IsoscalarE2 transition strengths in 10≦A≦48 nuclei

Electric quadrupole transition strengths for the 2 ₁ ⁺ ,T=1→0 ₁ ⁺ ,T=1γ-decay branches are summarized for 10≦A≦42 nuclei. In¹⁰B the corresponding branch has been remeasured by use of the⁹Be(p, γ)¹⁰B resonance reaction atE _p =320 keV; an upper limit of 0.6% is found. The variation of theE2 strengths within each individualT=1 isobaric multiplet reveals the particleor hole-character of the levels involved. The isoscalar 2 ₁ ⁺ →0 ₁ ⁺ transition strengths in 10≦A≦48 nuclei vary between 2 and 20 Weißkopf units showing drastic shell effects. Results for the ratio of neutron and proton matrix elements deduced from analogγ-decay studies and from inelastic pion scattering are compared.     

Untersuchung des Zerfalls von134Cs durch γ-γ-Winkelkorrelationsmessungen

γ-γ-angular correlation measurements with Ge(Li) detectors and NaJ(Tl) detectors provided theE2/M1 mixing ratios of the following gamma transitions: 3 ₁ ⁺ →2 ₂ ⁺ (475.3 keV), 2 ₂ ⁺ →2 ₁ ⁺ (563.3 keV), 4 ₂ ⁺ →4 ₁ ⁺ (569.4 keV), 3 ₁ ⁺ →2 ₁ ⁺ (1,039 keV). The angular correlation measurements were only consistent with spin 3 of the 1,643 keV level. The half life of the 1,401 keV level was determined by delayed coincidence techniques to beT _1/2 (1,401 keV)≦30 ps.     

About the nature of Ni3+ magnetic centres in the LaSrAl1−xNixO4 ceramics

LaSrAl_1?x Ni _x 0₄ (x≤0.11) ceramics werer studied by EPR. It was established that Ni³⁺ ions in this compound may be in two states: a low spin one with t _2g ⁶ e _g ¹ electron configuration and high spin state with t _2g ⁵ e _g ² electron configuration. It was shown that the random distribution of La³⁺ and Sr²⁺ ions in the heavy metal sublattice leads to two kinds for each type of these centres with different degree of tetragonal distortions. The total concentration of NiO₆ isolated centres in these ceramics does not exceed 5–10 % of a total number of nickel ions at a givenx. A model, explaining these peculiarities observed in an experiment by the enhanced tendency of Ni³⁺ ions to clusterization, was proposed. It appears that even at small concentrations Ni³⁺ ions form clusters and conglomerates, whose structural characteristics of the oxygen octahedra are comparable with those in LaSrNiO₄.     

Photoemission on the highT c superconductors Y−Ba−Cu−O

XPS and UPS photoemission experiments on the highT _c superconductors (T _c ≈90 K) with nominal composition YBa₂Cu₃O_9-y (y≈2) show the following:

1. The density of electronic states at the Fermi energy is very small, much smaller than in pure Cu.
2. The Cu 2p spectra show only a Cu²⁺ contribution.
3. The Ba core levels show a structure with two components of nearly equal magnitude, which leads to the suggestion that these compounds have large O^2? vacancies coordinated to Ba²⁺ sites.
4. Annealing at 400°C under UHV conditions leads possibly to a partial reduction of Cu²⁺ to lower Cu valence states and to a small increase of the O^2? vacancy component of the Ba²⁺ line.

     

Statistical mechanism of the formation of the energy spectra of sputtered molecular clusters

The energy spectra of Si _n O _m ^? clusters sputtered from Si targets by Xe⁺ ions with O₂ pumping onto a bombarded surface, as well as by O ₂ ⁺ ions, are studied. It is shown that the form of the Si _n O _2n+1 ^? energy distributions does not depend on the experimental conditions. Significant differences in the energy spectra of O and Si monomers as compared to Si _n O _2n+1 ^? clusters are revealed. The mentioned features of the energy distribution of Si _n O _m ^? clusters are explained within the framework of the statistical recombination mechanism of their formation in combinatorial synthesis processes.     

On the existence of crossing symmetric and unitary scattering amplitudes with Regge poles

We give a complete proof of the existence of scattering amplitudesA(s,t,u) with the following properties

1. the amplitudes are total symmetric ins,t, andu.
2. they satisfy elastic unitarity for 4≦s≦16, and
3. they develop resonances forl≧2 on a bounded Regge trajectory which dominates the asymptotics for large energies.

