Study of the electric quadrupole interaction at Ta impurities in rare earth metal hosts

The time differential perturbed angular correlation technique has been used to measure the electric fieldgradient (EFG) at the site of¹⁸¹Ta impurities in the heavy Rare Earth metals Gd, Tb, Dy, Ho and Er at room temperature. It is found that the ratio α ≡ ¦V _zz ^eff /V _zz ^lat ¦ between the measured EFGV _zz ^eff and the lattice EFGV _zz ^lat , which is known from lattice sum calculations, is in the order of α?300, suggesting that an important contribution to the EFG is due to electrons localized at the impurity. The ratio α is not constant throughout the Rare Earth series. It decreases from Gd to Tb and increases between Tb and Er. This behaviour is compared to the results of a previous investigation with the impurity Cd in the same hosts.     

Low-frequency dispersion of the effective transverse conductivity in inhomogeneous media in strong magnetic field

On crystalline silicon specimens with a nonuniform carrier concentration distribution produced by an optical method, a dispersion of the effective transverse conductivity σ _⊥ ^eff (ω) is observed near the frequency ω≈ω_c=τ _⊥ ^?1 ≡ε/4πσ _⊥ ^eff . At ω<ω_c, an anomalous transverse effective conductivity is observed: σ _⊥ ^eff (ω) is greater than the transverse conductivity of a homogeneous specimen σ _⊥ ^h (ω) (in the frequency range studied in the experiment σ _⊥ ^h (ω) = const). Near ω≈ω_c, the conductivity σ _⊥ ^eff decreases, and, at ω>ω_c it coincides with σ _⊥ ^h .     

Ground-state energy of quantum liquids

The kinetic (K ₄ ⁰ (n) and K ₃ ⁰ (n)) and potential (V ₄ ⁰ (n) and V ₃ ⁰ (n)) energies of ⁴He and ³He atoms have been found from the law of corresponding states and the experimental data on the dependence of the ground-state energies E ₄ ⁰ (n) and E ₃ ⁰ (n) on the density of the isotopes ⁴He and ³He. In the approximation of structureless quantum liquid, the potential energies are equal, V ₄ ⁰ V ₃ ⁰ (n) = (n), and the kinetic energies are inversely proportional to the atomic mass, $K_4^0 (n) = \frac{3} {4}K_3^0 (n)$ . The potential energy given by the expression V ⁰ = 4E ₄ ⁰ ? 3E ₃ ⁰ to a high accuracy is linear in the density n, which is associated with nearly an absence of short-range order in liquid helium. The kinetic energy of liquid ⁴He is given by the expression K ₄ ⁰ = 3(E ₃ ⁰ ? E ₄ ⁰ ), which agrees with the experimental data on neutron scattering in liquid ⁴He. The quantities K ₄ ⁰ (n) and K ₃ ⁰ (n) determine the scale of all thermodynamic characteristics in the temperature range where the effects of the particle statistics can be neglected.     

Electronic color centers in SrF2-Na crystals

It was shown that optical bleaching of M _A ⁺ color centers at 80 K in SrF₂-Na crystals causes the core of an M _A ⁺ -center to transform into the V _a ⁺ Me ⁺ V _a ⁺ configuration, in which all three point defects are arranged diagnonally in the cube cell. Reirradiation of an optically bleached crystal by x-rays generates F _D centers in it: V _a ⁺ Me ⁺ V _a ⁺ + e ^? → V _a ⁰ Me ⁺ V _a ⁺ ≡ F _D. The F _D → M _A ⁺ transformation in SrF₂-Na crystals proceeds at T = 135 K, in contrast to the F _A → M _A ⁺ transformations, which take place at T > 200 K.     

