Experimental determination of the difference of the beta-decay constants for atomic and molecular tritium

The results of an experiment measuring the difference Δλ=λ_a−λ _m of the beta-decay constants of atomic and molecular tritium are reported. The difference Δλ is determined by comparing the rates of growth of the relative content of radiogenic helium-3 in samples containing atomic and molecular tritium. The result Δλ=(4.6±0.8)×10⁻¹²s⁻¹ corresponds to a relative change of the decay constant by ∼0.26%. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 3, 167–170 (10 August 1998)     

Elastic interaction potential in solid solutions with cubic symmetry

On the basis of a microscopic approximation, within which three parameters of interatomic binding (according to the number of elastic constants of a cubic crystal) are taken into account, an approximation for the coefficients of the expansion has been obtained for the elastic interaction potential in vs elastic constants of a cubic crystal. An analysis of the kind of dependencies of the expansion coefficients on the direction has been carried out. It has been shown that can have an accidental saddle anomaly in planes of the type 110, in addition to extrema in high-symmetry directions of the type <100>, <110>, <111>. Coefficient B always takes negative values for bcc crystals near <100> directions. An approximation has been found for the elastic interaction potential vs elastic moduli of a cubic crystal, starting from a microscopic approach.Translated from Izvestiya Vysshikh Uchebnykh Zavenenii, Fizika, No. 2, pp. 20–24, February, 1982.     

Lattice constants of Langmuir-Blodgett films measured by atomic force microscopy

Langmuir-Blodgett (LB) films are examples of soft organic and related biological samples. Therefore it is essential to make sure that the mechanical scanning process does not disturb the specimen. We describe atomic force microscopy measurements of the lattice constants of Cd arachidate LB films. A lattice constant d_hk is revealed correctly by scanning parallel to the corresponding lattice line [hk]. Scanning in deviating directions enlarges the lattice spacing. The phenomena are explained with a simple model. Previous studies where such artefacts have not been reported are discussed.     

Calculation of the cubic symmetry force constants of methyl bromide and methyl chloride

The cubic symmetry force constants have been calculated for methyl bromide and methyl chloride through the method developed by Hoy et al. (Mol. Phys. 24, 1265–1290 (1972)). The spectroscopic constants recently reported in the literature have been utilized for the present analysis. Out of a total of 38 independent cubic force constants, 6 and 10 constants were constrained to zero for a methyl bromide and methyl chloride, respectively, in which a diagonal force constant of F₆₆₆ was included for both molecules. However, it is noted that those force constants which are only concerned with the A₁ symmetry coordinates have been determined independent of the constraint for both of these molecules.     

Determination of the cubic force field of nitrosyl fluoride by vibration-rotation α constants and sextic centrifugal distortion constants

Summary The rotational spectra of ONF in the (100), (010) and (001) excited vibrational states were observed and the corresponding vibrationratation α constants determined. A centrifugal-distortion analysis of 156 ground-state rotational transitions yielded accurate values of all the sextic centrifugal-distortion constants. Both vibration-rotation α constants and sextic centrifugal-distortion constants were used to determine, by least-squares methods, the cubic part of the general valence force field of nitrosyl fluoride. Anab initio calculation provided reliable constraints for the three cubic terms of the potential-energy function which are not directly determinable by the available experimental data. Supporting organizations: C.N.R. and M.P.I.     

The determination of anisotropy constants from torque curves — II

This is an extension of a previous paper which examined the methods available for the determination of the anisotropy constant from torque curves when the anisotropy is governed by a single constant i.e. E = K₁ sin²φ. The two methods singled out in that paper as being of special merit are briefly re-examined when the anisotropy energy takes the form E = K₁ sin²φ + K₂ sin⁴φ.     

Direct determination of born — von Kármán force constants for face-centred cubic elements from measured phonon frequencies

Born — von Kármán force constants are shown, by refining a procedure developed recently, to depend linearly on certain squared phonon frequencies. A 17x17 matrix of coefficients in such linear equations for crystals with the copper structure is given. An illustrative example (Pd) exhibits good agreement with reliable published model force constants; moreover, a higher degree of precision has probably been obtained. Some problems concerning extensions of the procedure to other structures and to more realistic lattice-dynamical models are outlined.The author wishes to thank J. Bok and D. Frei for valuable technical assistance.     

