Angular distribution of photons from the delay of the GDR in hot and rotating light Yb nuclei from exclusive experiments

Abstract Angular distributions of photons associated with the damping of excited-state giant dipole resonances (GDR) in hot and rotating 161,162 Yb nuclei have been measured in exclusive experiments using the HECTOR array. In reactions with heavy ions ( 48 T) angular distributions are determined as a function of the angular momentum of the compound nuclei. In reactions with lighter ions ( 17,18 O) a difference method is applied to isolate GDR decays originating from specific excitation regions. The systematics of the measured angular distributions as a function of excitation energy and angular momentum are compared to theories taking into account fluctuations of the shape and orientation of the excited nuclei

Excitation of low-lying states in 144Nd by means of (e,e') scattering

Abstract The low-lying states of 144Nd have been investigated up to an excitation energy of 3.1 MeV by means of high-resolution inelastic electron scattering. Transition charge densities have been extracted for natural-parity states. The experimental data have been compared with the predictions of the quasiparticle-phonon model. The calculations show that both collective and single-particle degrees of freedom are important for describing the low-lying states of 144Nd. A comparison of the present data with data for 142Nd and 142Ce emphasizes the role played by the two valence neutrons outside the N = 82 closed shell

The rotational γ-continuum in the mass region A≈110

Abstract Unresolved γ transitions of 114 Te and of 112 Sn sorted into one-dimensional and two-dimensional spectra have been studied. The reaction 64 Ni + 54 Cr at bombarding energies 230, 240, 250, 260, 270 MeV was used and the γ -rays were detected with the EUROBALL array. In the case of the nucleus 114 Te the values of the multiplicity as a function of bombarding energy and of the moment of inertia were obtained. The effective moment of inertia was found to be almost constant in the interval I=20 – 40 ℏ , in contrast to the decreasing behaviour of the dynamic moment of inertia for the terminating yrast band. The ridge valley structures in E γ 1 ×E γ 2 spectra of 114 Te and of 112 Sn were analysed with the fluctuation analysis technique. The analysis of the two nuclei are compared to simulations based on microscopic cranking calculations with residual interactions included. A rather good agreement is found between data and predictions

Low-lying states of 56 Fe

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Low-lying octupole strength in 112Cd

The low-lying octupole strength distribution in 112Cd has been measured by means of inelastic proton scattering. A splitting of the strength has been observed and interpreted as due to the interaction between the quadrupole and octupole degrees of freedom. The splitting can be reproduced by the IBA-1 model if the coupling of f- and d-bosons is considered

Quadrupole core polarization charges in the A=100 and 150 mass regions

The neutron and proton quadrupole core polarization charges are evaluated from the comparison of 0gs+ → 21+ quadrupole transition matrix elements measured by inelastic scattering of different incident probes on Mo, Pd, Cd, Nd, Sm, Gd and Dy isotopes. The resulting values, and in particular those obtained in the framework of the interacting boson model, are discussed with special attention to the evaluation of the strength of low-lying mixed-symmetry states

Effect of E1 decay in the population of superdeformed structures

Abstract Spectra of the yrast and excited superdeformed bands, forming the E2 quasi-continuum, are measured with the EUROBALL array for the nucleus 143 Eu, in coincidence with high-energy γ-rays (Eγ>3 MeV). It is found that the intensity population of the superdeformed states is enhanced by a factor of ≈1.6 when a coincidence with a γ-ray with energy >6 MeV is required, in reasonable agreement with the increase of the line shape of the Giant Dipole Resonance built on a superdeformed configuration. This result shows that when an high energy E1 γ-ray is involved in the decay it is more likely connected with a SD rather than a ND nucleus. In addition, the analysis of the rotational quasi-continuum suggests the presence of a superdeformed component. The data are also compared and found consistent with simulation calculations of the relative intensities of the SD states, including the E1 decay of superdeformed nature

Quantum tunneling of the excited rotational bands in the superdeformed nucleus 143Eu

The properties of the thermally excited rotational motion up to the region of rotational damping are studied experimentally in the superdeformed nucleus 143 Eu. The effective lifetime of the excited discrete rotational bands forming ridge structures in ‐ matrices is measured at the EUROBALL array using the DSAM technique, giving a quadrupole momentQt 10 e b, consistent with the deformation of the superdeformed yrast band. In addition, the effective number of excited superdeformed bands is extracted by a statistical analysis of the ridge structure, for transition energies down to the region where the effect of the decay-out into the normal deformed well shows up. The experimental data are compared with microscopic cranked shell model calculations including a residual interaction of surface delta type. Satisfactory agreement between data and theory is obtained when the quantum tunneling of the excited superdeformed states is included in the model. © 2001 Published by Elsevier Science B.V

Isospin character of low-lying states in 56Fe.

Low-lying states in {sup 56}Fe, up to an excitation energy of about 4 MeV, have been investigated by means of inelastic proton and deuteron scattering experiments at {ital E}{sub {ital p}}=65 and 400 MeV and at {ital E}{sub {ital d}}=56 MeV, respectively. Measured cross sections and analyzing powers have been compared with coupled-channels calculations using collective form factors; calculations in both the Schr{umlt o}dinger and Dirac formalisms have been carried out for the proton data. For each probe, the matrix elements have been deduced for transitions from the ground state and from the 2{sub 1}{sup +} state to six quadrupole (2{sup +}) states to one octupole (3{sub 1}{sup {minus}}) and two hexadecapole (4{sub 1}{sup +} and 4{sub 2}{sup +}) states. The obtained matrix elements and the previous values from {gamma} decay or electron inelastic scattering have been used to evaluate the isospin character of the transitions. To discuss the quadrupole mixed-symmetry states in {sup 56}Fe, the deduced neutron ({ital M}{sub {ital n}}) and proton ({ital M}{sub {ital p}}) components of the matrix elements, or equivalently the isoscalar ({ital M}{sub {ital s}}) and isovector ({ital M}{sub {ital v}}) parts, have been compared with theoretical calculations based on the neutron-proton interacting bosonmore » model and on the shell model evaluated in a full {ital f}-{ital p} configuration space. {copyright} {ital 1996 The American Physical Society.}« les

Microscopic model analyses of proton scattering from 12C, 20Ne, 24Mg, 28Si and 40Ca

Differential cross sections and analyzing powers for elastic scattering from, and for inelastic proton scattering to a set of $2^+_1$ states in, ${}^{12}$C, ${}^{20}$Ne, ${}^{24}$Mg, ${}^{28}$Si and ${}^{40}$Ca, and for a set of energies between 35 to 250 MeV, have been analyzed. A $g$-folding model has been used to determine optical potentials and a microscopic distorted wave approximation taken to analyze the inelastic data. The effective nucleon-nucleon interactions used to specify the optical potentials have also been used as the transition operators in the inelastic scattering processes. Shell and large space Hartree-Fock models of structure have been used to describe the nuclear states.Comment: 27 pages, 18 figure