Line-Pro le Analysis of Excitation Spectroscopy in the Even 3p5(2P1/2)nl'[K']J(l'=1,3) Autoionizing Resonances of Ar

The even-parity autoionizing resonance series 3p⁵np'[3/2]_1,2, 3p⁵np'[1/2]₁, and 3p⁵nf'[5/2]₃ of Ar have been investigated exciting from the two metastable states 3p⁵4s[3/2]₂ and 3p⁵4s'[1/2]₀ in the photon energy range of 32500-35600 cm^-1 with an experimental bandwidth of ~0.1 cm^-1. The excitation spectra of the even-parity autoionizing resonance series show typical asymmetric line shapes. New level energies, quantum defects, line profile index and resonance widths, resonance lifetime and reduced widths of the autoionizing resonances are derived by a Fano-type line-shape analysis. The line profile index q and the resonance widths Γ are shown to be approximately proportional to the effective principal quantum number n^*. The line separation of the 3p⁵np' autoionizing resonances is discussed.     

Microscopic study of Gamow-Teller and spin-dipole states in 208Bi

Gamow-Teller (GT) and spin-dipole (SD) states in ²⁰⁸Bi are studied by using self-consistent Hartree-Fock + Tamm-Dancoff approximation taking into account the coupling to the continuum. Most of SD strength is found at the excitation energy E _x≈ 25MeV with a very broad width, which agrees with recent experimental observations. It is shown that Landau damping effect is responsible for the large width of SD peak, while the escape width is found to be at most 1MeV. We study also electric dipole (E1) transitions between GT and SD states in ²⁰⁸Bi. Main E1 transitions for 0^- and 1^- states are found near excitation energy expected from Brink's hypothesis in which SD states are considered as E1 resonances built on the GT state. Calculated E1 transition strengths between GT and SD states are compared with the analytic sum rules within one-particle one-hole (1p-1h) configuration space and within both 1p-1h and 2p-2h model space. Received: 11 April 2000 / Accepted: 30 August 2000     

Microscopic analysis of the breathing mode in 40Ca and 58Ni

Recent experimental studies of the giant electric resonance region in ⁵⁸Ni and ⁴⁰Ca with inelastically scattered α-particles of energy E_α= 240 MeV are analyzed within a microscopic nuclear structure model. The model includes the continuum RPA and more complex 1p1h⊗phonon configurations. By superimposing the contributions of different multipoles up to L = 4 we obtain good agreement with the newest (reanalyzed) data for the isoscalar monopole strength and for the total (α,α′) cross section in ⁵⁸Ni. Agreement with experiment for the isoscalar monopole resonance in ⁴⁰Ca is obtained too. We emphasize the necessity of using microscopic transition densities and discuss consequences for the analyses of such experiments in light and medium mass nuclei. It is shown that the gross structure of the isoscalar monopole resonance in ⁴⁰Ca is caused by the 1p1h⊗phonon configurations. Received: 23 December 1999 / Revised version: 28 February 2000     

On the cross-over from half-metal to normal ferromagnet in NiMnSb

Magnetism and transport properties of the semi-Heusler compound NiMnSb are re-examined in great details. A wide set of experiments (elastic and inelastic neutron scattering, static magnetic measurements, magnetoresistance, Hall effect, thermopower, FMR) have been performed on polycrystals, single crystals or single-crystalline thin films, and the results are analysed. Special emphasis is given to the magnetic excitations and to the relaxation mechanisms in this metallic ferromagnet. At low temperatures, all experimental results hint at the existence of a fully spin-polarized conduction band (half metallic state). At higher temperature (T > 80 K), but well below the Curie temperature (730 K), a cross-over to a usual metallic ferromagnetic state is evidenced and discussed. Received 10 January 2000     

Pre-equilibrium dipole excitation and γ-ray fragment angular correlation in the 32S +74Ge reaction