Precise lattice constants determination of cubic crystals from x-ray powder diffractometric measurements

An analytical method for precise determination of lattice constants of cubic crystals, from x-ray diffractometric measurements, was formulated. The method minimizes both systematic and random errors and enables the estimation of the uncertainties in the constants. For higher precision, a weighting factor may also be used.The method was applied to diffractometric data from a Si powder standard reference material and was considered to be highly reliable for precise measurements.     

Experimental determination of third-order elastic constants of diamond

To determine the nonlinear elastic response of diamond, single crystals were shock compressed along the [100], [110], and [111] orientations to 120 GPa peak elastic stresses. Particle velocity histories and elastic wave velocities were measured by using laser interferometry. The measured elastic wave profiles were used, in combination with published acoustic measurements, to determine the complete set of third-order elastic constants. These constants represent the first experimental determination, and several differ significantly from those calculated by using theoretical models.     

Effects of atomic size on antiphase boundary energy in solid solutions

The energy of an antiphase boundary has been calculated by means of Pines's elastic spheres method, as modified by incorporating the dependence of atomic size on the neighbors in the first coordination sphere, which represents an advance in the theory of ordered solid solutions. There is a reduction in the elastic strain energy when a nonequilibrium antiphase boundary is formed in CuZn, and if this is incorporated one obtains realistic values for the energies of such boundaries; in AuCu₃ the elastic strain energy increases the energy of an antiphase boundary of octahedral type. The change in the elastic strain energy in a nonequilibrium antiphase boundary constitutes a considerable part of the total energy change given by the quasichemical theory, and it introduces substantial corrections into the antiphase-boundary energy for CuZn and AuCu₃.     

Lattice vibrations and local order in substitutional solid solutions. II

The nearest neighbour effect on the mean vibrational state is investigated in solid solutions. It is shown that the possibility of A-B pair bond affection in the closest surrounding of the bond is accounted for, when linear, parabolic or some more complicated dependence of the states of A and B atoms on the relative proportions of both types in their first coordination shell is used. The expression is deduced for the mean vibrational state of atoms in the solid solution under the assumption that the dependence of A and B atom states on the number of unlike atoms in the first coordination shell is given as a polynomial ofi-th order. In the case of the parabolic approximation it follows that the structure of the solid solution (i.e. degree of order) is given by atom interactions, which result in configurations with maximum lattice cohesion. There is no assumption about the nature of atom interaction in the present paper. Therefore the results combined with experimental data can serve as a criterion of availability of different physical models and help in a better understanding of atomic bonds in metal systems.     

Temperature dependence of the elastic constants of single-crystal KI-KBr solid solutions

Elastic constants C₁₁, C₁₂, and C₄₄ were measured for solid KI-KBr solutions over the temperature range 20–280 °C. When plotted as functions of the composition, elastic constants C₁₁ and C₄₄ display a significant deviation toward a negative nonadditivity. The Debye temperature calculated from the elastic constants at 0 °K is 8 ° lower than the additive value at compositions containing 66 M% KI.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 58–62, April, 1971.In conclusion the authors thank A. A. Botaki for the opportunity to measure the elastic constants.     

The local atomic structures in Si1−x Ge x random solid solutions

The local structures of Si_1?x Ge _x solid solutions can be described with FDUC model (the five distorted unit cells) based on a phenomenological valence force field approach. Bond lengths and strain energies in these solid solutions can be predicted. The distorted feature of the local structure is well described by the five distorted unit cells. Calculated results are compared with those obtained from EXAFS, indicating the excellent agreement between theoretical predictions and EXAFS measurements with the largest divergence not larger than 0.01 Å. In addition, The relationship betweenSi _1?x Ge _x and III–V random solid solutions is also discussed.     

Quantitative determination of contact stiffness using atomic force acoustic microscopy

Atomic force acoustic microscopy is a near-field technique which combines the ability of ultrasonics to image elastic properties with the high lateral resolution of scanning probe microscopes. We present a technique to measure the contact stiffness and the Young's modulus of sample surfaces quantitatively, with a resolution of approximately 20 nm, exploiting the contact resonance frequencies of standard cantilevers used in atomic force microscopy. The Young's modulus of nanocrystalline ferrite films has been measured as a function of oxidation temperature. Furthermore, images showing the domain structure of piezoelectric lead zirconate titanate ceramics have been taken.