Narrow Results

Level schemes of even–even neutron-rich ^88-92Kr and ⁸⁶Se have been investigated by measuring triple-γ coincidence data from the spontaneous fission of ²⁵²Cf with the Gammasphere detector array. The level scheme of ⁸⁸Kr has been extended up to 7169 keV state. Several new excited states with new transitions have been identified in ^90,92Kr and ⁸⁶Se. Spins and parities have been assigned to levels in these nuclei by following regional systematics and angular correlation measurements. The level structures of the N = 52, 54, Se, Kr, and Sr isotones are discussed.

The high-spin states of ¹⁰⁸Ag have been studied by the in-beam γ spectroscopy with the reaction ¹⁰⁴Ru(⁷Li,3n)¹⁰⁸Ag at a beam energy of 33 MeV. The previously known positive-parity band structures have been extended up to higher spins. Their configurations are discussed based on alignments, band-crossing frequencies, and B(M1)/B(E2) ratios.

High-spin levels of ${}^{103}$Mo have been reinvestigated by analyzing the high statistics $\gamma$-$\gamma$-$\gamma$ and $\gamma$-$\gamma$-$\gamma$-$\gamma$ coincidence data from the spontaneous fission of ${}^{252}$Cf taken with the Gammasphere detector array. Two bands and 30 new transitions have been identified. A potential energy surface calculation has been performed. The calculation confirmed the 3/2${}^{+}$[411] configuration of the ground state band and 5/2${}^{-}$[532] for the 346keV excited band, as assigned in the previous work. The two newly established bands were proposed to be one- and two-phonon $\gamma$ vibrational bands coupling to the 5/2${}^{-}$[532] Nilsson orbital, respectively. Triaxial projected shell model calculations have been applied to explain the level structure and are found in good agreement with experimental data.

New transitions in neutron rich ${}^{96}$Y have been identified by analyzing the high statistics $\gamma$-$\gamma$-$\gamma$ and $\gamma$-$\gamma$-$\gamma$-$\gamma$ coincidence data from the spontaneous fission of ${}^{252}$Cf at the Gammasphere detector array. Shell model calculations were performed and are found in good agreement with experimental data. The ground state is nearly spherical but a new excited band has large deformation.

High spin structure of Zr isotopes, in particular, around $A=80$ has been studied in yrast and nonyrast regions. Spin dependence of shapes for the yrast levels are investigated by employing Cranked Hartree–Fock–Bogoliubov (CHFB) theory using a $\mathrm{\text{pairing}}+\mathrm{\text{quadrupole}}+\mathrm{\text{hexadecapole}}$ model interaction and the calculations are in good accord with the experimental data. The nonyrast states are treated by incorporating temperature degree of freedom using the statistical theory (ST). Highly deformed prolate shapes dominate the nonrotating proton rich region at low temperatures (T) with coexisting oblate and prolate shapes in ${}^{80}$Zr. Hot rotating nuclei show highest deformation around $A=80$ among all the other Zr isotopes even at high temperatures. ${}^{84}$Zr exhibits interesting structural transitions, hence studied in detail in yrast and non yrast regions. Triaxiality predominates in both yrast and nearly yrast (low temperature) regions at low spins with transition to elongated shapes at mid spin values 30–38$\hslash$ to highly deformed oblate shapes at higher spins. CHFB predicts a strong backbending effect at 32$\hslash$ and 40$\hslash$. A shape coexistence between the rare shape phase of noncollective prolate and oblate is reported in ${}^{84}$Zr at low temperature and $\mathrm{\text{spin}}=36\text{–}38\hslash$. Prolate shape phase disappears with increasing temperature and spin but the nucleus remains highly deformed (with $\beta \approx 0.4$ at spin $\ge$40$\hslash$) even at high temperatures of the order of 3–3.5MeV, hence a very promising candidate for GDR probes of nuclear shapes.

The method of description of the high-spin states, which was previously developed and applied for the states of this type in ${}^{208}$Pb, is generalized for the case of the states having more complex multiphonon structure. In this method, the harmonic approximation with the renormalized phonons is used in which the phonons themselves are determined within the nonlinear version of the model based on the random-phase approximation (RPA) and including both the RPA correlations and the beyond-RPA ones. The mean field and the residual interaction are derived within the framework of the self-consistent RPA from the energy-density functional of the Skyrme type. The method is applied for the analysis of the available experimental data in doubly magic ${}^{208}$Pb and ${}^{40}$Ca and in semi-magic ${}^{90}$Zr.

High-spin states of ¹³⁰Pr have been populated using the ⁹⁹Ru(³⁵Cl, 2n2p)¹³⁰Pr reaction at a beam energy of 151 MeV. A positive-parity side band with the same πh_11/2 ⊗ νh_11/2 configuration as that of the yrast band has been identified. The separation energy ΔE(I) between the states in the side band and the yrast band at the same spin has been studied systematically in odd-odd La and Pr isotopes. The variation trend of ΔE(I) indicates that it is reasonable to interpret the second πh_11/2 ⊗ νh_11/2 band in ¹³⁰Pr as the excited πh_11/2 ⊗νh_11/2 band as did in ¹²⁴La and ¹²⁶La, rather than to interpret it as the partner band of near degenerate chiral doublet band as did in ^128−134La and ^132−134Pr.

The high-spin states in ⁸⁹Zr have been studied by in-beam γ-ray spectroscopy using the heavy ion fusion evaporation reaction ⁷⁶Ge(¹⁹F,p5n)⁸⁹Zr reaction at a bombarding energy of 80 MeV. The level scheme of ⁸⁹Zr has been constructed up to . The large-basis shell model code OXBASH was employed to analyze the level structure of ⁸⁹Zr. The results of shell-model calculation are in good accordance with the experiment.

A new γ-ray spectroscopy method was developed using low-energy (around 5-10 MeV/u) RI beam induced fusion reaction, which enables us to study high-spin states of nuclei in wider mass region where high-spin states could not be produced by the combination of the stable beam and stable target. The low-energy ¹⁷N RI beam was produced by the direct reaction using low-energy primary beam and was transported up to the secondary target using the EN beam line at RCNP, Osaka University. Two experiments were performed to investigate the high-spin states in ¹⁴²Pr (N=83 isotone) and in ¹³⁶Ba (N=80 isotone) by this new γ-ray spectroscopy method using the low-energy ¹⁷N RI beam.

The high-spin states in the odd-A ⁸⁷Sr were populated by fusion-evaporation reaction ⁸²Se(⁹Be, 4n)⁸⁷Sr at a beam energy of 46 MeV. The positive-parity band for ⁸⁷Sr is extended up to about 7.4 MeV excitation energy and spin values around 31/2ħ in the addition of 39 new transitions. The possible condfigurations of the positive parity band are suggested by comparison with the isotope ⁸⁵Sr and the alignment value of experiment.