Physical principles of the mossbauer effect for solving inner-nuclear phenomena in solids

In this work, using a number of examples, it is shown that one of the promising methods for studying the physicochemical state of matter is Mossbauer spectroscopy with all the variety of its methodological approaches. The processes occurring in the shell of atoms have a negligible effect on intranuclear phenomena, and often turn out to be inaccessible for detection by other methods. Mossbauer spectroscopy reveals these infl uences. Four methodological approaches have been implemented and an experimental base has been created for observing the resonant absorption of quanta by 57Fe nuclei. Techniques for absorption (MS), Emission Mossbauer Spectroscopy (EMS), Characteristic X-ray Radiation (CXR), Conversion Electron Mossbauer Spectroscopy (CEMS) allow, practically without restrictions on the elemental composition and geometric dimensions of samples (from bulk to nanometer), to carry out studies. Mini Review Physical principles of the mossbauer effect for solving inner-nuclear phenomena in solids AK Shokanov1, MF Vereshchak2, IA Manakova3, YA Smikhan4* and YA Ospanbekov5 1Kazakh National Pedagogical University named after Abay, Almaty, Kazakhstan 2Institute of Nuclear Physics, Almaty, Kazakhstan 3Institute of Nuclear Physics, Almaty, Kazakhstan 4Kazakh National Pedagogical University named after Abay, Almaty, Kazakhstan 5Kazakh National Pedagogical University named after Abay, Almaty, Kazakhstan Received: 30 December, 2020 Accepted: 11 January, 2021 Published: 12 January, 2021 *Corresponding author: Yerkebulan Smikhan, Kazakh National Pedagogical University named after Abay, Almaty, Kazakhstan, E-mail:

More than 60 years have passed since the discovery of the Mossbauer effect. But even now, Mossbauer spectroscopy continues to develop intensively and is widely used in various fi elds of physics and chemistry, Geology and Mineralogy, biology and medicine, materials science and industry. Thus, Mossbauer spectroscopy is a powerful tool for studying the Mineralogy of iron-containing minerals and has been widely used for laboratory analysis, samples of lunar soil and meteorites. However, until 2004, no interplanetary expedition used the Mossbauer spectrometer. This situation changed with the landing of two American Rovers on Mars. The «Spirit» and «Opportunity» devices contained miniaturized Mossbauer spectrometers, which successfully worked for 90 Martian days and made a signifi cant contribution to the determination of the mineralogical features of the Martian soil. In particular, the mineral hematite was discovered, indicating the existence of water on the surface of the planet in the distant past.
Mossbauer spectroscopy allows us to determine the valence state of resonant atoms, the degree of symmetry of the crystal around them, the presence of a magnetic fi eld or electric fi eld gradient, etc. From these data, we can judge the phase composition or structure of the crystal lattice of samples.
One of the most urgent problems of modern solid state physics is related to the study of the structural state of nearsurface layers of materials. The problem is that the main physical and chemical properties of materials are determined by the state of the atoms in these layers. For example, during oxidation and corrosion, laser treatment of material surfaces, ion implantation, plastic deformation, surface modifi cation by applying thin coatings to their surface using the ion-plasma method followed by heat treatment, etc.
A large number of monographs and original articles have 004 https://www.peertechz.com/journals/global-journal-of-ecology Citation: Shokanov  been devoted to the study of the physical and chemical state of matter using Mossbauer spectroscopy with all its variety of methodological approaches [1][2][3][4][5]. It is known that the decay of a resonantly excited nucleus can occur through two channels: 1) re-emission of the resonant  -quantum; 2) internal conversion process in which, along with conversion and Auger electrons, characteristic x-ray radiation is also emitted.
In the case of the Mossbauer effect on 57 Fe nuclei, 10 Mossbauer quanta with an energy of 14.4 Kev are formed per 100 Mossbauer quanta captured by the nuclei without loss of energy for recoil due to the internal conversion of the Mossbauer transition. At the same time, 90 internal conversion electrons with an energy of 7.3 kev will be illuminated, the emission of which is accompanied by the illumination of 27 x-ray quanta of characteristic radiation with an energy of 6.4 Kev and 63 Auger electrons with energies close to 5.6 Kev. Therefore, it is possible to implement four methods for observing the resonant absorption of quanta by 57 Fe nuclei. All these methodological approaches are described in detail in the literature have their advantages and disadvantages and are used based on specifi c tasks.
In this case, the attenuation of the primary beam of γ-quanta is measured due to their interaction with the absorber containing the Mossbauer isotope (for example, 57 Fe). It should be noted that Nuclear Gamma Resonance (NGR) spectra obtained in the absorption geometry carry information averaged over the thickness of the absorber about the state of the atoms of the resonant isotope. At the same time, the absorber, for known reasons, must be of optimal thickness, which limits the applicability of the technique as a nondestructive method for monitoring the state of the sample.
The method of transmission in the methodological plan is quite simple, so it is widely used in various fi elds of science and technology. It is not surprising that most of the work using the Mossbauer effect is performed in the absorption geometry. However, to solve a number of problems, the most preferable method may be resonant scattering without recoil and secondary radiation accompanying this process. This primarily applies to the study of near-surface layers of massive samples and thin fi lms.
The pass-through EMC is used in three cases: 1) the object of the study is an absorber containing the Mossbauer isotope 57Fe, and 57Co is used as a source of gamma radiation in a paramagnetic matrix with cubic syngony; 2) a sample that does not contain the Mossbauer isotope is examined. In this case, the source of  -quanta is a radioactive preparation introduced by a known technology into the sample under study. A material with a paramagnetic cubic structure is used as an absorber. Thus, the EMC was successfully used in the study of the interaction of point defects in molybdenum and niobium by the method of nuclear gamma resonance [6].