     

Photoluminescence quenching in zinc oxide modified by Al2O3 and Al2O3 · CeO2 Nanopowders under proton irradiations

The photoluminescence spectra of initial ZnO powder and that modified by Al₂O₃, Al₂O₃ · CeO₂ nanopowders are investigated in the range 360–660 nm before and after 100-keV proton irradiation. It is found that the introduction of nanoparticles causes a decrease in the UV-band intensity and a change in the luminescence bands in the visual spectrum due to V _O ⁺ oxygen vacancies, O _int ^- interstitial oxygen, and V _Zn ^- zinc vacancies. Luminescence quenching in the UV and visible spectra occurs under the effect of protons. The decomposition of the spectra into elementary defects and analysis of changes in their integrated intensity during modification and irradiation of the powders are carried out.     

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.     

The ϕ 2 4 quantum field as a limit of Sine-Gordon fields

We exhibit the λ? ₂ ⁴ quantum field theory as the limit of Sine-Gordon fields as suggested by the identity $$\varphi ^4 /4! = \mathop {\lim }\limits_{\varepsilon \to 0} (\varepsilon ^{ - 4} \cos \varepsilon \varphi - \varepsilon ^{ - 4} + \tfrac{1}{2}\varepsilon ^{ - 2} \varphi ^2 ).$$ The proofs of finite volume stability for the two models, due to Nelson and Fröhlich respectively, are unrelated. We find a generalized stability argument that incorporates ideas from both of the simpler cases. The above limit, for the Schwinger functions, then proceeds uniformly in ?. As a by-product, let (?,dμ) be a Gaussian random field, ? _K (1≦κ<∞) a regularization of ?, andV a function satisfying:

1. V(? _K )≧?ak ^α
2. ∥V(?) ?V(? _K )∥ _p≦bp ^β k ^?γ, 2≦p < ∞

Thene ^?V(?)∈L ¹(dμ) provided α(β?1)<γ.     

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.     

Excitation of bands of the first negative system of the N 2 + ion in collisions of N+ and O+ ions with N2 molecules

Absolute values of the excitation cross sections of the (0,0) bands [for O⁺(⁴ S), O⁺(² P)-N₂ pairs] and the (0,0), (0,1), (1,2), and (2,3) bands [for N⁺(³ P)-N₂ pairs] of the first negative system of the N ₂ ⁺ ion have been measured in collisions with nitrogen molecules of nitrogen and oxygen ions in the ground state and in a metastable state in the interval of ion energies 1–10 keV. The process of excitation of the (0,0) band of the first negative system of the N ₂ ⁺ ion by oxygen ions in the metastable ² P state is of a quasi-resonant character. The presence in the beam of ions in metastable states was monitored by measuring the excitation efficiency of the (0,0) band λ3914 Å of the N ₂ ⁺ ion in different operating regimes of the highfrequency ion source. For N⁺ ions in the ³ P ground state, as the collision frequency is decreased the relative vibrational population of the v′=1 and v′=2 levels of the B ²Σ _u ⁺ state of the N ₂ ⁺ ion is observed to deviate strongly from the value calculated in the Franck-Condon model.     

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.     

Jump discontinuities of semilinear,strictly hyperbolic systems in two variables: Creation and propagation

The creation and propagation of jump discontinuities in the solutions of semilinear strictly hyperbolic systems is studied in the case where the initial data has a discrete set, {x _i } _i ⁼¹ⁿ , of jump discontinuities. LetS be the smallest closed set which satisfies:

1. S is a union of forward characteristics.
2. S contains all the forward characteristics from the points {x _i } _i ⁼¹ⁿ .
3. if two forward characteristics inS intersect, then all forward characteristics from the point of intersection lie inS.

We prove that the singular support of the solution lies inS. We derive a sum law which gives a lower bound on the smoothness of the solution across forward characteristics from an intersection point. We prove a sufficient condition which guarantees that in many cases the lower bound is also an upper bound.     