Phenomenology of composite colored weak bosons

In composite models of quarks, leptons and weak bosons whereW-constituents are colored objects, color octet partners ofW ^± andZ ⁰ are predicted. We study in detail the phenomenology of these particles. Independent of the specific model one expects a color octet isotriplet of vector bosons (W ₈ ^± ,Z ₈ ⁰ ) with mass in the range of 100–200 GeV, and a color octet isosinglet vector bosonV ₈ ⁰ with substantially larger mass, due to mixing with the gluon. Moreover, relatively light color octet excitations of the leptons appear, while the existence of “color exotic” partners of the quarks is model dependent. These particles decay mainly into a lepton (quark) and a gluon. We construct the couplings ofW ₈ ^± ,Z ₈ ⁰ andV ₈ ⁰ to ordinary and “color exotic” fermions. The signals of color octet weak bosons in low energy weak reactions are explored in detail. The production cross section ofW ₈ ^± (Z ₈ ⁰ ) in hadron-hadron collisions is calculated for \(0.54TeV \leqq \sqrt s \leqq 20TeV\) . Various decay modes of colored weak bosons are studied. The most prominent decay signatures ofW ₈ ^± andZ ₈ ⁰ are events of the type (l ^+-: charged lepton;j: hadronic jet; : missing transverse momentum). The present CERN \(p\bar p\) collider data on such events are discussed in the light ofW ₈ ^± andZ ₈ ⁰ decays. If colored weak bosons are not found with a mass less than ～250 GeV composite model building will be strongly restricted.     

The electric field gradient at the nuclear site of177Lu in Zn and In

The electric quadrupole interaction frequencyν _Q =eQV _zz /h of¹⁷⁷Lu in single crystals of Zn and In has been measured by the method of low temperature nuclear orientation. The results are $$\begin{gathered} v_Q ({}^{177}Lu\underline {Zn} ) = - 180(5)MHz \hfill \\ v_Q ({}^{177}Lu\underline {In} ) = - 19(5)MHz. \hfill \\ \end{gathered} $$ With the known quadrupole moment of¹⁷⁷LuQ=3.39 (2) b we derive for the electric field gradientV _zz (Lu Zn)=?2.20 (5)×10¹⁷ V/cm² andV _zz (Lu In)=?0.23 (6)×10¹⁷ V/cm². The results are compared with magnetostriction measurements of silver single crystals doped with rare earth atoms.     

Equations of electrodynamics with noninvariant velocity of light

A five-dimensional spaceV ^{5(t, x, c)}, in which the velocity of light c is the fifth coordinate of the event point together with the radius vectorx and time t is is introduced. The equations rot $$rot E = - \frac{1}{c}\frac{{\partial H}}{{\partial t}}; div E = 4\pi \rho ;$$ $$rot H = - \frac{1}{c}\frac{{\partial E}}{{\partial t}} + 4\pi \rho \frac{{o - Nx\dot c/c}}{{c + (1 - N)\dot ct}}; div H = 0,$$ invariant relative to the symmetry group c ₁₆₀₀ ^tf of D'Alembert's equation are constructed in the space V⁵ (E andH are the electric and magnetic fields;ν= dx/dt, c=dc/dt,N and N is a numerical parameter). The transformation properties of the electromagnetic field and the electric charge density ρ are examined for the finite group of transformationsP ₁₀ ^N ×Δ ₁ ^N ·T ₁ ^N . A theorem for adding velocities is formulated. The limiting transition to a Minkowski space M⁴(t,x)?V⁵(t, x,c) is examined.     

Electric properties of levels of 156Dy rotational bands

The nonadiabaticity of E0 transitions from 0 ₂ ⁺ states and 2 ₁ ⁺ bands in ¹⁵⁶Dy is examined within a phenomenological model that takes into account the mixing of K ^π = 0 ₁ ⁺ , 0 ₂ ⁺ , 0 ₃ ⁺ , 2 ₁ ⁺ states and 1⁺-bands. It is shown that the nonadiabaticity of E0 transitions is due primarily to the mixing of 0 ₂ ⁺ and 0 ₃ ⁺ bands.     

