Search for instantaneous radiation near the instant of break momentum of various fissioning nuclear systems at low excitation energies

The main results of studying the properties of “instantaneous” neutrons and γ photons during the fission of ^{233, 235}U(n _th, f) and ²³⁹Pu(n _th, f) nuclei and spontaneous fission of ²⁵²Cf, which were performed on the WWR-M reactor at the St. Petersburg Nuclear Physics Institute, Russian Academy of Sciences, are presented. Along with obtaining the main characteristics of the instantaneous radiation from fission fragments, these studies were also aimed at gaining deeper insight into such exotic processes as the emission of break neutrons and γ photons from a fissioning nucleus near the break point. These investigations were performed on different experimental setups using different analytical methods. This approach allowed us not only to find but also to reduce to minimum possible systematic effects. The yields of break neutrons were found to be about (5–7) × 10⁻² of the total number of neutrons per ^{233, 235}U(n, f) fission event and approximately twice as much for ²³⁹Pu(n, f) and ²⁵²Cf. The coefficient of T-odd asymmetry for γ photons is in agreement with the estimate obtained on the assumption that the observed effect is mainly related to the γ photons emitted by excited fragments with highly oriented angular momenta. This fact gave grounds to conclude that the desired break γ photons cannot be reliably selected (within the obtained experimental accuracy) against the much larger background of γ photons from fission fragments.     

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An ellipsoidal model of colour centers in photochromic glass was proposed to explain an additional absorption spectrum. Absorption spectra of small ($\text{R ? 100}\text{A}\text{?}$) involving oblong and oblate ellipsoids of rotation have been analysed. The splitting of the absorption spectrum of the small silver particles with non-spherical form resulted in an absorption spectrum different from that for spherical particles. Calculation of the absorption spectra of the system of oblate ellipsoids with considerable dispersion in eccentricity and of about 20 Å in size was in good agreement with experiment. Absorption spectra of the system of oblong ellipsoids differed significantly from experimental findings, indicating that oblong particles were absent. To verify the basic theory of the colour center model, advanced experiments have been carried out on the bleaching of photochromic glass by monochromatic polarized light. The so called photo-adaptation effect has been found, that is, the absorption decreased faster at the wavelength of the bleaching light. The photo-adaptation spectral width indicated that the particle size was nearly 20 Å. The ratio of changing absorption for perpendicular and parallel orientations of bleaching and reading polarization vectors was about 0.7 in the longwave visable range, indicating that the colour were substantially anisotropic.In the thermal recovery of photochromic glass the shortwave and longwave absorptions were bleached faster, indicating the lower stability of the strong oblate particles, which specifies absorption in those parts of the spectrum.     

The Orientational Optical Non-Linearity of Liquid Crystals

Abstract

The cubic optical non-linearity of a cholesteric liquid crystal (CLC) having a planar helical texture is considered. A study was made of an effect which has a minimal establishment time and is due to the change in the director distribution along the helix under the orientational influence of the light field. Polarisation peculiarities of the non-linearity, when the light wave propagates along the helical axis, are discussed. Self-focusing should not occur for circulary polarised light, but has the constant ?₂ ～ 8.10^?8 cm³/erg for linearly polarised light. The additional rotation of the axes of elliptical polarisation is predicted to be proportional to the light intensity and determined by the same constant ?₂; this rotation is identical for both right-and left-handed CLC. Non-linear optical activity is absent in the approximation under consideration.

Analogous effects for light propagating through an oriented nematic are discussed.     

Effect of Ampoule Rotation on Growth of InGaAs Ternary Bulk Crystals from Solution

In_xGa_1-xAs (x = 0.045) ternary bulk crystals were grown on GaAs seeds from an In–Ga–As solution by the temperature-difference method modified to rotate a growth ampoule. The effect of ampoule rotation on the profiles of the composition and the growth rate were investigated. The In compositional profiles were uniform irrespective of the ampoule rotation. On the other hand, the growth rate at the center of the crystal increased from 40 μm/h at 0 rpm to 55 μm/h at 100 rpm. The profile of growth rate changed from concave to convex toward the seed due to the ampoule rotation. Flow patterns and compositional profiles in the solution were simulated by solving four equations: Navier-Stokes, continuity, energy, and solute diffusion. The ampoule rotation enhanced the transportation of As component from the GaAs feed toward the seed at the central region in the solution. This led to the increase of the growth rate.     

