26 research outputs found

    Level densities and γ\gamma-ray strength functions in 170,171,172^{170,171,172}Yb

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    Level densities and radiative strength functions in 171^{171}Yb and 170^{170}Yb nuclei have been measured using the 171^{171}Yb(3^3He,3^3Heγ^\prime\gamma)171^{171}Yb and 171^{171}Yb(3^3He,αγ\alpha\gamma)170^{170}Yb reactions. New data on 171^{171}Yb are compared to a previous measurement for 171^{171}Yb from the 172^{172}Yb(3^3He,αγ\alpha\gamma)171^{171}Yb reaction. Systematics of level densities and radiative strength functions in 170,171,172^{170,171,172}Yb are established. The entropy excess in 171^{171}Yb relative to the even-even nuclei 170,172^{170,172}Yb due to the unpaired neutron quasiparticle is found to be approximately 2kBk_B. Results for the radiative strength function from the two reactions lead to consistent parameters characterizing the ``pygmy'' resonances. Pygmy resonances in the 170,172^{170,172}Yb populated by the (3^3He,α\alpha) reaction appear to be split into two components for both of which a complete set of resonance parameters are obtained.Comment: 8 pages, 7 figure

    Evolution of level density step structures from 56,57-Fe to 96,97-Mo

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    Level densities have been extracted from primary gamma spectra for 56,57-Fe and 96,97-Mo nuclei using (3-He,alpha gamma) and (3-He,3-He') reactions on 57-Fe and 97-Mo targets. The level density curves reveal step structures above the pairing gap due to the breaking of nucleon Cooper pairs. The location of the step structures in energy and their shapes arise from the interplay between single-particle energies and seniority-conserving and seniority-non-conserving interactions.Comment: 9 pages, including 5 figure

    Large enhancement of radiative strength for soft transisitons in the quasicontinuum

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    Radiative strength functions (RSFs) for the 56,57-Fe nuclei below the separation energy are obtained from the 57-Fe(3-He,alpha gamma)56-Fe and 57-Fe(3-He,3-He' gamma)57-Fe reactions, respectively. An enhancement of more than a factor of ten over common theoretical models of the soft (E_gamma ~< 2 MeV) RSF for transitions in the quasicontinuum (several MeV above the yrast line) is observed. Two-step cascade intensities with soft primary transitions from the 56-Fe(n,2gamma)57-Fe reaction confirm the enhancement.Comment: 4 pages including 3 figure

    Local Density Approximation for proton-neutron pairing correlations. I. Formalism

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    In the present study we generalize the self-consistent Hartree-Fock-Bogoliubov (HFB) theory formulated in the coordinate space to the case which incorporates an arbitrary mixing between protons and neutrons in the particle-hole (p-h) and particle-particle (p-p or pairing) channels. We define the HFB density matrices, discuss their spin-isospin structure, and construct the most general energy density functional that is quadratic in local densities. The consequences of the local gauge invariance are discussed and the particular case of the Skyrme energy density functional is studied. By varying the total energy with respect to the density matrices the self-consistent one-body HFB Hamiltonian is obtained and the structure of the resulting mean fields is shown. The consequences of the time-reversal symmetry, charge invariance, and proton-neutron symmetry are summarized. The complete list of expressions required to calculate total energy is presented.Comment: 22 RevTeX page

    Level densities and γ\gamma-strength functions in 148,149^{148,149}Sm

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    The level densities and γ\gamma-strength functions of the weakly deformed 148^{148}Sm and 149^{149}Sm nuclei have been extracted. The temperature versus excitation energy curve, derived within the framework of the micro canonical ensemble, shows structures, which we associate with the break up of Cooper pairs. The nuclear heat capacity is deduced within the framework of both the micro canonical and the canonical ensemble. We observe negative heat capacity in the micro canonical ensemble whereas the canonical heat capacity exhibits an S-shape as function of temperature, both signals of a phase transition. The structures in the γ\gamma-strength functions are discussed in terms of the pygmy resonance and the scissors mode built on exited states. The samarium results are compared with data for the well deformed 161,162^{161,162}Dy, 166,167^{166,167}Er and 171,172^{171,172}Yb isotopes and with data from (n,γ\gamma)-experiments and giant dipole resonance studies.Comment: 12 figure
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