Light Unstable Nuclei Research Articles

Systematic investigation of projectile fragmentation using beams of unstable B and C isotopes

Background: Models describing nuclear fragmentation and fragmentation-fission deliver important input for planning nuclear physics experiments and future radioactive ion beam facilities. These models are usually benchmarked against data from stable beam experiments. In the future, two-step fragmentation reactions with exotic nuclei as stepping stones are a promising tool to reach the most neutron-rich nuclei, creating a need for models to describe also these reactions. Purpose: We want to extend the presently available data on fragmentation reactions towards the light exotic region on the nuclear chart. Furthermore, we want to improve the understanding of projectile fragmentation especially for unstable isotopes. Method: We have measured projectile fragments from 10,12-18C and 10-15B isotopes colliding with a carbon target. These measurements were all performed within one experiment, which gives rise to a very consistent dataset. We compare our data to model calculations. Results: One-proton removal cross sections with different final neutron numbers (1pxn) for relativistic 10,12-18C and 10-15B isotopes impinging on a carbon target. Comparing model calculations to the data, we find that EPAX is not able to describe the data satisfactorily. Using ABRABLA07 on the other hand, we find that the average excitation energy per abraded nucleon needs to be decreased from 27 MeV to 8.1 MeV. With that decrease ABRABLA07 describes the data surprisingly well. Conclusions: Extending the available data towards light unstable nuclei with a consistent set of new data have allowed for a systematic investigation of the role of the excitation energy induced in projectile fragmentation. Most striking is the apparent mass dependence of the average excitation energy per abraded nucleon. Nevertheless, this parameter, which has been related to final-state interactions, requires further study.

Unified studies of structure and reactions in light unstable nuclei

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 described in a consistent manner. GTCM is applied to the light neutron-rich system, 10,12 Be = α + α + XN (X = 2,4), and the unified studies of the structural changes and the reaction problem are performed. In the structure study, the calculated energy levels are characterized in terms of the chemical bonding like structures, such as the covalent MO or ionic VB structures. The chemical bonding structures changes from level to level within a small energy interval. In the unbound region, the structure problem with the total system of α + α + XN and the reaction problem, induced by the collision of an asymptotic VB state of α +6,8 He, are combined by GTCM. The properties of unbound resonant states are discussed in a close connection to the reaction mechanism, and some enhancement factors originated from the properties of the intrinsic states are predicted in the reaction observables. The unified calculation of the structures and the reactions is applied to the Coulomb shift problem in the mirror system, such the 10 Be and 10 C nuclei. The Coulomb displacement energy of the mirror systems are discussed.

Cluster features of stable and unstable nuclei in thep-shell region

Cluster aspects in light unstable nuclei as well as light stable nuclei are discussed. We focus on cluster structures of excited states in 12C, 9Li, and 10Be. The rotation of 3α cluster gas states in 12C and the 6He+t cluster resonances in 9Li are theoretically studied.

Cluster correlation in light nuclei

Cluster aspects in light unstable nuclei as well as light stable nuclei are discussed. The cluster structures of 13Be and 9Li were investigated. The present calculation suggests that the breaking of the neutron magicity in 13Be may occur due to the developed cluster structure as in the cases of 11Be and 12Be. Clustering in highly excited states of 9Li was discussed in conjunction with those of 10Be.

Cluster aspect of light unstable nuclei

We investigated molecular states and cluster gas-like states in light nuclei based on theoretical calculations with antisymmetrized molecular dynamics. The calculated results of 13B suggest that largely deformed states construct rotational bands, K π = 3 / 2 − and K π = 1 / 2 + , starting from 5 MeV and 8 MeV, respectively. The neutron structure of the K π = 3 / 2 − is analogous to the intruder ground state of 12Be. In the predicted K π = 1 / 2 + band, we found largely deformed structure with a proton excited configuration. The band-head 1 / 2 + state is assigned to the 1 / 2 + (4.83 MeV), which was experimentally suggested to be the proton intruder state. Structure of 8He were also investigated. In the results, it was found that the ground state of 8He has both the j- j coupling feature ( p 3 / 2 closure) and the L- S coupling feature ( 4He + 2 n + 2 n ). The results also suggest possible existence of the 0 2 + state with dineutron gas-like structure of 4He + 2 n + 2 n , which has an analogy to the 3 α-cluster structure of the 12C( 0 2 + ) state.