Efficient and practical method for the synthesis of hydrophobic azines as liquid crystalline materials

A series of hydrophobic symmetrical azines: 1,2-bis[4-(n-alkoxy)benzylidene]hydrazine (where, n-alkoxy: O(CH₂)_nH, n = 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 16, or 18) have been prepared following an efficient and practical method. These compounds have been synthesized via the condensation reaction of hydrazine hydrate and appropriately 4-(n-alkoxy) benzaldehydes in acidic medium under ambient conditions. The prepared organic compounds have been characterized and their structures were elucidated depending upon micro-elemental analysis and spectral data (IR, UV-Vis, ¹HNMR, ¹³C{¹H}NMR, 2D ¹H-¹H-cozy, 2D ¹H-¹³C-HSQC, and mass spectra). Liquid crystalline behavior of the prepared compounds was studied using polarized light optical microscopy and differential scanning calorimetry techniques. This study revealed that all the compounds displayed enantiotropic liquid crystal properties, exhibiting smectic and nematic mesophases.     

Reliability of high‐resolution electron backscatter diffraction determination of strain and rotation variations using phase‐only and cross correlation

This contribution analyzes the reliability of strain and rotation variation determination using cross‐ as well as phase‐only correlation of experimental wide‐angle electron backscatter diffraction (EBSD) patterns. For both rotation and three‐point bending the resulting displacement gradient tensor components are examined in terms of magnitude and statistical scatter as a function of various correlation procedure parameters and signal‐to‐noise ratio. It is shown that on the one hand the Fourier filter width has a major impact on the strain results. At higher noise level a smaller filter width has to be applied for obtaining maximum precision. On the other hand, the influence of the degree of overlap of the regions of interest positioned in the patterns is less important. For both rotation and bending experiments the cross‐correlation variant yields a smaller standard deviation with respect to phase‐only correlation, in particular for elevated noise level. The difference is attributed to the stronger propagation of noise effects in the course of phase‐only correlation function calculation and fitting. In the rotation experiment a standard deviation of ∼1.0 × 10⁻⁴, averaged over the displacement gradient tensor components, and a rotational precision of ∼1.5 × 10⁻⁴ rad have been achieved by using optimized evaluation settings.     

New selective nickel(II)-N3 nitrogen bond in adenine: Synthesis and structure of [(tren) (adenine) (monochloro)nickel(II)] chloride and [(tren)(imidazole)(monoaqua)nickel(II)] dichloride

With the aim to obtain further insight into the nature of the Ni(II)-nitrogen bond in complexes with nucleobases, we have synthesized two novel Ni(II) ternary complexes constituted by Ni(II), tris(2-aminoethyl)amine (tren) and neutral adenine (AdH) or imidazole (ImH). The reaction of NiCl₂·6H₂O with tren and imidazole yields the ternary [Ni(tren)(ImH)(H₂O)]Cl₂·H₂O complex and the same reaction with adenine instead of imidazole gives the ternary [Ni(tren)(AdH)Cl]Cl complex. The complexes have been studied by spectrophotometric and spectroscopic measurements and by X-ray diffraction. The ternary complex of adenine is monoclinic, space groupC2/c, and exhibits a pseudo-octahedral geometry, being Ni(II) coordinated to the four nitrogen atoms of the tetradentate tren ligand, to a Cl^– ion and to the pyrimidine N3 site of a neutral adenine. Such an exclusive Ni-N3 bonding [2.081(4)Å] is now reported for the first time. The ternary complex of imidazole is monoclinic, space groupP2₁/n. Its pseudo-octahedral geometry is similar to that found in the above adenine complex although a water molecule instead of a Cl^– ion is now present in the coordination sphere. In fact, Ni(II) is coordinated to tetradentate tren, to the imidazole N1 nitrogen and to a water molecule. Electronic and¹H NMR spectra in solution indicate that the octahedral structures found in the solid state are substantially maintained in solution. Furthermore, the present investigation suggests that the adenine Ni-N3 and imidazole Ni-N1 bonds have the same chemical nature, involving mainly - and only partially-bonding. The Ni-N3 bonding is discussed in connection with biological implications and possible applications.     

Calorimetric and phase equilibria studies of the Ni–Sn–Bi system

The phase equilibria at 1273 K were investigated and an isothermal section of the Ni‐Sn‐Bi phase diagram was constructed. The phase boundaries are inclined to the Bi‐rich region that is agreement with phase equilibria at lower temperatures. The molar enthalpies of formation of liquid ternary Ni–Sn–Bi alloys have been determined at 833, 873 and 933 K by direct reaction calorimetry using pellets of 325 mesh powders of pure Ni, Sn and Bi. Measurements were performed with alloys containing from 0.05 to 0.10 mole fractions of nickel, and at ratios of tin and bismuth mole fractions X_Sn/X_Bi = 2.8, 1.2 and 0.43. The experimental calorimetric data were used to calculate a regular solutions parameter of the ternary liquid phase by means of two different thermodynamic data files. It was found that the Ni–Sn–Bi ternary liquid phase could be described as temperature independent ternary regular solution. The assessed values of the ternary interaction parameter are ‐280 J·mol^–1 and 56 000 J·mol^–1, depending on the binary parameters used. Enthalpies of formation of solid binary phases were measured, too. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Calculations of homogeneous region in Ga1−xAlxAs and GaAs1−xPx ternary solid solutions