Electrodynamics of rotating planetary plasmaspheres in a dipole magnetic field

As a model of the actual structure of the planetary plasmasphere, we consider the electrodynamical problem of electric field and current generation by a planet with a dipole magnetic field corotating with the plasma envelope. The plasma envelope is characterized by the conductivity and angular velocity of the magnetospheric plasma as functions of the distance τ from the planet center and the angle ? measured from the rotation axis. The exact solutions of the Maxwell equations are obtained in the axially symmetric case within the framework of unipole electrodynamics when the rotational and magnetic axes coincide. These solutions describe the possible distributions of electric fields, currents, and charges in the rotating plasma envelope surrounding the magnetized planet. As an exmple, we constructed, using the theory proposed, the exact solution corresponding to the following structure of the plasmasphere:

1. the plasmasphere region corotating with the planet and located between L-shells (L=τ/Rsin ² ?, where R is the radius of the planet) from L=1 to L=L_*;
2. the polar region with differential, spherically symmetric rotation;
3. the transient region of the plasmasphere rotating differentially with the angular velocity dependent on the L-number and located between L-shells from L=L_* to L=L_*+L₀;
4. the external (vacuum) region.

Analysis of the multipole expansion of the electrostatic potential showed that the electric field potential is equal to zero in the external region (L>L_*+L₀), independently of the number of the boundary L-shell. This solution can serve as a basis for simulation of the plasmasphere formation processes, taking into account the actual conditions in the near-planetary plasma envelopes.     

The predissociation of the 2σ u −1 (c 4Σ u − , v states of the oxygen molecular ion

The dynamics of predissociation of the 2σ _u ^?1 (c ⁴Σ _u ^? ), v vibrational states of the O ₂ ⁺ ion was studied theoretically using the method of coupled differential equations. The main equations describing the vibrational motions of nuclei in the adiabatic and diabatic approximations are given. The applicability scope of approximate methods for solving these equations was studied. The predissociation widths for the v = 0 and 1 vibrational levels were found to be Γ₀ = 0.054 meV and Γ₁ = 9.71 meV. This substantiated the results of recent observations of neutral fragments formed after the dissociation of the O₂ molecule. About 99% of the O ₂ ⁺ ions in the 2σ _u ^?1 (c ⁴Σ _u ^? ), v states were found to decompose to the O(¹ D) + O⁺(⁴ S) dissociation products.     

E2 andE3 transition strengths in some rare-earth nuclei

Coulomb excitation byα-particles of vibrational-like states in even-mass rare-earth nuclei is used to determine the reduced transition probabilitiesB(E2; 0 _gs ⁺ →2 _γ ⁺ ),B(E2; 0 _gs ⁺ →2 _β ⁺ ),B(E2; 2 _gs ⁺ →0 _β ⁺ ) andB(E2; 0 _gs ⁺ →3 _oct ^? ) in¹⁵⁰Nd,^{152, 154}Sm,^{154, 158}Gd,¹⁶⁴Dy and¹⁶⁶Er. TheB(Eλ; 0 _gs ⁺ →I=λ)-values range from 2.4 to 6.5 single-particle units for transitions to the 2 _γ ⁺ -states, 0.8 single-particle units for the 2 _β ⁺ -states and from 14.1 to 21.7 single-particle units for the 3^?-states.     

Investigating the dissociation energies of niobium and vanadium oxide clusters synthesized by ion sputtering

The mass distributions and fragmentation routes of Nb _n O _m ⁺ and V _n N _m ⁺ clusters sputtered from an metal surfaces with Xe⁺ ions under O₂ pressure of P = 4?5 × 10^?3 Pa in a bombardment chamber are studied by means of secondary ion mass spectrometry. The spectra of kinetic energy release distribution (KERD) are measured for the most probable routes of the fragmentation of Nb _n O _m ⁺ and V _n N _m ⁺ and clusters, on the basis of which the activation energies of the decomposition (dissociation) of Nb _n O _m ⁺ and V _n N _m ⁺ clusters are determined within the model of evaporative ensemble and the theory of monomolecular reactions. The results show the closeness of the numerical values of dissociation energies derived using both models.     

Collision-induced dissociation of H 3 + ions

For collision energies between 100 and 500 eV the collision induced dissociation of H ₃ ⁺ colliding with H₂, He and Kr gas targets was measured. We obtained total cross sections and angular distributions of the charged collision fragments for the main reaction channels. H ₃ ⁺ +H₂→H⁺+2H² and H ₃ ⁺ +H₂→H ₂ ⁺ +H₂+H. An analysis of the kinetics yields that the dissociation proceeds via vibrational-rotational excitation of H ₃ ⁺ by mutually induced dipolmoments.