Molecular and cluster structures in 18O

We have studied the multi-nucleon transfer reaction ¹²C ( ⁷Li ,p) at E _lab = 44 MeV, populating states in the oxygen isotope ¹⁸O . The experiments were performed at the Tandem accelerator of the Maier-Leibniz Laboratory in Munich using the high-resolution Q3D magnetic spectrograph. States were populated up to an excitation energy of 21.2MeV with an overall energy resolution of 45keV, and 30 new states of ¹⁸O have been identified. The structure of the rotational bands observed is discussed in terms of cluster bands with the underlying cluster structures: ¹⁴C$ $\displaystyle \otimes$ $\displaystyle \alpha$ $and 12C ? 2n ? $ \alpha$ . Because of the broken intrinsic reflection symmetry in these structures the corresponding rotational bands appear as parity doublets.     

Search for Alpha Inelastic Condensed State in 24Mg

The alpha inelastic scattering from ²⁴Mg was measured to obtain the isoscalar natural-parity excitation strengths and to search for the α-condensed states. The multipole decomposition analysis for the measured cross sections was performed. The strength distributions for the ${{\Delta}L=0{-}3}$ were successfully obtained and the possible candidates for the α-condensed states around the ¹⁶O core were found.     

Gas-Like Cluster States in Finite Nuclei

Gas-like α cluster states are investigated in ¹⁶O with the use of 4α OCM (orthogonality condition model) and GEM (Gauss expansion method). α-particle condensed state is found slightly above the 4α threshold as the ${0_6^+}$ state. The candidates of the ${\alpha + {^{12}{\rm C}(0_2^+)}}$ rotational states are also found at a few megaelectron volt above the condensate. The ${0_6^+}$ state is shown to have an analogue structure to the Hoyle state ${({^{12}{\rm C}}(0_2^+))}$ and its relation with the α+ Hoyle-like rotational states is also discussed.     

States in 17O excited in the 13C + 9Be \rightarrow 13C + 2 \alpha + n reaction at 90 MeV

The ¹³C + ⁹Be reactions have been measured using a ¹³C beam with an incident energy of 90MeV. The ¹⁷O excitation energy spectra have been reconstructed from the detected ¹³C + $ \alpha$ coincidences. A number of the ¹⁷O states has been observed and their structure has been discussed in relation to the well-known ¹⁶O cluster states.     

Extreme \alpha -clustering in the 18O nucleus

The structure of the ¹⁸O nucleus at excitation energies above the $ \alpha$ decay threshold was studied using ¹⁴C + $ \alpha$ resonance elastic scattering. A number of states with large $ \alpha$ reduced widths have been observed, indicating that the $ \alpha$ -cluster degree of freedom plays an important role in this N $ \ne$ Z nucleus. A 0⁺ state with an $ \alpha$ reduced width exceeding the single-particle limit was identified at an excitation energy of 9.9±0.3 MeV. We discuss evidence that states of this kind are common in light nuclei and give possible explanations of this feature.     

The N = 16 Spherical Shell Closure in 24O

The unbound excited states of the most neutron-rich dripline oxygen isotope, ²⁴O, have been investigated by using the ²⁴O(p,p′)²⁴O^* reaction at the beam energy of 62 MeV/nucleon in inverse kinematics. The first and second unbound excited states of ²⁴O have been observed at ${E_{\rm x}= 4.63_{-0.14}^{+0.30}}$  MeV and ${E_{\rm x}= 5.13_{-0.24}^{+0.19}}$  MeV (preliminary) along with the evidence for another higher lying state at around 7.3 MeV. The quadrupole deformation parameter ${\beta_{2^+}}$ was deduced to be ${0.15_{-0.03}^{+0.08}}$ (preliminary) for the first time. The systematics of the ${\beta_{2^+}}$ and the ${E_{\rm x}(2_1^+)}$ in the Z = 8 isotopes shows the N = 16 spherical shell closure in ²⁴O.     

Resonance States and Alpha Condensation in 12C and 16O

Low density states near the 3α and 4α breakup thresholds in ¹²C and ¹⁶O, respectively, are discussed in terms of the α-particle condensation. Calculations are performed in Orthogonality Condition Model and Tohsaki–Horiuchi–Schuck–Röpke approaches. The ${0_2^+}$ state in ¹²C and the ${0_6^+}$ state in ¹⁶O are shown to have dilute density structures and give strong enhancement of the occupation of the S-state c.o.m. orbital of the α-particles. The possibility of the existence of α-particle condensed states in heavier nα nuclei is also discussed.     