Ternary solid solutions of A^IIIB^V compounds are considered as pseudobinary A(x)^IIIB(x)^v compounds, where the behaviour of A(x)^III and B(x)^v pseudoatoms is quite similar to A^III and B^v atoms in a binary A^IIIB^v crystal. Weak dependence of point defect contribution into Gibb's energy of A^IIIB^v crystal on its defect nature, random character of ternary solid solutions of A^IIIB^v compounds allow to use already for binary compounds developed formalism in the determination of component thermodynamic potentials of solid solution. Basing on literature data for the equilibrium solidus of AlAs the approximation for the temperature dependence of thermodynamic potential of an AB quasimolecule in A^IIIB^v crystal is revised. This result together with the well-known parameters for the equilibrium liquidus in Ga–P, Ga–As, and Al–As systems were used for calculations of the nonstoichiometric factor at the boundary of a homogeneous region in Ga_1−xAl_xAs and GaAs_1−xP_x ternary solid solutions. The results are compared with the known literature data.     

Infrared lattice vibrations of PbGa2S4

Infrared reflectivity spectra of PbGa₂S₄ single crystals are measured at room temperature in the wavenumber range from 30 to 4000 cm⁻¹ for the polarization directions E ∥ c and E ∥ b. The frequencies of 13 B_1u modes and 11 B_2u modes are derived from the spectra. The results are compared with previous studies and with lattice vibration data of ternary chalcopyrite and defect-chalcopyrite compounds.     

Structure of the pinacol formed via sodium-promoted reductive dimerization of 12-methyleneheptacyclo-[6.6.02,6.03,13.04,11.05,9.010,14]tetradecan-7-one

The pinacol resulting from sodium promoted reductive coupling of a methyleneheptacyclo-[6.6.0^2,6.0^3,13.0^4,11.0^5,9.0^10,14]tetradecanone possesses a conformation in which equivalent groups on the pinacol carbon are virtually perpendicular to each other. This rotation minimizes steric interactions, thus the geometries of all the fragments in the molecule are within expected values.     

Enhancement of magneto-optical kerr rotation by magnetoactive dielectric structures

The analytical expressions that describe the transformation of an arbitrarily polarized optical radiation in periodic magneto-optical structures are derived. It is established that the magnetic-field-induced splitting into two components of the frequency ranges of the resonance interaction of light with a magnetoactive structure corresponding to circularly polarized eigenwaves provides considerable enhancement of the rotation of the polarization plane of the reflected radiation. The expedience of using a dielectric mirror located behind the magnetoactive structure is shown. Such a mirror allows one not only to preserve the considerable enhancement of the rotation but also provides the total reflection of light.     

Comparison of lead solubility in NaCl crystals from data obtained by different methods

The solvus of the NaCl: Pb²⁺ system was found in the concentration range from 1.5 × 10⁻³ to 1.9 × 10⁻² mol% at temperatures ranging from 375 to 430 °C from the data of flotation measurements of the crystal density. The heat of impurity dissolution equal to 2.0 ± ± 0.6 eV and the change in the vibrational entropy in the formation of the solid solution S_v/K= 20 ± 10 were determined. Reasons for a difference in the estimates of lead solubility in NaCl, obtained from temperature dependences of light scattering and by other methods: measurement of the density, electric conductivity, and the electron-microscopic decoration of the same crystals are discussed.     

Effect of Cu Ions on the Dipole Moments and Polarization of Strontium Barium Niobate Single Crystals

The crystal growth, the ferroelectric hysteresis loops, and the infrared reflectivity spectra of coppermodified strontium barium niobate (SBN) single crystals are reported. Compared with the undoped SBN crystals, the copper-modified crystals have stable hysteresis loops, the spontaneous polarization of which is about 0.30 C/m², but that of the undoped SBN crystals is only about 0.12 C/m². Their coercive field strength is all about 340 V/mm. The experimental results of the infrared spectra show that the infrared reflectivities vary as the orientations of the dipole moments owing to the copper-doping. The c-axis becomes the most stable orientation of the dipole moments, and the polarization will be locked and won't recede if the copper-modified crystals are polarized into monodomains.     

Combinatorial approach to the simulation of superstructures of the NaCl type

The combinatorial approach is used to simulate superstructures of the NaCl type. An algorithm for searching for possible models of superstructures is developed which includes alternating the occupation of the metal sublattice by chemically different cations in an isolated cubic fragment. The application of this algorithm to small cubic fragments is demonstrated. The models are compared with known complex metal oxides (binary A-B-O and ternary A-B-C-O compounds).     