Light-Mass Cluster Reactions in Supernova R-Process

In explosive circumstances of the neutrino-driven winds in gravitational core-collapse Type II supernovae (SNe), not only heavy neutron-rich nuclei but also light unstable nuclei play the significant roles. We here study the efficiency and sensitivity of the SN r-process nucleosynthesis to many relevant nuclear reaction rates, and discuss quantitatively that several specific nuclear reactions on light neutron-rich nuclei take very critical keys to the final nucleosynthesis yields of r-process elements [Sasaqui, Kajino, T., T., Otsuki, K., Mathews, G. J. and Nakamura, T., Astrophys. J.(2004), submitted].

Cluster structure in stable and unstable nuclei

Cluster structure in stable and unstable nuclei has been studied. We report recent developments of theoretical studies on cluster aspect, which is essential for structure study of light unstable nuclei. We discuss negative parity bands in even-even Be and Ne isotopes and show the importance of cluster aspect. Three-body cluster structure and cluster crystallization are also introduced. It was found that the coexistence of cluster and mean-field aspect brings a variety of structures to unstable nuclei.

Ground State Properties of Beryllium Isotopes Studied by AMD + GCM Method

The ground state properties and the properties of the low-lying states of the beryllium isotopes are investigated using the extended version of the Antisymmetrized Molecular Dynamics Multi-Slater Determinant model. The theoretical method is found to be very useful to study the ground state properties of various nuclei including light unstable nuclei. Many experimental data can be successfully reproduced by the present approach. Binding energies, the energies of the 21+ states of the even-even isotopes, electromagnetic transition strengths and quadrupole moments of the proton and neutron distribution are calculated. The abnormal spin and parity of the ground state of 11Be can be described with properly chosen interaction parameters. Interesting phenomena such as the development of cluster structures is observed.

Systematic study of structure of carbon isotopes with the antisymmetrized molecular dynamics plus generator coordinate method

The structure of low-lying states of the carbon isotopes is investigated using the improved version of the Antisymmetrized Molecular Dynamics (AMD) Multi-Slater Determinant model. The theoretical method is found to be very useful to study ground-state properties of various nuclei covering light unstable nuclei. The calculations succeed to reproduce reasonably well many experimental data for the carbon isotopes 12C- 22C such as binding energies, the energies of the 2+1 states in the even-even isotopes, radii and electromagnetic transition strengths. We investigate the structure change with the increasing neutron number and observe the existence of various exotic phenomena, like the development of a neutron skin and large deformations which appear in unstable nuclei. Our calculations clearly support the existence of the N = 8 and N = 16 neutron magic numbers. The role of the spin-orbit interaction in the description of the studied isotopes and in the development of cluster structures is discussed. A special approach, important for weakly bound systems, is adopted for 15C. It enables us to better describe the tail of the wave function.

Structure of Even-Even Beryllium Isotopes Studied by AMD+GCM Method

The ground state properties and the properties of low-lying states of the even-even6Be-12Be beryllium isotopes are investigated using the extended version of the Antisymmetrized Molecular Dynamics Multi-Slater Determinant model. The theoretical method is found to be very useful to study ground state properties of various nuclei covering light unstable nuclei. Many experimental data can be successfully reproduced by the adopted approach. Binding energies, the energies of the 2 1 + states, electromagnetic transition strengths and quadrupole moments of proton and neutron distribution are calculated.

Structure of light exotic nuclei 6,8He and 10,11C from (p,p′) reactions

The structure of the light unstable nuclei 10,11C and 6,8He is investigated by means of (p,p′) reactions. The experiments were performed at GANIL using the MUST detector, an array of Si and SiLi telescopes. The (p,p′) are analyzed within the framework of the microscopic JLM potential, allowing to test the densities predicted by structure models. Preliminary data from the 8He(p,o′) reaction performed at the SPIRAL facility at 15.6 MeV/nucleon are discussed.

Cluster structures in light nuclei

Clustering in light stable and unstable nuclei is discussed. After a brief review of the clustering in stable nuclei, we make a new prediction of the existence of the alpha cluster condensed states in 12C and 16O. Discussions of clustering in light unstable nuclei are made in the cases of Be and B isotopes up to the neutron dripline.

