The decay of the isomeric state of yttrium 87 has been reinvestigated by using scintillation and Ge(Li) spectrometers. This work leads to the conclusion for its half life to be 12.5 hours instead of 14 hours obtained in the previous study. A weak branching of a beta ray with a maximum energy of 1.54 MeV was found. It was assigned to be a direct transition from the isomeric state (1g_9⁄2) of yttrium 87 to the ground state (1g_9⁄2) of strontium 87. This allowed transition was found to be comparatively hindered and its logft value obtained was 7.6. Its branching ratio was found to be (6.2±1.2)×10⁻³. An end-point energy of a beta ray from the ground state of yttrium 87 was found to be 0.78 MeV. Its logft value was 6.2. The 1.54 MeV beta branching was discussed qualitatively in terms of the pairing theory.

View full abstract

NiO crystals free from twin structure were prepared by annealing at 1650°C in argon atmosphere and either by axially cooling through the Néel temperature with a temperature gradient set along [111] or by applying a stress along [111] at room temperature. Torque measurements were made at various temperatures and in magnetic field up to 17 kOe. The results show that in the axially cooled crystal irreversible motion of S-walls, separating antiferromagnetic domains of different spin axes, takes place above 2 kOe for the field component in the (111) plane, and above 2.4 kOe the whole crystal forms nearly a single antiferromagnetic domain. In the stressed crystals these field values are higher. In both these crystals the torque in the [111]-rotation has a dominant sixfold component at high fields, which has the same magnitude for both crystals but is interpreted as being due to crystal imperfections. MnO was also studied and similar results were obtained.

View full abstract

The specific heat and the magnetic susceptibility of ferric ammonium alum at very low temperatures are investigated theoretically. The calculated results are in good agreement with the recent specific heat measurement by Vilches and Wheatley with use of appropriate crystalline field parameters for this salt. The results are also compared with the magnetic susceptibility data with a satisfactory agreement.

View full abstract

The effect of magnetic field on the spin density wave based on the one-band model is studied with respect to two points, one the instability of the ferromagnetic state at high fields by a perturbing infinitesimal spin density wave and the other the susceptibility of a helical spin density wave for a field perpendicular to the plane of the spin rotation. The instability occurs by a helical or sinusoidal spin density wave whose oscillation is perpendicular to the magnetization. The corresponding critical field is calculated as a function of the intra-atomic Coulomb integral U for various values of the Fermi radius k_F. The perpendicular susceptibility is also calculated for the same parameter values.

View full abstract

Electron spin resonance of Fe³⁺ and Mn²⁺ ions in antiferromagnetic FeCl₂ was investigated at low temperatures using various microwave frequencies and pulsed magnetic fields. Experimental results show that these impurities in FeCl₂ occupy mainly the substitutional position and couple with host Fe²⁺ spins by rather weak exchange interaction. Using the metamagnetic properties of FeCl₂, these resonances were investigated both above and below the critical field H_c. The intralayer and interlayer exchange field H₁ and H₂ of these impurities were found by analysis to be
H₁(AF)=8.0 kOe H₂(AF)=4.2 kOe for Fe³⁺ spins,
H₁(F)=21.6 kOe H₂(AF)=13.8 kOe for Mn²⁺ spins,
where AF and F mean the antiferromgnetic and ferromagnetic exchange interactions with Fe²⁺ spins, respectively. Interstitial impurity spin resonance was also found and the exchange interaction with neighboring Fe²⁺ spins is estimated.

View full abstract

The magnetic susceptibility and the electrical resistivity of dilute Au–V alloys, between 0.3 and 2.0 at.% of vanadium are measured in the temperature range from 1.4°K to 1000°K. The temperature variation of the magnetic susceptibility follows the Curie-Weiss type formula μ²⁄3k(T+A), where A is 290±10°K. The electrical resistivity of the solute varies logarithmically at the high temperature and becomes parabolic, 1−(T⁄B)² with B=280°K∼310°K, at the low temperature limit. These observations are independent of vanadium concentrations. The above experimental facts are discussed in comparison with the recently reported theories of the s-d interaction. The Kondo temperature is found to be about 300°K.