2α + t Cluster Structure in 11B

Structures of excited states in ¹¹B are investigated with a method of β – γ constraint antisymmetrized molecular dynamics in combination with the generator coordinate method. Various cluster structures are suggested in excited states. For negative-parity states, we suggest a band with a 2α + t cluster structure. This band starts from the ${3/2^{-}_{3}}$ state and can correspond to the experimental band observed recently. We find that the feature of the ${3/2^{-}_{3}}$ is quite similar to the ${0^{+}_{2}}$ state in ¹²C.     

Effective chiral symmetry restoration in excited mesons

Results on the spectrum of ${\bar q} q$ mesons in a model with a linear Coulomb-like instantaneous confining potential are presented. The single-quark Green function as well as the dynamical chiral symmetry breaking are obtained from the Dyson-Schwinger (gap) equation. Given the dressed quark propagator, the spectrum of “usual” mesons, i.e., ${\bar q} q$ states with nonexotic quantum numbers J ^PC , is obtained from the Bethe-Salpeter equation. Effective restoration of chiral symmetry at large spins and/or radial excitations is observed and the states fall into approximate linear radial and angular Regge trajectories.     

Spectroscopy of88Y homologous levels

The⁹¹Zr( $z\bar p$ ,α)⁸⁸Y reaction has been studied at incident energy of 22 MeV using a polarized proton source and a Q3D spectrometer. The differential cross sections and asymmetries for transitions to levels of⁸⁸Y homologous to the lowest excitation energy states of⁸⁷Y have been measured and interpreted both in terms of the experimental differential cross sections and asymmetries of the parent⁸⁷Y states and by means of the finite-range distorted wave Born approximation theory using conventional Woods-Saxonα-particle potential. The advantage of the concept of homology consists in having to deal with a uniquel-transfer, that given by the transition to the corresponding parent state. In order to validate the concept of homology as a spectroscopic tool to identify spin, parity and dominant configuration of highly excited states in ( $z\bar p$ ,α) reaction on odd mass target nuclei, shell model calculations have been performed. Several new attributions of spin and parity for⁸⁸Y residual nucleus are proposed.     

Skyrme-QRPA calculations for low-lying excitation modes in deformed neutron-rich nuclei

Low-frequency modes of excitation in deformed neutron-rich nuclei are studied by means of the quasiparticle random-phase approximation on the Skyrme-Hartree-Fock-Bogoliubov mean field. We investigate the microscopic structure of the soft $\ensuremath K^{\pi} = 0^{+}$ modes systematically in neutron-rich magnesium isotopes with N = 22, 24, 26 and 28 close to the drip line, and it is found that the strong collectivity in ³⁴Mg and ⁴⁰Mg is acquired due to the coherent coupling between the $ \beta$ vibration and the pairing vibration of neutrons. Microscopic structure of the $\ensuremath K^{\pi} = 2^{+}$ modes changes gradually associated with the location of the Fermi level of neutrons, and it is found that the proton particle-hole excitation generating the $ \gamma$ -vibrational mode in ²⁴Mg continues to play a key role in the near-drip-line nucleus ⁴⁰Mg . The low-frequency octupole excitations are also investigated and the microscopic mechanism for the enhancement of transition strengths is discussed.     

Baryon resonances as hadronic molecule states with kaons

We investigate hadronic molecule states of $K \bar K N$ and $\bar K \bar K N$ systems with I?=?1/2 and J ^P ?=?1/2^?+?, assuming that Λ(1405) and the scalar mesons, f ₀(980), a ₀(980), are reproduced as quasi-bound states of $\bar KN$ and $K \bar K$ . Performing non-relativistic three-body calculations for these systems, we find weakly bound states for $K \bar K N$ and $\bar K \bar K N$ around 1900 MeV, which correspond to new baryon resonances of N ^* and Ξ ^* with J ^P ?=?1/2^?+?. We find that these resonances have cluster structure of the two-body bound state keeping its properties as in the isolated two-particle system.     

Yrast spectroscopy in 49-51Ti via fusion-evaporation reaction induced by a radioactive beam

In-beam $ \gamma$ -ray spectroscopy of high-spin states in ^49-51Ti was performed via the fusion-evaporation reaction using a radioactive beam. By excitation function and $ \gamma$ - $ \gamma$ coincidence analysis, yrast high-spin levels up to I = (21/2^-),(11⁺),(17/2^-) in ^49-51Ti were determined. The levels were compared with full-pf -shell model calculation. The level structure indicates the persistency of the N = 28 shell gap at yrast states in ^49-51Ti .     

