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Register a new user$^{16}$O + $^{16}$O molecular structures of positive- and negative-parity superdeformed bands in $^{34}$S
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Yasutaka Taniguchi
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The structures of excited states in $^{34}$S are investigated using the antisymmetrized molecular dynamics and generator coordinate method (GCM). The GCM basis wave functions are calculated via energy variation with a constraint on the quadrupole deformation parameter $beta$. By applying the GCM after parity and angular momentum projections, the coexistence of two positive- and one negative-parity superdeformed (SD) bands are predicted, and low-lying states and other deformed bands are obtained. The SD bands have structures of $^{16}$O + $^{16}$O + two valence neutrons in molecular orbitals around the two $^{16}$O cores in a cluster picture. The configurations of the two valence neutrons are $delta^2$ and $pi^2$ for the positive-parity SD bands and $pi^1delta^1$ for the negative-parity SD band. The structural changes of the yrast states are also discussed.
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An inelastic excitation and cluster-decay experiment $rm {^2H}(^{16}C,~{^{4}He}+{^{12}Be}~or~{^{6}He}+{^{10}Be}){^2H}$ was carried out to investigate the linear-chain clustering structure in neutron-rich $rm {^{16}C}$. For the first time, decay-paths from the $rm {^{16}C}$ resonances to various states of the final nuclei were determined, thanks to the well-resolved $Q$-value spectra obtained from the three-fold coincident measurement. The close-threshold resonance at 16.5 MeV is assigned as the ${J^pi}={0^+}$ band head of the predicted positive-parity linear-chain molecular band with ${(3/2_pi^-)^2}{(1/2_sigma^-)^2}$ configuration, according to the associated angular correlation and decay analysis. Other members of this band were found at 17.3, 19.4, and 21.6 MeV based on their selective decay properties, being consistent with the theoretical predictions. Another intriguing high-lying state was observed at 27.2 MeV which decays almost exclusively to $rm {^{6}He}+{^{10}Be{(sim6~ MeV)}}$ final channel, corresponding well to another predicted linear-chain structure with the pure $sigma$-bond configuration.
Collisions of light and heavy nuclei in relativistic heavy-ion collisions have been shown to be sensitive to nuclear structure. With a proposed $^{16}mathrm{O}^{16}mathrm{O}$ run at the LHC and RHIC we study the potential for finding $alpha$ clustering in $^{16}$O. Here we use the state-of-the-art iEBE-VISHNU package with $^{16}$O nucleonic configurations from {rm ab initio} nuclear lattice simulations. This setup was tuned using a Bayesian analysis on pPb and PbPb systems. We find that the $^{16}mathrm{O}^{16}mathrm{O}$ system always begins far from equilibrium and that at LHC and RHIC it approaches the regime of hydrodynamic applicability only at very late times. Finally, by taking ratios of flow harmonics we are able to find measurable differences between $alpha$-clustering, nucleonic, and subnucleonic degrees of freedom in the initial state.
We report converged results for the ground and excited states and matter density of 16-O using realistic two-body nucleon-nucleon interactions and coupled-cluster methods and formalism developed in quantum chemistry. Most of the binding is obtained with the coupled-cluster singles and doubles approach. Additional binding due to three-body clusters (triples) is minimal. The coupled-cluster method with singles and doubles provides a good description of the matter density, charge radius, charge form factor, and excited states of a 1-particle-1-hole nature, but it cannot describe the first excited 0+ state. Incorporation of triples has no effect on the latter finding.
We investigate the linear-chain configurations of four-$alpha$ clusters in $^{16}$O using a Skyrme cranked Hartree-Fock method and discuss the relationship between the stability of such states and angular momentum. We show the existence of a region of angular momentum (13-18 $hbar$) where the linear chain configuration is stabilized. For the first time we demonstrate that stable exotic states with a large moment of inertia ($hbar^2/2Theta$ $sim$ 0.06-0.08 MeV) can exist.
The elastic scattering angular distribution of the $^{16}$O$+^{60}$Ni system at $260$ MeV was measured in the range of the Rutherford cross section down to $7$ orders of magnitude below. The cross sections of the lowest $2^{+}$ and $3^{-}$ inelastic states of the target were also measured over a several orders of magnitude range. Coupled channel (CC) calculations were performed and are shown to be compatible with the whole set of data only when including the excitation of the projectile and when the deformations of the imaginary part of the nuclear optical potential are taken into account. Similar results were obtained when the procedure is applied to the existing data on $^{16}$O$+^{27}$Al elastic and inelastic scattering at $100$ and $280$ MeV. An analysis in terms of Dynamical Polarization Potentials (DPP) indicate the major role of coupled channel effects in the overlapping surface region of the colliding nuclei.
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