Fragmentation phase transition in atomic clusters IV

Within the micro-canonical ensemble it is well possible to identify phase-transitions in small systems. The consequences for the understanding of phase transitions in general are discussed by studying three realistic examples. We present micro-canonical calculations of the fragmentation phase transition in Na-, K-, and Fe- clusters of N = 200 to 3000 atoms at a constant pressure of 1 atm. The transition is clearly of first order with a backbending micro-canonical caloric curve T _P (E, V (E,P)) = {?S(E, V (E,P))/?E _P}^?1. From the Maxwell construction of β_P (E/N,P) = 1/T _P one can simultaneously determine the transition temperature T _tr, the specific latent heat q _lat, and the specific entropy-loss Δs _surf linked to the creation of intra-phase surfaces. T _trΔs _surf*N/(4πr _ws ² N _eff ^2/3 ) = γ gives the surface tension γ. Here 4πr _ws ² N _eff ^2/3 = ΣN _i*4πr _ws ² m _i ^2/3 is the combined surface area of all fragments with a mass m _i ≥ 2 and multiplicity N _i. All these characteristic parameters are for ～1000 atoms similar to their experimentally known bulk values. This finding shows clearly that within micro-canonical thermodynamics phase transitions can unambiguously be determined without invoking the thermodynamic limit. However, one has carefully to distinguish observables which are defined for each phase-space point, like the values of the conserved quantities, from thermodynamic quantities like temperature, pressure, chemical potential, and also the concept of pure phases, which refer to the volume of the energy shell of the N-body phase-space and thus do not refer to a single phase-space point. At the same time we present here the first successful microscopic calculation of the surface tension in liquid sodium, potassium, and iron at a constant pressure of 1 atm.     

Pion photoproduction on197Au to ground and isomeric states in197Hg

The lifetime of the 331.3 keV 0 ₂ ⁺ state in¹⁰⁰Zr has been measured at the gas-filled recoil separator for fission products JOSEF. By observing the delayed coincidences between theβ-particles populating the level and theE0 conversion electrons from its decay into the ground state, a half-life of 3.37±0.30 ns has been obtained. From the measured lifetime and the relative intensities of the 0 ₂ ⁺ →0 ₁ ⁺ and 0 ₂ ⁺ →2 ₁ ⁺ transitions, values of 0.493±0.015 for theE0 strength parameterρ, and of 16 single particle units forB(E2,2 ₁ ⁺ → 0 ₂ ⁺ ) have been deduced. The enhanced nature of theE0 transitions suggests mixing of the 0 ₁ ⁺ and 0 ₂ ⁺ states which may be estimated by comparing the experimentalB(E2) values for the 2 ₁ ⁺ →0 ₁ ⁺ and 2 ₁ ⁺ →0 ₂ ⁺ transitions with the predictions of the asymmetric VMI model.     

Absorptionsspektrum des Ce3+-Ions und Kristallfeld im La(Ce)Cl

The absorption spectrum of single crystals of La_(1?x)Ce _x Cl₃(x=0,05 ... 0,005) has been observed at low temperatures in the region of the 4f→4f infrared transitions. Values for the crystal-field parameters V ₂ ⁰ , V ₄ ⁰ , V ₆ ⁰ , V ₆ ⁶ and for the spin-orbit coupling constant of the ion in the crystalline environment are determined by fitting the observed splittings of the multiplet-components\({}^2F_{\tfrac{5}{2}} \) and\({}^2F_{\tfrac{7}{2}} \) in the crystal-field. The parameters are found to be consistent with values extrapolated from rare earth-ions with neighbouring atomic numbers in the same host-lattice. The only exception is the parameter V ₆ ⁶ , which is found to be smaller in La(Ce)Cl₃ than in other rare-earth-trichlorides (V ₆ ⁶ /V ₆ ⁰ =?6,23 in La(Ce)Cl₃, V ₆ ⁶ /V ₆ ⁰ ≈?10 in other trichlorides). The correct relation V ₆ ⁶ /V ₆ ⁰ in La(Ce)Cl₃ is obtained by fitting the parameters to the observed crystal-field-splitting of the\({}^2F_{\tfrac{5}{2}} \) — component and to the observed Zeeman-splitting-factors taken from the literature. The discrepancies between the two fitting procedures are explained by an effect of nonlinear shielding of the crystal-field.     

Estimation of the QED coupling constant α at\sqrt s = M_Z

LEP measurements of theZ ⁰ parameters have been used to estimate the value of QED coupling constant at theZ ⁰ mass. The estimated value α _eff ^-1 (M _Z )=128.2±0.9 _-0.4 ^+0.0 (M _top) is in good agreement with the expectation of 128.0 _?0.4 ^+0.2 from the Standard Model.     