View full abstract

The behavior of the Hall coefficients and the electrical resistivities of α-phase alloys of copper and silver can be explained by formulae similar to those for the two band model. Anisotropic Fermi surface is divided into electron- and hole-like parts and the change of the energy gap with alloying is neglected. The calculated Hall coefficient vs. electron-atom ratio curves show the same type of minimum which was observed by Köster et al. The concentration dependence of the resistivity is shown to be a form ρ=ρ₀+CZ²(D−x)x, where ρ₀ is the resistivity of pure noble metal, Z and x are the relative valency and the atomic fraction of solute, C and D are constants for a given temperature. Also it is suggested that the qualitative explanation of the thermoelectric power of these alloys is possible.

View full abstract

Momentum distributions of annihilating electron pairs have been measured along the [111] axes of copper and copper-aluminium alloys. Each curve shows a fairly distinct hump near the (111) zone face, being in marked contrast with the theoretical expectation of Berko and Plaskett. (Phys. Rev. 112 (1958, 1877) It is pointed out that the cause of the failure of this theory consists in the assumption that the positron wave function is a constant.

View full abstract

A new method which is useful for the study of Fermi surface has been developed in positron annihilation. The two photons emitted from a rota-table specimen are detected by a pair of counters fixed at a collinear position (θ=0), and the coincidence counting rate is recorded as a function of the azimuthal angle \varphi of the specimen around the rotation axis.
The usefulness of the present method for the study of Fermi surface has been demonstrated by a measurement on copper single-crystals. Several merits of the new method are pointed out. Some applications to the case of θ\ eweq0 are discussed.

View full abstract

The microwave radiation of 4 GHz was emitted at 77°K from a bar of n-InSb with axis parallel to [110] direction, when it was subjected to an electric field of about 30 V/cm, with or without the magnetic field. The detected microwave emission consisted of a number of spikes and amplitude-modulated with the acoustoelectric oscillation. The length of the sample enough to emit the microwave radiation was about 1 cm in accordance with the minimum length for exciting the acoustoelectric oscillation. The application of the transverse magnetic field enhanced the microwave emission and as for its electric and magnetic field dependence there were close correlations between the microwave emission and acoustoelectric effect. Finally the microwave emission of n-InSb at the low field is concluded to be due to the build-up of phonons caused by the piezoelectrical coupling.

View full abstract

Two step current saturation was observed in CdS. The first saturation is well described by the theoretical calculation based on the classical sound amplification mechanism of TWT type introduced by White. While, the second saturation may be interpreted qualitatively by the quantum mechanical phonon amplification mechanism due to Cerenkov like radiation introduced by Yamashita and Nakamura. At the transients of the both saturations a current oscillation was observed. The oscillation of the first saturation may be caused by the natural vibration of the crystal, and the second damped one may be due to the non-linear property of the quantum mechanical coupling.

View full abstract

The formation and decay of color centers in alkali halides have been studied using a pulsed electron beam. The F and V-type bands reach maximum heights in optical density at the end of the radiation pulse. V_k and V₁ bands in KBr appear to show the first order decay kinetics; their room temperature life times are 1.3 and 3.8 μsec, respectively. A fraction of F and F′ bands bleach by the annihilation with migrating V_k centers. The activation energies for the disappearance of H, V₁ and V_k centers in KBr are found to be 0.09, 0.25 and 0.39±0.02 eV, respectively. A fraction of H centers in KCl decays with a temperature independent time constant (∼0.13 μsec) which is due to the tunneling with nearby F centers. In crystals containing U-centers (H⁻ ions) the F band continues to grow for several microseconds after the pulse. Absorption bands which decay with the same time constant as the F band growth have been found at 775 mμ (KBr) and 725 mμ (KCl).

View full abstract

The reflectivity between 6 eV and 12 eV and the absorption tails both in the intrinsic region and in the impurity bromine band region of KCl single crystals are studied as a function of temperature in the range 10°K to 573°K. The absorption measurement complements the earlier results reported in 1960 and 1961 in improving the wavelength scale and in extending the temperature range. The present data allow us to investigate the phonons interacting with Γ-exciton, yielding hω=1.42×10⁻² eV (for (3/2, 1/2-component)) and =1.59×10⁻² eV (for (1/2, 1/2)-component)) for phonons effective to the peak shift and hω=1.47×10⁻² eV for phonons taking part in the optical absorption processes in the intrinsic Urbach tail. The temperature dependence is presented on the absorption constant spectra up to 12 eV and dispersion spectra n up to the Γ-exciton region, each being derived by the Kramers and Kronig analysis with the use of the above data.
The data of the absorption tail position E(10^α) at A=10^α cm⁻¹ (α: a constant) and the peak position E(A_max) for the (3/2, 1/2)-component are summarized for all the alkali halides investigated in different places up to the present. An analysis of the data indicates that the difference in energy E(A_max)−E(10^α) is nearly independent on the individual species of alkali halide for the intrinsic Urbach tail at any temperature.

