Synchrotron Mössbauer source of57Fe radiation

A nonradioactive source of Mössbauer radiation is described for use in Mössbauer absorption and scattering spectroscopy. The radiation is generated by synchrotron Xrays in an iron borate single crystal set in diffraction conditions at the Néel temperature (75.3°C). Like a conventional Mössbauer source the new Synchrotron Mössbauer (SM) source emits singleline radiation of about natural linewidth, but in addition the emitted radiation is fully recoilless, highly directed and of pure linear polarization. An extremely high suppression of the electronic scattering is achieved. The latter circumstance allows one to perform Mössbauer experiments using pulsed synchrotron radiation in a steady state mode as in a normal Mössbauer measurement.The theory of the SM source is developed. First Mössbauer spectra obtained with the SM source are shown. Applications of the SM source are discussed.     

ИЗОТОПЫ ФТОРА F19 И F21 В МОДЕЛИ НИЛЬССОНА

Energy levels and electromagnetic properties of fluorin isotopes in the Nilsson's model with Coriolis mixing are investigated. Position of the F¹⁹ levels is satisfactorily explained up to the energy of 4·5 MeV. Concerning the F²¹ it seems that the shell model will better correspond to the F²¹ nucleus.

---

---

. , .     

Investigation of Rust Formed on Steel Surfaces and Related Oxyhydroxides

In order to indentity the corrosion products formed on steel surfaces from ⁵⁷Fe Mössbauer spectroscopy, detailed Mössbauer parameters have been determined for various kinds of iron-oxyhydroxides: -FeOOH, -FeOOH, -FeOOH and -FeOOH. ⁵⁷Fe Mössbauer measurements of the iron oxyhydroxides indicate the following results. Fe occupies a single site in -FeOOH, but below the Néel temperature as at e.g., 300 K the Mössbauer spectrum is always broad, showing a distribution of the strength of the magnetic exchange interactions. Its shape depends on the grain-size and synthetic methods of the specimen. Fe occupies 3 sites in -FeOOH. High-purity reagents of -FeOOH always contain small amounts of -FeOOH and their Néel temperatures depend on the synthetic methods of the specimen. Mössbauer spectroscopy of the synthetic -FeOOH shows very broad distribution of the hyperfine magnetic fields.     

Methodological imperfection and formalizations of scientific activity

Any mathematical formalization of scientific activity allows for imperfections in the methodology that is formalized. These can be of three types, dirty, rotten, and dammed. Restricting mathematical attention to those methods that cannot be construed to be imperfect drastically reduces the class of objects that must be analyzed, and relates all other objects to these more regular ones. Examples are drawn from empirical logic.     

Some Remarks on a Nongeometrical Interpretation of Gravity and the Flatness Problem

In a nongeometrical interpretation of gravity,the metric g(x) = + (x)is interpreted as an effective metric, whereas(x) is interpreted as afundamental gravitational field, propagated in spacetime which isactually flat. Some advantages and disadvantages of suchan interpretation are discussed. The main advantage isa natural resolution of the flatness problem.     

Mössbauer spectrum of an ensemble of57Fe nuclei interacting with radiation fields coupling the Zeeman sublevels of the nuclear excited 3/2 state

We have introduced the concept dressed nucleus in order to describe the interaction of a nucleus (in a static magnetic field) with a radiation field havingn photons of a certain mode. The idea is to consider the global system as one quantum system in the Schrödinger representation. The number of eigenvalues of the Hamiltonian of the global system is (2I+1)², withI the spin of the free nuclear state. Taking into account the form of the corresponding eigenvectors and the relevant selection rules, the total number of -transitions (for the nuclear transition 3/2^- 1/2^-) is 24. If a Mössbauer effect experiment is set up with a single-line absorber, the source being an ensemble of dressed nuclei, we would expect a spectrum showing 24 lines, whose relative positions and intensities are calculated.     

The Mössbauer effect and magnetism

The Mössbauer effect enabled the magnetic hyperfine splitting (hfs) in ferromagnetic solids to be observed directly for the first time. It was quickly extended to measurements on antiferromagnets, ferrimagnets and paramagnets, and is now well established as a probe for the study of magnetic materials. Applications have ranged from the old problem of the state of the iron atoms in ferromagnetic alloys to the new magnetic materials, e.g. amorphous magnets, spin glasses, fine particle magnets and multilayers. Some examples where the Mössbauer effect has made an important contribution are described.     

Nano-structured materials

The term nano in connection with crystalline or amorphous structures represents important materials from a scientific as well as from a technical point of view. In addition, it seems that, so far, Mössbauer spectroscopy is the most successful technique for obtaining information on these structures. A brief overview of the perspective which Mössbauer spectroscopy affords in the study of the structure of such materials is presented.     

Mean-Field Critical Behavior for the Contact Process

The contact process is a model of spread of an infectious disease. Combining with the result of ref. 1, we prove that the critical exponents take on the mean-field values for sufficiently high dimensional nearest-neighbor models and for sufficiently spread-out models with d>4:()– _c as _c and ()( _c–)^–1 as _c, where () and () are the spread probability and the susceptibility of the infection respectively, and _c is the critical infection rate. Our results imply that the upper critical dimension for the contact process is at most 4.     