Nuclear electromagnetic moments. [formula omitted]-NMR and its applications

Studies of magnetic moments and electric quadrupole moments for light unstable nuclei, which have been opened up by the recent development of spin-polarized radioactive nuclear beams and the β-ray detected nuclear magnetic resonance technique, are reviewed. The results lead to several intriguing findings concerning structures and interactions in unstable nuclei far from the stability line, such as a proton-halo structure in proton-rich nuclei, displacement of the single particle levels and quenching of the neutron effective charge in neutron-rich nuclei, and an anomalously large spin expectation value in a T=3/2 mirror pair. Applications of the present techniques to the study of hyperfine interactions of radioactive atoms introduced in solids are also discussed.

Structures and transitions in light unstable nuclei

We study the structures of the unstable Be isotopes with the theoretical method of antisymmetrized molecular dynamics. It is found that various structures of the excited states appear in the low-energy region of neutron-rich Be nuclei. Focusing on the 2$\alpha$ clustering, we analyze the intrinsic structures with the help of the experimental data of Gamow-Teller transitions.

Structure of Light Unstable Nuclei Studied with Antisymmetrized Molecular Dynamics

Structures of light unstable nuclei, Li, Be, B, and C isotopes are systematically studied with a microscopic method of antisymmetrized molecular dynamics. The theoretical method is found to be very useful to study ground and excited states of various nuclei covering unstable nuclei. The calculations succeed to reproduce many experimental data for nuclear structures; energies, radii, magnetic dipole moments, electric quadrupole moments, transition strength. In the theoretical results it is found that various exotic phenomena in unstable nuclei such as molecular-like structures, neutron skin, and large deformations may appear in unstabel nuclei. We investigate the structure change with the increase of neutron number and with the increase of the excitation energies, and find the drastic changes between shell-model-like structures and clustering structures. The mechanism of clustering developments in unstable nuclei are discussed.

Structure of Light Unstable Nuclei in Continuum Energies

The Coulomb breakup reaction of 6He into a 4He+n+n 3-body system is analyzed by applying the complex scaling method (CSM). We can derive the contributions to El and E2 transitions, not only from resonances, but also 2- and 3-body continuum states, which show the characteristic structure of the many-body unbound states in 6He.

Structure of excited states of10Bestudied with antisymmetrized molecular dynamics

We study structure of excited states of 10Be with the method of variation after spin parity projection in the framework of antisymmetrized molecular dynamics. Present calculations describe many excited states and reproduce the experimental data of E2 and E1 transitions and the new data of the $\beta$ transition strength successfully. We make systematic discussions on the molecule-like structures of light unstable nuclei and the important role of the valence neutrons based on the results obtained with the framework which is free from such model assumptions as the existence of inert cores and clusters.

Stochastic variational method for light unstable nuclei

We present a review of the recent application of the stochastic variational method with the correlated Gaussian basis to light unstable nuclei. It is also shown that the precise calculation of the bound-state energy can be used to determine resonance parameters by analytic continuation.

Antisymmetrized molecular dynamics plus Hartree-Fock model and its application to Be isotopes

In order to study light unstable nuclei systematically, we propose a new method, the antisymmetrized molecular dynamics plus Hartree-Fock (AMD+HF) method. This method introduces the concept of the single particle orbits into the usual AMD. Applying the AMD+HF method to Be isotopes, it is found that the calculated lowest intrinsic states with plus and minus parities have rather good correspondence with the explanation by the two-center shell model. In addition, by active use of the single particle orbits extracted from the AMD wave function, we construct the first excited ${0}^{+}$ state of ${}^{10}\mathrm{Be}.$ The obtained state appears in the vicinity of the lowest ${1}^{\ensuremath{-}}$ state. This result is consistent with the experimental data.

Quasielastic scattering of light exotic nuclei

The recent experimental data on the quasielastic scattering of light unstable nuclei on stable target nuclei are reviewed. The microscopic approaches to the construction of the nucleon density distributions in nuclei and the projectile–target interaction potentials are described. The cross sections for quasielastic scattering are analyzed for a large group of light exotic nuclei. The problem of the existence of a neutron or protonhalo in nuclei and other features of the nuclear matter distribution are discussed. Possible future experiments on quasielastic scattering and other reactions using radioactive beams are suggested.