Frequency reference for atomic transitions of Rb D<Subscript>2</Subscript>-line based on the effect of selective reflection

On an example of the D₂-line of the Rb atoms the work of the frequency reference of atomic transitions is demonstrated, based on the application of the spectrum of a selective reflectance (SR) from the boundary of atom vapors with the use of nano-cell (NC) with the thickness L ~ λ/2, where λ is the laser wavelength equal to 780 nm. When changing the thickness of the nano-cell near the thickness L ~ λ/2, we observe the inversion of sign of the SR slope profile which is positive when L < λ/2 and negative when L > λ/2. In the case when the incidence angle of the laser beam on the surface of the nano-cell is close to the normal, in real-time it is possible to form the derivative of the SR which represents a resonance peak with ~35 MHz spectral linewidth and located at the atomic transition. The phenomenon of oscillation of the sign of slope while changing the nano-cell thickness from L ~ λ/2 up to L ~ 3/2λ is demonstrated. The practical application of the SR is noted.     

Sorption behavior of tritiated water on Armenian natural zeolites

Summary The sorptive behavior of tritiated water on natural, irradiated, chemically treated and heated at high temperatures Armenian zeolites was studied and their capacity for the separation and enrichment of tritiated water was evaluated. The distribution coefficients from the batch experiments were calculated for different zeolites and vary between 0.23 and 3.01. The influence of temperature, acidity, basicity, specific activity, electron and gamma-irradiation on sorption has been studied.     

Two strongly contrasting Λ-systems in the <Emphasis Type="Italic">D</Emphasis> <Subscript>1</Subscript> line of <Superscript>87</Superscript>Rb in a transverse magnetic field

Four different types of spectroscopic cells that cover all possible existing versions of sealed-off cells (containing alkali atomic vapor) characterized by drastically different relaxation rates γ_rel are used to study the electromagnetically induced transparency spectra of two Λ-systems in the D₁ line of ⁸⁷Rb in the presence of transverse magnetic field. Two cw narrowband diode-lasers are used to form the coupling laser radiation (with a fixed frequency) and the probe radiation with a tunable frequency. Two strongly contrasting Λ-systems are found: the first shows resonances that are transformed from dark resonances to bright resonances in all cases apart from nanocells, whereas the second shows four dark resonances in all four different types of cell. The theoretical simulations are in good agreement with the experimental results.     

Magnetic collapse and the change of electronic structure of FeBO3 antiferromagnet under high pressure

The effect of high pressures up to 60 GPa on single-crystal and polycrystalline samples of iron borate ⁵⁷FeBO₃ was studied by Mössbauer absorption spectroscopy (⁵⁷Fe nuclei) in a diamond anvil cell. Magnetic field H _hf at the ⁵⁷Fe nuclei increases with pressure but abruptly drops to zero at 46±2 GPa, indicating the crystal transition from the antiferromagnetic to nonmagnetic state. This is accompanied by an abrupt change in the isomer shift and quadrupole splitting. Their values in the high-pressure phase are evidence for the transition of Fe⁺³ ions from a high-spin (S=5/2, ⁶ A _1g ) to low-spin (S=1/2, ⁶ T2g) state (spin crossover). This correlates with an abrupt decrease in the unit-cell volume (by ～9%) and optical gap. The change of the magnetic and electronic structures is explained by Mott’s transition with rupturing of strong d-d-electron correlations.     

Equation of state and structural phase transition in FeBO3 at high pressure

The evolution of X-ray diffraction patterns in FeBO₃ under high pressures up to 63 GPa has been investigated at room temperature in a diamond anvil cell. A structural phase transition at a pressure of 53±2 GPa was found for the first time. The transition is of the first-order type with a hysteresisless drop of the reduced unit cell volume of about 8.6%. Apparently, the transition is isostructural. At pressures below the transition, the equation of state for FeBO₃ was fitted. In the third-order approximation of the Birch-Murnagan equation of state, the bulk modulus K and its first pressure derivative K′ were found to be 255±25 GPa and 5.0±1.2, respectively.     

Doppler-free satellites of resonances of electromagnetically induced transparency and absorption on the D 2 lines of alkali metals

The peculiarities of intra-Doppler structures that are observed in the atomic absorption spectrum of alkali metals with the help of two independent lasers have been studied. These structures accompany ultranarrow coherent resonances of electromagnetically induced transparency and absorption. With the D ₂ line of rubidium taken as an example, it is shown that, in the scheme of unidirectional waves, the maximum number of satellite resonances caused by optical pumping selective with respect to the atomic velocity is equal to seven, while only six resonances are observed in the traditional scheme of saturated absorption with counterpropagating waves of the same frequency. The spectral position of the resonances and their polarity depend on the frequency of the saturating radiation, while their number and relative amplitude depend also on the experimental geometry. These features are of general character and should show themselves in the absorption spectrum on the D ₂ lines of all alkali metals. An explanation of these features is given. The calculated spectral separations between the resonances are compared to the experimental ones, and their possible application is discussed.     

Splitting of the electromagnetically induced transparency resonance on 85Rb atoms in strong magnetic fields up to the Paschen-Back regime

Electromagnetically induced transparency (EIT) resonance in strong magnetic fields of up to 1.7 kG has been investigated with the use of a 30-??m cell filled with an atomic rubidium vapor and neon as a buffer gas. The EIT resonance in the ?? system of the D₁ line of ⁸⁵Rb atoms has been formed with the use of two narrowband (??1 MHz) 795-nm diode lasers. The EIT resonance in a longitudinal magnetic field is split into five components. It has been demonstrated that the frequencies of the five EIT components are either blue- or red-shifted with an increase in the magnetic field, depending on the frequency ??_P of the probe laser. In has been shown that in both cases the ⁸⁵Rb atoms enter the hyperfine Paschen-Back regime in magnetic fields of >1 kG. The hyperfine Paschen-Back regime is manifested by the frequency slopes of all five EIT components asymptotically approaching the same fixed value. The experiment agrees well with the theory.     

Preparation of 3-substituted 5-acetyl-N-(<Emphasis Type="Italic">β</Emphasis>-hydroxyethyl) pyrrolidones

Previously unknown 5-acetyl-3-alkyl-N-(β-hydroxyethyl)pyrrolidones have been synthesized by the reaction of γ-acetyl-α-alkylbutyrolactones with ethanolamine, and their semicarbazones and acetyl derivatives have been obtained.     

Profinitely generated Γ-modules

Theorems of homological definiteness of arbitrary -modules are proved which generalize similar results proved earlier for -modules of special type.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 86, pp. 157–161, 1979.