use.     

The effect of decaying atomic states on integral and time differential Mössbauer spectra

Mössbauer spectra for time dependent monopole interaction have been calculated for the case that the nuclear transition feeding the Mössbauer state excites an electronic state of the atom. This is assumed to decay in a time comparable with the lifetime of the Mössbauer state. Spectra have been calculated for both time differential and integral experiments.     

Mössbauer spectroscopy under acoustical excitation: thick target effects

A new model of Mössbauer absorption (transmission) spectra with an adequate analysis of the possible effects of acoustic excitation in the thick targets is proposed. In particular, the dependence of the line width of acoustical satellites on the degree of phase correlation of the sound oscillations of resonant nuclei in the target is established by calculations and confirmed in experiment. Such a model is stimulated by an increase in the informativeness of the Mössbauer experiments, using thick samples in ultrasound (US) field, and by possible applications of this research technique. The test measurements of Mössbauer absorption spectra on stainless steel are carried out. The fitting of these spectra confirms the relevance of modifications of the model base of Mössbauer processes in US field.     

Mössbauer Spectroscopy in Archaeology: Introduction and Experimental Considerations

An introduction to the Mössbauer method with emphasis on archaeological applications is given and the merits of scattering and transmission experiments in archaeometric work are discussed. A brief outline of the development of Mössbauer spectroscopy in archaeometry is presented and, finally, some of the rarer applications of the method to problems of archaeological nature are described.     

Artificial neural networks in Mössbauer material science

Mössbauer spectroscopy is a useful technique for characterizing the valencies, electronic and magnetic states, coordination symmetries and site occupancies of the cation. The Mössbauer parameters of isomer shift and quadrupole splitting are useful to distinguish paramagnetic ferrous and ferric iron in several substances, while the internal magnetic field provides information on the crystallinity. In recent years artificial neural networks have shown to be a powerful technique to solve problems of pattern recognition of a mineral from its Mössbauer spectrum, Mössbauer parameters data bank, crystalline structure and magnetic phases of soil from Mössbauer parameters. A computer software named Mössbauer Effect Assistant has been developed. It uses learning vector quantization neural network linked to a Mössbauer data bank that contains Mössbauer parameters of isomer shift, quadrupole spliting, internal magnetic field and the references of the substances. The program identifies the substance under study and/or its crystalline structure when fed with experimental Mössbauer parameters. It can also list the references from the literature by feeding the name of the substance or the author of the publication. Typical application of Mössbauer Effect Assistant in iron-bearing materials Mössbauer spectroscopy is present in user friendly Microsoft Windows environment.     

Gravitational redshift experiments with the high-resolution Mössbauer resonance in67Zn

A gravitational tedshift (GRS) experiment using the high-resolution Mössbauer resonance in⁶⁷Zn is described. The tiny Doppler motion of the source can be checked by a dc-SQUID based displacement sensor. The results on the GRS strongly indicate that solid-state effects, which are difficult to control experimentally, finally limit the accuracy that Mössbauer measurements can provide in determining the GRS. We argue that for this reason conventional Mössbauer experiments most probably will not be able to compete with other methods in future GRS measurements of very high precision.     

Mössbauer investigation of magnetite nanoparticles incorporated in a mesoporous polymeric template

Mössbauer spectroscopy was used in this study to investigate magnetite-based nanocomposites, using mesoporous styrene-divinylbenzene (Sty-DVB) microspheres as the hosting template. The magnetite content was increased in the polymeric template by performing several in situ chemical reactions (one to six cycles) in the hosting material. We found the Mössbauer linewidth associated to site-A increasing with the relative increase of iron in site-A. The Mössbauer linewidth associated to site-B decreases with the relative decrease of iron in site-B. We explain our findings by assuming local change in the homogeneity associated to changes in the relative iron population in sites A and B.     

High-performance Mössbauer spectroscopy: Criteria,possibilities, limitations

Increasing attention is being paid to non-conventional Mössbauer methods in view of the extension of Mössbauer Spectroscopy (MS) to a broadening field of applications. With such long-lasting experiments the shortening of the measuring time required for a given statistical significance is of major practical importance. It is shown that the statistical utility rateu allows one to determine which experimental parameters have a primary role, and it also enables sucessive optimization. It is pointed out for various MS measurements that the strategy for improving the experimental performance is strongly dependent on the given problem. As examples, time-differential Mössbauer measurements and conversion electron Mössbauer spectroscopy are discussed.     

The orientational dependence of paramagnetic mössbauer spectra on a weak magnetic field

Mössbauer experiments were performed on a single crystal of metmyoglobin at 4.2 K. A. small magnetic field was applied in different orientations. The results show the sensitivity of the Mössbauer spectra to the direction of the field. It was possible to detect the heme normal with respect to the orientation of the myoglobin crystal.     

The Mössbauer community in the USA

Scientists in the United States assumed major roles in developing the Mössbauer community during its early years. However, since the termination of the Mössbauer Effect Methodology meetings in 1976, there has been little in the way of regular Mössbauer meetings in the United States. Nevertheless, there is an active United States Mössbauer community, as noted by the number of annual publications – 156 in 2004. In recent decades, attendance of Mössbauer researchers from the United States at the International Conferences on the Applications of the Mössbauer Effect (ICAME) has been far below what would be expected from the number of contributions in the Mössbauer literature. Attempts have been made, unsuccessfully, to arrange for regular Mössbauer meetings. Models for possible future Mössbauer meetings of US scientists are discussed, including a regular biannual meeting, and another being a virtual Mössbauer conference. Also discussed are other models to maintaining an active Mössbauer community in the United States, making use of information technologies that are available to us along with other resources we can use.     

Mössbauer spectroscopy on the surface of Mars. Why?

A Mössbauer spectrometer is included in the preliminary payload of a rover to be placed on the surface of Mars in the Soviet mission to the planct in 1996/1,2/. In counection with the American planctary program it has also been suggested to construct a Mössbauer spectrometer to be landed on Mars /3, 4/. The objective is to study the iron compounds of the Martian soil and rocks by backscattering Mössbauer spectroscopy. The paper describes the significance of the element iron in the study of the evolution of the planetary system and what we might expect to learn from Mössbauer spectroscopy of the surface materials of Mars. The study of Mars is expected to expand substantially in the coming decades, probably culminating with a manned flight to the planet. The international Mössbauer community may contribute significantly to the preparation of these events.     

Precise determination of hyperfine interactions and second-order doppler shift in <Superscript>149</Superscript>Sm Mössbauer transition

We have succeeded in precisely determining the hyperfine interactions, particularly the isomer shifts, in the ¹⁴⁹Sm Mössbauer transition. The difference in the nuclear radii between the ground and excited states is critical for the determination of isomer shifts but is relatively small in ¹⁴⁹Sm. Therefore, the precise determination by ¹⁴⁹Sm Mössbauer spectroscopy is difficult. The recent development of synchrotron-radiation-based Mössbauer spectroscopy allows the isomer shifts to be determined more precisely than previously with the help of wellcollimated synchrotron radiation. In particular, the time-window effect assists the precise determination of hyperfine interactions in the ¹⁴⁹Sm Mössbauer transition because this effect enables us to measure spectra with higher energy resolution than natural linewidth determined by the lifetime of the excited states. Meanwhile, highenergy-resolution measurements to determine center shifts by SR-based Mössbauer spectroscopy enable us to observe the second-order Doppler shift, which has not been discussed, particularly for heavy Mössbauer nuclei. We have discussed the precise determination of isomer shifts and the observation of the second-order Doppler shift using ¹⁴⁹Sm synchrotron-radiation-based Mössbauer spectroscopy.