Magnetische Eigenschaften von wasserfreiem Cer- und Praseodymchlorid

The results of susceptibility measurements on single crystals of anhydrous CeCl₃ and PrCl₃, published in a preceeding paper, are analysed in terms of a static crystalline electric field of approximate D_3h symmetry acting upon the Ce³⁺ and Pr³⁺ ions. For each of the two salts a set of crystal field parameters V ₂ ⁰ , V ₄ ⁰ , V ₆ ⁰ , V ₆ ⁶ was adjusted to fit the susceptibility data. To get agreement within experimental accuracy a small reduction of the Landég _J-factors had to be introduced, indicating the influence of factors which are omitted in the simple crystal field model, presumably covalent bond and configurational interaction.     

Gyromagnetic ratios of excited states in186W

The gyromagnetic ratios of the 4 ₁ ⁺ , 6 ₁ ⁺ , and 2 ₂ ⁺ states in¹⁸⁶W were measured relative to that of the 2 ₁ ⁺ level by means of the transient field implantation perturbedγ-ray angular distribution technique. The nuclei in the states of interest were Coulomb excited using a beam of 220-MeV⁶³Cu projectiles and recoiled swiftly through a thin, polarized Fe foil. The present measurements yielded ratiosg(4 ₁ ⁺ )/g(2 ₁ ⁺ )=1.04±0.07,g(6 ₁ ⁺ )/g(2 ₁ ⁺ )=1.03 ±0.20 andg(2 ₂ ⁺ )/g(2 ₁ ⁺ )=0.63±0.13. The sizable disparity between the measuredg-factors of the ground- and excited-band is examined within the context of the interacting boson approximation model.     

An ESR study of NH 3 + , al center and HO2 · radical in alkali feldspars

Paramagnetic centers of NH ₃ ⁺ , Al, and HO₂ · have been observed in alkali feldspars from Aichi prefecture, Japan. The quartet signal has been tentatively ascribed to NH ₃ ⁺ rather than to ·CH₃, although the hyperfine splitting by¹⁴N (I=1) was not observed. The averageg- andA-valuesg _av=2.0033 andA _av ^H =2.45 mT, respectively, were attributed to hydrogen. The powder spectra of Al centers stable up to 400 K were simulated by the anisotropicg factors ofg _zz =2.060,g _xx =2.0014,g _yy=2.0021 andA=0.9 mT. Newly discovered HO₂ · is stable up to 570 K. The intensities of the spectra from NH ₃ ⁺ and Al centers were enhanced by gamma-ray irradiation, while that of HO₂ · was not enhanced. Production efficiency,G-value (radical/100 eV) of NH ₃ ⁺ has been obtained to beG=0.01. These results suggest that ESR dating of feldspars is possible.     

Paramagnetische Resonanz des dreiwertigen Gadoliniums in YPO4, YVO4 und YAsO4

The EPR spectra of Gd³⁺-doped isostructural single crystals of YPO₄, YVO₄, and YAsO₄ have been measured in X-band at room temperature and at nitrogen and helium temperatures. The zero-field splitting can be described by the five crystal-field parametersb ₂ ⁰ ,b ₄ ⁰ ,b _6/0,b ₄ ⁴ , and b ₆ ⁴ fitted to a tetragonal spin-Hamiltonian corresponding to the point symmetry D_2d of the Gd³⁺ site. The values ofg and b ₂ ⁰ vary significantly with host lattice and with temperature.     

Microscopic foundation of the interacting boson model in thes d-shell nuclei

Starting from an isospin invariant shell-model hamiltonian, we describe a method for deriving microscopically the IBM-hamiltonian appropriate to lights d-shell nuclei. The key ingredients of our approach are:a) the Belyaev-Zelevinsky-Marshalek (BZM) bosonization procedure;b) two successive unitary transformations that extract the “maximally decoupled” collective bosons with angular momentaJ=0(s _ππ ⁺ ,s _νν ⁺ ,s _πν ⁺ ) andJ =2(d _ππ ⁺ ,d _νν ⁺ ,d _πν ⁺ (T=0),d _πν ⁺ (T=1)). The method is applied to obtain the low-energy spectra and the electron scattering form factors for the 0 ₁ ⁺ →2 ₁ ⁺ transitions in²⁰Ne and²⁴Mg. Good agreement with the exact shell-model results is achieved. The inclusion of proton-neutron bosons (s _πν ⁺ ,d _πν ⁺ (T=1),d _πν ⁺ (T=0)), as well as the renormalization of boson parameters due to the non-collective degrees of freedom, are shown to play a crucial role.