alpha-particle condensation in 16O studied with a full four-body orthogonality condition model calculation

New evidence of the Hoyle-like structure in 16O

An experiment of ¹²C(¹⁶O,¹⁶O → 4α)¹²C was performed at a beam energy of 96 MeV. A large number of 4-α events were recorded in coincidence and with full particle identification (PID). This was made possible by employing a series of silicon-strip-based telescopes that provided excellent position and energy resolutions. Four narrow resonances just above the 15.1 MeV state were firmly identified in the α + ¹²C(7.65 MeV; Hoyle state) decay channel. Combined with the theoretical predictions, these resonant states provide new evidence for the red predicted possible Hoyle-like structure in ¹⁶O above the 4-α separation threshold. Some very high-lying 4-α resonant states have also been observed and need to be further investigated.

The structure of 0+ states in 16O using real-time evolution method

α + 12C clustering in 16O has been vigorously studied. In the 2000s, a new picture was proposed that the Hoyle state, $^{12}{\rm{C(0}}_2^ + {\rm{)}}$, is a Bose-Einstein condensate of three α particles by the so-called THSR framework. As a next step, many researchers are interested in 4α condensate state in 16O. In this work, a microscopic calculation named the real-time evolution method (REM) was first applied to a 4α system. As a result, the 0+ states in 16O up to 4α condensate state were expected to be reproduced simultaneously for the first time.

Spin Quantization in Heavy Ion Collision

We analyzed recent experimental data on the disassembly of 28Si into 7α in terms of a hybrid α-cluster model. We calculated the probability of breaking into several α-like fragments for high l-spin values for identical and non-identical spin zero nuclei. Resonant energies were found for each l-value and compared to the data and other theoretical models. Toroidal-like structures were revealed in coordinate and momentum space when averaging over many events at high l. The transition from quantum to classical mechanics is highlighted.

Container evolution and dynamics of cluster formation

We introduce the so-called Tohsaki-Horiuchi-Schuck-Röpke (THSR) wave function to describe various nuclear cluster states. Its importance, applicability, and usefulness are extensively discussed in this report. It is demonstrated that the THSR wave function provides a “container” picture for cluster structures and even an evolution of the container, for a couple of typical examples, such as 20Ne, 12C, and 16O nuclei.

Unified studies of chemical bonding structures and resonant scattering in light neutron-excess systems, 10,12Be

The generalized two-center cluster model (GTCM), which can treat covalent, ionic and atomic configurations in general systems with two inert cores plus valence nucleons, is formulated in the basis of the microscopic cluster model. In this model, the covalent configurations constructed by the molecular orbital (MO) method and the atomic (or ionic) configuration obtained by the valence bonding (VB) method can be handled in a consistent manner. The GTCM is applied to the light neutron-rich system (10,12)Be = α + α + Xn (X = 2, 4). The continuous and smooth changes of the neutron orbits from the covalent MO states to the ionic VB states are clearly observed in the adiabatic energy surfaces (AESs), which are the energy curves obtained with a variation of the α-α distance. The energy levels obtained from the AESs nicely reproduce the recent observations over a wide energy region. The individual spectra are characterized in terms of chemical-bonding-like structures, such as the covalent MO or ionic VB structures, according to analysis of their intrinsic wave functions. From the analysis of AESs, the formation of the mysterious 0(2)(+) states in (10,12)Be, which have anomalously small excitation energies in comparison to a naive shell-model prediction, is investigated. A large enhancement in a monopole transition from a ground MO state to an ionic α + (6,8)He VB state is found, which seems to be consistent with a recent observation. In the unbound region, the structure problem, which handles the total system of α + α + Xn (X = 2, 4) as a bound or quasi-bound state, and the reaction problem, induced by the collision of an asymptotic VB state of α + (6,8)He, are combined by the GTCM. The properties of unbound resonant states are discussed in close connection to the reaction mechanism, and some enhancement factors originating from the properties of the intrinsic states are predicted in the reaction observables.

One-dimensional α condensation of α-linear-chain states in ¹²C and ¹⁶O

We present a new picture that the α-linear-chain structure for 12C and 16O has one-dimensional α condensate character. The wave functions of linear-chain states that are described by superposing a large number of Brink wave functions have extremely large overlaps of nearly 100% with single Tohsaki-Horiuchi-Schuck-Röpke wave functions, which were proposed to describe the α condensed "gaslike" states. Although this new picture is different from the conventional idea of the spatial localization of α clusters, the density distributions are shown to have localized α clusters due to the inter-α Pauli repulsion.

α-Particle clustering from expanding self-conjugate nuclei within the Hartree-Fock-Bogoliubov approach

The nuclear equation of state (EOS) is explored with the constrained Hartree-Fock-Bogoliubov approach for self-conjugate nuclei. It is found that beyond a certain low, more or less universal density, those nuclei spontaneously cluster into A/4 α particles with A the nucleon number. The energy at the threshold density increases linearly with the number of α particles as does the experimental threshold energy. Taking off the spurious c.m. energy of each α particle almost gives agreement between theory and experiment. The implications of these results with respect to α clustering and the nuclear EOS at low density are discussed.