View full abstract

The magnetic and optical properties of the U₂-center have been theoretically studied. Starting from the many-electron formulation of the problem, its reducibility to one-body problem is discussed. The reducibility is determined by the approximation employed for the many-electron wave function and the physical quantity considered.
Numerical calculation is carried out in terms of the wave function with correlation effect as well as with the overlapping effect between orbital wave functions. It has lead to a good result for the hyperfine (hf) constants of the nearest neighbor ions and the g-shift. But it gives an overestimate for some quantities of farther ions. This result is in contrast with that of the approach from the orthogonalization procedure only. Quadrupole interaction constants and the oscillator strength for the optical U₂-band are also calculated.

View full abstract

The allowed and forbidden ESR lines of Mn²⁺ in CaSO₄ have been studied. The observed hyperfine constants (A_z=−99.1 gauss, A_x=A_y=−99.7 gauss) indicate strong ionicity of this crystal. The expressions for the separations of the forbidden doublets in the M=±3⁄2↔±1⁄2 transitions were obtained and compared with the experimental results. The intensity of the forbidden transitions due to cross terms (Remark: Graphics omitted.) was found to obey (sin2\varphi)² rule.

View full abstract

In the luminescence spectra of Eu³⁺ in SrTiO₃, two kinds of vibronic structure, i.e., rather sharp satellite lines (vibronic lines) and asymmetric bands (vibronic tails), were found to exist. The tails were observed also in the spectra of Tb³⁺ and Pr³⁺ in SrTiO₃. The tail strongly appears associated only with transitions allowed by forccd electric dipole. A comparison of the luminescence spectra of Eu³⁺ in SrTiO₃ and BaTiO₃ has suggested the existence of a correlation between the strength of vibronic structure and the site symmetry of rare earth ions. To investigate this, the luminescence spectra of Eu³⁺ were studied in various perovskite type oxides in which the site symmetry of Eu³⁺ varies from O_h to very low symmetries. It has been clarified that the vibronic lines strongly appear when the site symmetry is O_h or very close to it. However, the vibronic tail was observed only in SrTiO₃. In order that the vibronic tail appears, some special properties of host material seem to be required.

View full abstract

Widths and shapes of the three groups of absorption lines in ruby are measured in the 77–500°K temperature range. Temperature-dependent linewidths are successfully interpreted in terms of the direct and Raman relaxations. The observed asymmetric shapes of the B₃ and R₃′ lines are shown to be due to the energy dependent one-phonon relaxation rate.
Non-empirical calculations are made on transition probabilities and stress-induced changes in level splittings of the t₂³²E₁, ²T₁ and ²T₂ states. Orbit-lattice parameters are evaluated using point charge model with Watson’s Hartree-Fock function for a free Cr³⁺ ion. Mixing of all the doublet states with d³ electron configuration is taken into account. Agreement between calculation and experiment is surprisingly good.
Cubic symmetry approximation and point charge model are shown to be very good. Some slight discrepancies between the calculated rates and experiment are explained by the deviation of the Debye model from a more realistic phonon spectrum deduced from the vibronic structure associated with the R lines.

View full abstract

Foil specimens of about 3μ in thickness were directly stretched inside a 500 kV electron microscope, and the dynamic behaviors of dislocations were continuously observed.
When the specimens are deformed, frequency of cross slip is increased with increasing amount of deformation, and a number of small prismatic dislocation loops are formed. Mechanical and thermal stability of these loops are related to their size; i.e., small ones are fairly stable mechanically but unstable thermally. Therefore, distribution and size of the loops depend on stress, deformation temperature, and strain rate. Movement of dislocations is retarded by these loops, and dislocations often tangle around them. At regions where dislocations tangle, the loop density is increased with the increase of deformation, so that escape tendency of tangling dislocations from the loop forest is decreased. Finally the cell boundaries are formed around these loop forest, while dislocations still can move forward through the cell boundaries by repeating cross slip. Work-hardening process is closely correlative to these phenomena.
When the deformed specimens are annealed, the dislocation loops disappear in the regular order of their size, and then many of tangling dislocations in cell boundaries come loose. This fact shows a good correlation with the deformation process mentioned above.