Feynman integral and complex classical trajectories

Let _t be an analytic solution of the Schrödinger equation with the initial condition . Let _t be the solution of the Schrödinger equation with the initial condition =, where is an analytic function. When 0, then _t (x) _t (x)¹ ( _t (x)), where _t (x) trajectory starting from x. We relate this result to Feynman's sum over trajectories and complex stochastic differential equations.     

57Fe Mössbauer studies in a new cluster spin glass system RuxFeGa (0.5≦x≦1.5)

⁵⁷Fe Mössbauer and bulk magnetization studies have been carried out in a new magnetic system Ru_xFeGa for 0.5x1.5. The system is seen to freeze into a cluster spin glass phase at 70 K. The freezing temperature and the hyperfine field at Fe at the lowest measured temperature, 190 kOe, is essentially same for all values of x investigated.     

ИЗЛУЧЕНИЕ ЭЛЕКТРИЧЕ СКОГО ДИПОЛЯ НАД ГРАН ИЦЕЙ ДВУХ СРЕД

, , . , - - . - . -, - , . , - ; , , .     

A new high frequency “relaxation window” for measuring molecular field fluctuations

We report a new Mössbauer relaxation window which allows the fluctuation rate of a molecular field acting on an impurity in a strongly correlated spin system to be obtained. For a molecular field of 1 T, the fluctuation rate can be measured up to 10 THz, which is three orders of magnitude higher than for the classical relaxation window. The calculated line shapes show that Ising-like fluctuations of the molecular field can be distinguished from other types of fluctuations (in-plane or in space). An application and some other possible uses of this new relaxation window are discussed.     

Cation distribution and entropic disordering in mixed spinel ferrite Ga0.4Fe0.6NiCr1−yAlyO4

Mössbauer measurements (4.2T298°K) indicate the presence of entropic disordering in (Ga _0.4 ³⁺ Fe _0.6 ³⁺ Al _p ³⁺ )[Ni²⁺Cr _1–y ³⁺ Al _y-p ³⁺ Fe _p ³⁺ ]O₄ and a linear increase in p with y between 0(y=0) and 0.11(y=1). Entropic spins are located only on A-sites indicating relatively large A-sublattice frustration. Weak A-B coupling could explain this separate sublattice behaviour. Magneton number, alongwith Mössbauer p values, shows B-site canting which increases with y revealing weakness of A-B interaction. Present system can be called a frustrated ferrimagnet or entropie ferrimagnet where ferrimagnetic and frustrated (entropie) spins are coexisting.     

Mössbauer spectroscopy in physical metallurgy

In this anniversary contribution the natural and intimate match making which occurs between the two star performers-⁵⁷Fe in Mössbauer spectroscopy and iron in physical metallurgy—is described by selecting typical examples reflecting the author's interest: phases, f.c.c. -Fe, defects, diffusion and amorphous metals.     

On the theory of ferromagnetic thin films

As is known, the second approximation in the calculation of the partition function by the traces method of ferromagnetic thin films gives wrong results for the coordination number equal to eight. In order to obtain correct results even for this case, the third order approximation of the partition function is developed and thus the magnetic properties of body-centred cubic iron thin films are studied. The dependence of the Curie temperature on the thickness, for different values of the ratio between the anisotropy constant and the exchange energy between two neighbours, is discussed. A value can be chosen for this ratio such that the thin film becomes ferromagnetic only for a thickness greater than a definite value.

---

, . , , (Fe). . , - .

     

SYNFOS

An expression for the amplitude of a pulse of synchrotron radiation coherently scattered in the forward direction by a Mössbauer absorber consisting of randomly oriented paramagnetic ironcontaining molecules (for example, a frozen solution of a ⁵⁷Fe protein) in an applied magnetic field is derived from the theory of optics. It is assumed that the hyperfine splittings present in the Mössbauer nuclei can be described in the framework of the spinHamiltonian formalism. In the general case of a thick Mössbauer sample of this kind the response on an incident monochromatic and fully polarized beam cannot be given analytically because of the integrations involved. How nuclear forwardscattering for this general case is evaluated in the program package called SYNFOS is outlined.     

Mössbauer (237Np) and structural studies of some oxouranates and oxoneptunates

Two oxoneptunates have been investigated using²³⁷Np Mössbauer spectroscopy. The crystal structures of Na₂U₂O₇ and -Na₂UO₄ were recently determined by one of us. The two isotypic compounds Na₂Np₂O₇ and -Na₂NpO₄ were prepared. For -Na₂NpO₄ the Mössbauer spectrum confirms the structural study. For Na₂Np₂O₇ the structural study enabled the fit of the complex Mössbauer spectrum recorded at 77K.     

ТЕМПЕРАТУРНАЯ ЗАВИС ИМОСТЬ ТЕРМОЭЛЕКТРОДВИЖУЩ ЕЙ СИЛЫ СЕРОГО ОЛОВА С ПРИМЕСЯМИ КАДМИЯ

- , - —183 —10 °.