Optical Properties,Conductivity and Structure of the DTT-TCNQ CT Complex

Abstract

The crystal structure, the optical spectra and electrical conductivity of dithieno(3,2-b; 2′,3′-d)thiophene-tetracyanoquinodimethane (DTT-TCNQ) charge-transfer complex have been measured. DTT-TCNQ crystallizes in the monoclinic space group P2₁/c with a = 7.206(2), b = 7.574(2), c = 32.324(9), β - 92.18(4)°, Z - 4, and the donor and acceptor molecules are arranged in alternated stacks.

The low conductivity (a = 10^?2 S cm^?1 for the single crystal, along the stacking axis a) is characteristic of a semiconductor with activation energy of .61-.76 eV, and is related to the alternate stack structure.

Despite the poor condctivity of the DTT-TCNQ CT complex we estimated, from structure and IR data, a low degree of ionicity (p = .2–.3) which characterizes the DTT molecule as an interestign donor.

The polarized IR spectra shows the effect of vibronic activation of some of the a_g modes of TCNQ.     

Dielectric properties of binary and ternary mixtures of alcohols: Analysis of H-bonded interaction in complex systems

The heterogeneous H-bonded interactions in mixtures of glass-former liquids, i.e., binary mixtures of ethyl alcohol (EA) with ethylene glycol (EG) and ternary mixtures of equi-molar EA + EG system with glycerol (Gly) have been investigated at 21 concentrations by using precisely measured values of static and high frequency limiting dielectric constants at 25 °C. Concentration dependent observed negative values of excess dielectric constant (ε^E) and effective Kirkwood correlation factor (g^eff) implies the formation of H-bonded complexes between EA and EG molecules which reduces the effective number of dipoles. The EA + EG system forms the strongest complexes corresponding to the molar ratio ∼1:1. The observed positive ε^E values of the (EA + EG) + Gly ternary mixtures confirm the increase in number of effective dipoles contributed to the dielectric constant values due to the formation of the ternary complexes. Critical analysis of the experimental results of the EA + EG and the (EA + EG) + Gly mixtures suggest the suitability of ε^E and g^eff study in order to explain the dipolar ordering mechanism formed during the complexes between the alcohol molecules in their ternary mixtures.     

Raman spectrum and structure of solid P2Cl4

The Raman spectrum of liquid and solid polycrystalline P₂Cl₄ has been recorded from 30 to 700 cm^–1. The far infrared spectrum of the solid has also been reinvestigated. From these data, it is necessary to reassign the P-P stretch (a _g), the PC1₂ rock (a _u) and the PCl wag (b _u). Three lattice modes were observed in the Raman spectrum whereas none was found in the infrared spectrum. No correlation field splitting was observed for any of the intramolecular fundamentals. Although the vibrational data for the crystalline state is best interpreted in terms of atrans (C _2h, 2/_m) conformation, there is some evidence that another form may be present, in small amounts, in the fluid states. Furthermore, no evidence for the torsional mode, previously assigned at 91 cm^–1, has been found and calculations have been made which indicate that such a frequency would lead to an un-acceptably high barrier to internal rotation of the asymmetric PC1₂ rotor.Taken from the thesis of J. E. Saunders which has been submitted in partial fulfillment of the Ph.D. degree.     

Optical and chiro-optical properties of crystals with sillenite structure

The experimental data on the optical and chiro-optical properties of crystals with the sillenite structure Bi₁₂ M _xO_{20 ± δ} (M= elements of II–VIII groups) have been reviewed. The relations between the changes in the chemical composition, the crystal structure of Bi₁₂ M _xO_{20 ± δ} compounds, absorption, circular dichroism, and optical rotation spectra of sillenites have been established. A model taking into account the contribution of the electronic transitions of optically active tetrahedral [MO₄] ^n? complexes to the total optical rotation in sillenites is suggested. The data on the state (oxidation degree) and the recharging processes of 3d-elements in sillenites are systematized. The models of optical centers responsible for the photochromic effect in sillenites are critically analyzed.     

Molecular and crystal structures of halopentaamminerhodium-(III) complexes, [Rh(NH3)5Cl]Cl2 and [Rh(NH3)5Br]Br2

The crystal and molecular structures of the title compounds have been determined by three-dimensional single-crystal X-ray techniques. All crystallographic details are fully reported. The major chemical conclusion for the pair, [Rh(NH₃)₅Cl]Cl₂ and [Rh(NH₃)Br]Br₂, is that neither Cl nor Br exert a static intramoleculartrans effect. Furthermore, the two halogens have the same static electronic structural effect on the [Rh^III(NH₃)₅] fragment. The conclusions shed much light on spectroscopic, thermodynamic and kinetic data of other compounds.Work supported in part by NSF-traineeship (E.A.H.).The term trans effect will be employed to refer to static and kinetic behavior-the distinction will be apparent from the context of the discussion.