3) the method of selective registration of Primary dislodged Atoms (PVA) and their fi nal States was implemented in the INP Kazakhstan using the u-150 isochronous cyclotron [7,8].
The method allows selectively probing small local areas of the sample, signifi cantly increasing the sensitivity of the JAG to radiation effects, and studying the structure of the material in the PVA inhibition zone. The method consists in registering the emission JAGR spectrum of the Mossbauer radionuclide 57 Co formed in the nuclear reaction of an irradiated sample. This method allows you to extend the application of JAG to objects that did not contain a Mossbauer element in the original state. A detailed description of the technique and unique results of austenitic-martensitic transformations in the PVA region of stainless steel irradiated with protons is contained in [7].
Since all of these processes are associated with the resonant absorption of -quanta, registering any of the secondary radiation can observe the effect of nuclear -resonance.
The internal conversion process is most likely to occur on K-electrons. The ratio of the number of emitted electrons to the number of emitted quanta is called the internal conversion coeffi cient, and for 57 Fe it is quite large and equal to 9.0.
In the case of a Fe absorber, the electron energy is equal to 7.3 Kev, which corresponds to an effective layer thickness of about 100 nm. Therefore, obtaining resonant spectra with registration of electron radiation, it is possible to study relatively thin layers of solids, i.e., signifi cantly expand the range of scientifi c and practical problems to be solved in comparison with the absorption method [9,11]. In addition, it is possible to obtain values of the resonant effect greater than in the absorption geometry, since the internal conversion coeffi cients of the Mossbauer transitions are relatively large.
In the middle of 70 years of the last century, these features of electronic mössbauer spectroscopy attracted the attention of researchers, and by the end of the decade, the number of published works on this technique has increased dramatically and continues to grow [12][13][14][15].
To date, several types of devices have been created for obtaining JAGR spectra with registration of conversion and associated Auger electrons. They can be divided into two groups: devices based on the selection of different energy groups from the total fl ow of electrons escaping from the absorber, as well as devices that register the integral fl ow of electrons. Each of these types of devices has its own characteristics.
For the fi rst time, Mossbauer spectra with registration of various energy groups of conversion electrons were obtained for 119 Sn in [16], and for 57 Fe in [17]. A detailed description of the spectrometer for observing nuclear gamma resonance by conversion electrons is given in [18].
The literature describes several types of mössbauer spectrometers that differ in the ways of registering conversion electrons: a) devices based on secondary electronic multipliers [19]; b) gas-discharge proportional electron detectors [20]; C) gas-discharge avalanche electron detector [21].
Citation: Shokanov  The design of a gas-discharge avalanche detector is not much different from the design of a gas-discharge proportional electron detector. The proportional detector uses tungsten as the anode material, which has a large cross-section of the photoelectric effect, which leads to the formation of nonresonant photoelectrons and, as a result, to a decrease in the resonant effect. The difference between an avalanche detector and a proportional one is due to the design of the anode and the gas fi lling. In the avalanche detector, instead of a tungsten fi lament, a beryllium plate transparent for -quanta is used as the anode. Its surface, facing the cathode, is polished. The gap (3 mm) between the cathode (test sample) and the anode is the sensitive volume of the detector. When preparing the detector for operation, the chamber was pumped out with a fore-vacuum pump and fi lled with acetone or alcohol vapors to a pressure of 80 kgf / cm 2 .
The fl ow of -quanta from the Mossbauer source passes through an aluminum foil fi lter window, then through a beryllium plate and a sensitive volume, and falls on the sample surface. Given that the detector is fi lled with gas at a relatively low pressure, the registration of  and x-ray quanta can be ignored. A low-energy electron released from the sample surface causes gas ionization, which creates an electronion avalanche in a strong electric fi eld of a sensitive volume, and in the power supply chain, the detector is a source of a voltage pulse corresponding to the electron registration act.
When the voltage at the anode increases, the counting rate increases monotonously until an independent gas discharge detailed information about the method of electron registration by a gas-discharge proportional detector can be found in [16,18]. begins in the detector. Stable operation of the detector is observed when the voltage at the anode is 10% lower than the limit. A detailed analysis of the operation of the gas-discharge avalanche electron detector can be found in [2]. Note only some advantages over other methods of detecting electrons.
In an avalanche detector, smaller electron energies correspond to larger pulse amplitudes, which causes a reduced effi ciency to register non-resonant medium-energy electrons.
Since the detector is ineffective against other types of radiation, it is possible to lower the background level, i.e. increase the resonant effect and conduct studies of radioactive samples. Figure 3 shows the spectrum of a sample cut from the spent fuel rod cover of the BN-350 power reactor with subsequent thinning to a thickness of 0.34 mm by grinding and electropolishing. Despite the high activity of the sample, it was possible to obtain a satisfactory Mossbauer spectrum via an electronic channel using a gas-discharge avalanche detector.
A methodological basis has been created for observing the resonant absorption of  -quanta by 57 Fe nuclei. It is shown that the methods of absorption, refl ection, emission and conversion Mossbauer spectroscopy allow almost without restrictions on the element composition and geometric dimensions, to study metals, alloys and chemical compounds of metallurgical, geological, mineralogical, biological and other fi elds of science and technology [22][23][24]. The created CEMS technique allows us to study iron-containing samples with a natural content of 57 Fe. It is shown that the use of CEMS signifi cantly expands the range of scientifi c and practical problems that can be solved using nuclear gamma-resonance spectroscopy.