View full abstract

The mean free path of high energy electrons for the plasmon excitation has been measured in a single crystal of aluminium by a Möllenstedt type energy analyser combined with an electron microscope. The mean free path of 50 kV electron is 1000±100Å when the crystal is far away from the exact Bragg condition to the incident electrons. When the crystal is near the exact Bragg condition to the incident electrons, an anomaly in the mean free path was observed. The mean free path was 900±100Å and 1100±100Å when W>0 and W<0 respectively, where W is a parameter showing the deviation from the exact Bragg condition.
This result indicates that there are two mean free paths corresponding to the two Bloch waves, i. e. The Bloch wave on the branch-1 has the shorter mean free path than that on the branch-2.

View full abstract

Based on the quantum theory of X-ray diffraction by a perfect crystal (M. Ashkin and M. Kuriyama, J. Phys. Soc. Japan 21 (1966) 1549), a diffraction theory for a distorted crystal has been developed. The scattering amplitude for the case of a single Bragg reflection has been obtained in terms of a lattice sum including the displacement of each atom. A basic assumption for this formulation is that there is no overlap of the electron wave functions of the displaced atoms. The existing basic assumption in the dynamical theory for a distorted crystal, that the local distortion in the crystal must change very slowly so that the local wave field can be described by the dynamical theory for a perfect crystal, has been successfully avoided in the present formulation. A criticism is also made of the so-called “Fourier” expansion of polarizability or electron distribution in the distorted crystal, which has been important for the dynamical theory.

View full abstract

Accurate lattice parameters of the tetragonal phase of VO₂ have been determined as a function of temperature by X-ray powder method in the temperature range 78°C to 415°C. Both the lattice parameters are found to increase with increasing temperature, the relative increase in the ‘c’ parameter being greater than that in the ‘a’ parameter. Using the data the coefficients of thermal expansion, α_|| and α_⊥, have been calculated by a graphical method. Temperature dependence of the coefficients are represented by the following equations:
α_||=29.638×10⁻⁶−2.930×10⁻⁸t+2.576×10−¹¹t²
α_⊥=5.828×10⁻⁶−7.091×10⁻⁹t+6.946×10−¹²t²,
where t is in °C.

View full abstract

Inelastic atom-atom collision is investigated under semi-classical condition by the use of perturbed stationary state method. Wave functions of the perturbed states of the system are expanded in terms of products of wave functions of isolated atoms. The expression for cross-section is derived, using these wave functions. Dependence of the cross-section on velocity is discussed. Further it is shown that the cross-section is expressed only in terms of the exact adiabatic potentials concerned. The obtained formula is applied to electron capture by α particles in hydrogen. Results of calculation are discussed and compared with the experimental data by Fite et al.

View full abstract

The change of molecular size distribution of polymers induced by crosslinking is solved rigorously when the initial distribution is uniform. The behaviour of moments of the distribution after gelation is also discussed. Further, a simple relation between number and weight average degree of polymerization (Remark: Graphics omitted.) is found.

View full abstract

The change of molecular size distribution of polymers induced by crosslinking is obtained in the case when the initial distribution is Poisson’s type.
The behaviour of it near the gel point when p is large is given by m(p,t)∼p^−5⁄2. For the Schulz-Zimm distribution, some conjecture about the asymptotic behaviour of the size distribution is given.

View full abstract

Some significant features of the scattering of slow positrons by a molecule, as distinct from electron scattering, are discussed. As an example, comparison is made between the electron and positron cross sections for rotational excitation of the hydrogen and nitrogen molecules calculated in the Born approximation.

View full abstract

An instability criterion of a plasma with an axially symmetrical velocity distribution for transverse waves propagating perpendicularly to the axis of symmetry is derived by means of a Nyquist-diagram technique in the absence of an external magnetic field. When the distribution of particles of type j is denoted by F_j(v_x²+v_y², v_z), the criterion of instability can be written as
(Remark: Graphics omitted.)
where ω_j is the plasma frequency of the j-th type of particles. This criterion is applied to several examples.

View full abstract