Quasifree Neutron Knockout Reaction Reveals a Small s-Orbital Component in the Borromean Nucleus ^{17}B

Multifractal dimension spectrum analysis for nuclear density distribution

We present an integral density method for calculating the multifractal dimension spectrum for nucleon distribution in atomic nuclei. This method is then applied to analyze the non-uniformity of density distribution in several typical types of nuclear matter distributions, including the Woods-Saxon distribution, halo structure, and tetrahedral α clustering. The subsequent discussion provides a comprehensive and detailed exploration of the results obtained. The multifractal dimension spectrum shows a remarkable sensitivity to the density distribution, establishing it as a simple and novel tool for studying the distribution of nucleons in nuclear multibody systems.

Mass, Spectroscopy, and Two-Neutron Decay of ^{16}Be

The structure and decay of the most neutron-rich beryllium isotope, ^{16}Be, has been investigated following proton knockout from a high-energy ^{17}B beam. Two relatively narrow resonances were observed for the first time, with energies of 0.84(3) and 2.15(5) MeV above the two-neutron decay threshold and widths of 0.32(8) and 0.95(15) MeV, respectively. These were assigned to be the ground (J^{π}=0^{+}) and first excited (2^{+}) state, with E_{x}=1.31(6)  MeV. The mass excess of ^{16}Be was thus deduced to be 56.93(13) MeV, some 0.5 MeV more bound than the only previous measurement. Both states were observed to decay by direct two-neutron emission. Calculations incorporating the evolution of the wave function during the decay as a genuine three-body process reproduced the principal characteristics of the neutron-neutron energy spectra for both levels, indicating that the ground state exhibits a strong spatially compact dineutron component, while the 2^{+} level presents a far more diffuse neutron-neutron distribution.

Cross-Shell Excitation in F and Ne Isotopes around N = 20

Within the framework of the configuration–interaction shell model, the present work applies three effective interactions to investigate the effects of the cross-shell excitation on F and Ne isotopes around N = 20, which are significantly proton–neutron asymmetric, and have different properties compared with the proton–neutron symmetric nuclei. It is shown that cross-shell excitation is necessary in order to reproduce separation energies, neutron drip lines, and low-energy levels of these isotopes. Furthermore, the cross-shell excitation of (0–5)ħω is suggested to be important in the description of 29F and 30Ne. However, the three interactions are insufficient in describing the bound structure of 29,31Ne, and provide inconsistent shell structures and evolutions in the target nuclei. Their cross-shell interactions are suggested to be improved.

Rotating deformed halo nuclei and shape decoupling effects

To explore the rotational excitation of deformed halo nuclei, the angular momentum projection (AMP) has been implemented in the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc), in which both the mean field and collective wave functions are expanded in terms of Dirac Woods-Saxon basis. The DRHBc + AMP approach self-consistently describes the coupling between single particle bound states and the continuum not only in the ground state but also in rotational states. The rotational modes of deformed halos in ^42,44Mg are investigated by studying properties of rotational states such as the excitation energy, configuration, and density distribution. Our study demonstrates that the deformed halo structure persists from the ground state in the intrinsic frame to collective states. Especially, the typical behavior of shape decoupling effects in rotating deformed halo nuclei is revealed.