Domain wall theory of elementary excitations in anisotropic antiferromagneticS=1 chains

We present a theoretical investigation of elementary excitations in anisotropic antiferromagneticS=1 chains using the concept of domain walls in string (hidden) order. Domain walls are classified by the internal spin projectionS _dw ^z . We calculate energies and string correlation functions of low lying excited states of the domain wall type in the Haldane phase and compare the results to those of numerical computations. The boundaries of the Haldane phase are determined from the instability of these excitations with respect to the ground state. The interaction between two domain walls is found to be proportional to the productS _dw ^z , S _dw ^z ₂, it is effectively repulsive for equal spin projections.     

Description of high-spin isomers in theN=82 region

The high spin states and of those especially the yrast isomers are studied in the region near the rare earth nuclei. The deformation energy surface is calculated with a method modelled in principle according to a shape constrained cranked HF theory (CHF). In practice, the expectation value of the many-body Hamiltonian is calculated with cranked Nilsson functions. One finds rotation around a slightly deformed oblate or prolate symmetry axis in front or behind the rare earth region, respectively. Near the Hf isotopes strongly prolate deformed nuclei rotating around the symmetry axis are found in agreement with the knownK isomers in this region. These results are explained also qualitatively with the help of the MONA (Maximisation of theOverlap ofNucleonic wave functions byAlignment of single particle angular momenta) effect. In the second part high spin states and yrast isomers in theN=82 region are caluclated in the cranked Hartree-Fock-Bogoliubov approach with four and six quasi-particle excitations. For the excitation energies in¹⁴⁶Gd and¹⁵²Dy and a measuredg factor one finds satisfactory agreement.     

Description of high-spin isomers in theN=82 region

The high spin states and of those especially the yrast isomers are studied in the region near the rare earth nuclei. The deformation energy surface is calculated with a method modelled in principle according to a shape constrained cranked HF theory (CHF). In practice, the expectation value of the many-body Hamiltonian is calculated with cranked Nilsson functions. One finds rotation around a slightly deformed oblate or prolate symmetry axis in front or behind the rare earth region, respectively. Near the Hf isotopes strongly prolate deformed nuclei rotating around the symmetry axis are found in agreement with the knownK isomers in this region. These results are explained also qualitatively with the help of the MONA (Maximisation of theOverlap ofNucleonic wave functions byAlignment of single particle angular momenta) effect. In the second part high spin states and yrast isomers in theN=82 region are calculated in the cranked Hartree-Fock-Bogoliubov approach with four and six quasi-particle excitations. For the excitation energies in¹⁴⁶Gd and¹⁵²Dy and a measuredg factor one finds satisfactory agreement.     

Level structures in the 114 In nucleus

High-spin states in ¹¹⁴In were populated using the reaction ¹¹⁰Pd(⁷Li, 3n)¹¹⁴In at a beam energy of 26MeV. The level scheme of ¹¹⁴In consisting of six bands is established up to excitation energy ～ 5MeV and spin ～ 17 ? with the addition of 58 new transitions and their configurations are discussed. The intense positive-parity dipole cascade may be interpreted as shears band based on $ \pi$ [(g _9/2)^-1] ? $ \nu$ [(g _7/2/d _5/2)(h _11/2)²] configuration. The $ \Delta$ I = 2 bands based on proton excitation have been observed in ¹¹⁴In for the first time.     

Isomerism of low-lying states in 86Y

Low-energy isomeric states of ⁸⁶Y were populated in the reaction ⁷³Ge + ¹⁶O at 57MeV and were investigated by means of delayed n $ \gamma$ and $ \gamma$ $ \gamma$ coincidences. A half-life of 70(7)ns was measured for the 5^- state at 208keV, yielding an exceptionally small B(M1) value of 2.0(7)×10^-5 W.u. and a B(E2) value of 0.34(⁺²⁴ _-13) W.u. For the other three known isomeric states at 218, 243, and 302keV, the half-lives extracted from the present experimental data are in very good agreement with previous measurements. Given the newly observed isomeric character of the 5^- 208keV state, the re-analysis of earlier experimental data on the 302keV isomer led to a new spin-parity assignment, 6⁺, for this state. In addition, this re-evaluation provided two g -factors, -0.083(3) and +0.63(2) , for the 208 and 302keV states, respectively. The results are discussed in terms of spherical-shell model calculations performed with a truncated space of configurations built on the f _5/2 , p _3/2 , p _1/2 , and g _9/2 valence orbitals. Effective spin, orbital, and “tensor” g -factors were determined empirically for protons and neutrons in the considered configuration space.