We report on the results obtained from the study of the ³²S +⁷⁴Ge deep inelastic reaction at incident energy E= 320 MeV. High-energy γ-rays were detected in an array of 6 seven-pack BaF₂ clusters. Coincidence with complex fragments detected in 12 three-stage telescopes ensured the selection of peripheral reaction events. In order to investigate the pre-equilibrium dipole strength excitation two independent analyses were performed. In the first analysis the energy spectra of the γ-rays were evaluated in the statistical model framework while in the second one the γ-ray fragment angular correlation with respect to the nuclear spin vector of the composite system was studied. Both methods indicate the excitation of dipole strength in the highly deformed dinucleus and provide dipole resonance parameter sets that are in good agreement with each other. Received: 24 March 1999 / Revised version: 17 May 1999     

Effects of the nuclear correlations on the neutrino-oxygen interactions

We perform a calculation of the absolute charged current neutrino-oxygen events rates relevant in the atmospheric neutrino experiments. The inclusive reaction cross-section is split into exclusive channels, which are classified according to the number of Čerenkov rings they produce. The model includes the effects of residual interaction in a RPA scheme with both nucleon-hole and Delta-hole excited states and the effects of (np-nh) excitations (n=2,3). Our result is that although the flavor ratio μ/e remains almost unaffected by the nuclear effects considered here and often neglected in the Monte-Carlo simulations, the absolute events rates are subject to important modifications. Received: 15 January 1999     

Influence of the soliton in anharmonic molecular crystals with temperature on Mössbauer effect

The influence of a soliton on the properties of the M?ssbauer effect resulting from the gamma-active nuclei situated at lattice sites in quasi-one-dimensional anharmonically organic molecular chains, in which the active nuclei emit gamma-photons, has been theoretically studied by a quantum vibrational model. An expression for the gamma-radiated M?ssbauer transition probability as a function of the temperature and non-linear interaction has been obtained. Finally we give some new properties of this effect from numerical calculation in such a case, which present a way to experimentally confirm the soliton existence in molecular crystals. Received 9 April 1998 and Received in final form 11 December 1998     

Baryogenesis in the early Universe

We review various attempts to create the observed baryon asymmetry of the Universe. In particular, we consider models of GUT baryogenesis, baryogenesis via leptogenesis, the Affleck-Dine mechanism, electroweak baryogenesis and baryogenesis via topological defects and primordial black holes.     

Dimensional Resonances in Biatomic Nanostructures and the Characteristics of Their Holograms

A self-consistent problem of determining the field at the location of atoms in a nanostructural object and also at different observation points beyond a group of atoms (a small object) in the wave and near zones is solved on the basis of a system of compatible equations for the light-wave electric field strength and optical equations for linear dipole oscillators. We proved the existence of two dimensional resonances in the nanostructural object that consists of two identical atoms, with each having a single isolated resonance. We show that the properties of dimensional resonances depend strongly on small displacements of atoms with respect to one another. Formulas are obtained for effective polarizabilities of atoms in the small object. Optical plane holograms of the small object were obtained by interference of the coherent field of the dipoles of the small object and of the reference coherent wave in a certain plane of observation points far from the small object in the wave zone at frequencies corresponding to dimensional resonances.     

Evolution of the N = 20 and N = 28 shell closures in neutron-rich nuclei

The isospin dependence of shell closure phenomena is studied for light neutron-rich nuclei within a microscopic self-consistent approach using the Gogny force. Introducing configuration mixing, ³²Mg is found to be dynamically deformed, although the N = 20 spherical shell closure persists at the mean-field level for all N = 20 isotones. In contrast, the N = 28 spherical shell closure is found to disappear for N - Z≥ 10 whereas deformed shell closures are preserved and lead to shape coexistence in ⁴⁴ S. Configuration mixing shows that the ground state of this nucleus is triaxially deformed. The first 2⁺ excitation energy E_x = 1.46 MeV and the reduced transition probability B(E2;0⁺ _gs→ 2⁺ ₁)= 420 e ² fm ⁴ obtained with our approach are in good agreement with experimental data. Received: 26 July 2000 / Accepted: 30 August 2000