Structure Of Light Nuclei Research Articles

ALPHA CLUSTERS IN MEDIUM LIGHT NUCLEI: RECENT RESULTS AND OPEN QUESTIONS

The presence of alpha cluster structures in light nuclei is well established. This paper concentrates on the medium light nuclei between 16 O and 44 Ti . Especially the nucleus 32 S has been examined in detail and new data is presented. The elastic scattering data of alpha particles on 28 Si forming 32 S shows a peculiar disappearance of cross section at 31 MeV excitation energy and above. Also, the energy versus J(J + 1) plot shows at least one clear rotational-like band of alpha cluster states, with the main energy levels split into many narrow and closely lying levels with the same spin. Furthermore, few experiments have been carried out investigating the alpha cluster structure of non-nα nuclei, especially on the proton rich side of stability. The evidence at hand indicates that adding neutrons retains some alpha cluster structures and in some cases might even enhance them, but adding protons seems to destroy the structures.

Structure of light nuclei in Fermionic Molecular Dynamics

Helium and Beryllium isotopes are studied in the Fermionic Molecular Dynamics model. No a priori assumptions are made with respect to cluster structure or single-particle energies. An effective interaction based on the Argonne V18 interaction is used for all nuclei. Short-range central and tensor correlations are treated explicitly using a unitary correlation operator. Mul- ticonfiguration calculations using the dipole and quadrupole moments as generator coordinates are able to describe the experimental binding energies and matter radii. The evolution of the cluster structure and the single-particle structure with increasing neutron number is discussed.

AB INITIO NUCLEAR STRUCTURE AND NUCLEAR REACTIONS IN LIGHT NUCLEI

There has been significant progress in the ab initio approaches to the structure of light nuclei. One such method is the ab initio no-core shell model (NCSM). Starting from the realistic two- and three-nucleon interactions, this method can predict the low-lying levels in p-shell nuclei. It is a challenging task to extend the ab initio methods to describe nuclear reactions. In this contribution, we present a brief overview of the NCSM with examples of recent applications as well as the first steps taken toward nuclear reaction applications.

Study of the Structure of Light Nuclei by AMD + GCM Method

The structure of stable and unstable light nuclei in the carbon region is investigated using the extended version of the Antisymmetrized Molecular Dynamics Multi-Slater Determinant model. This method has proved to be very flexible when describing structure of light nuclei where both shell model and cluster structure can appear. In this paper we address specifically the development of cluster structure in the 0 2 + state in the10Be isotope. The possibility of description of halo structure within the adopted method is discussed in the case of15C. Systematic calculations for even-even oxygen isotopes support the development of new magic numberN=16.

New Perspectives in the Studies of Resonance Scattering

We consider various possibilities for studies of nuclear structure in resonance reactions induced by radioactive beam. We discuss investigations on both sides of nuclear stability as well as studies of the a-cluster structure of light nuclei applying the reverse geometry thick target method.

Beryllium (boron) clustering quest in relativistic multifragmentation (BECQUEREL Project)

A physical program of irradiation of emulsions in beams of relativistic nuclei named the BECQUEREL Project is reviewed. It is destined to study in detail the processes of relativistic fragmentation of light radioactive and stable nuclei. The expected results would make it possible to answer some topical questions concerning the cluster structure of light nuclei. Owing to the best spatial resolution, the nuclear emulsions would enable one to obtain unique and evident results. The most important irradiations will be performed in the secondary beams of He, Be, B, C, and N radioactive nuclei formed on the basis of JINR Nuclotron beams of stable nuclei. We present results on the charged state topology of relativistic fragmentation of the 10B nucleus at low energy-momentum transfers as the first step of the research.

The structure of light nuclei and its effect on precise atomicmeasurements

The paper consists of three parts: (i) what every atomic physicist needs to know about the physics of light nuclei (and no more); (ii) what nuclear physicists can do for atomic physics; and (iii) what atomic physicists can do for nuclear physics. A brief qualitative overview of the nuclear force and calculational techniques for light nuclei will be presented, with an emphasis on debunking myths and on recent progress in the field. Nuclear quantities that affect precise atomic measurements will be discussed, together with their current theoretical and experimental status. The final topic will be a discussion of those atomic measurements that would be useful to nuclear physics. PACS No.: 31.30Gs

Compact and loosely bound structures in light nuclei

The role of various components in the wave function of loosely bound light nuclei is considered in terms of the cluster model by taking into account orbital polarization. We show that several structures corresponding to particular modes of nucleon motion can be concurrently important for such structures. Specific examples of simple and fairly flexible trial wave functions are given for the 8Be and 6He nuclei. Explicit expressions are derived for the microscopic wave functions of these nuclei and employed to calculate basic nuclear parameters for commonly used central exchange NN potentials.

Intermediate energy nuclear physics at MIT-Bates

The MIT-Bates Linear Accelerator Center is a university-based laboratory carrying out frontier research in nuclear physics. The research program is focussed on the flavor structure, charge distribution, shape, size and polarizability of the nucleon; the spin and electromagnetic structure of light nuclei; and the origin of the elements. The Bates research program has three central thrusts: the SAMPLE experiments to probe the flavor structure of the proton using parity-violating electron scattering at back angles; the OOPS (Out-Of-plane Spectrometer System) program which uses out-of-plane detection to probe nucleon and few-body nuclear structure; and the BLAST (Bates Large Acceptance Spectrometer Toroid) program which will use a new spectrometer under construction to measure electron scattering from internal gas targets in the South Hall Ring.

Structure of unstable light nuclei

The structure of light nuclei out to the drip lines and beyond up to Z∼8 is interpreted in terms of the shell model. Special emphasis is given to the underlying supermultiplet symmetry of the p-shell nuclei which form cores for neutrons and protons added in sd-shell orbits. Detailed results are given on the wave functions, widths, and Coulomb energy shifts for a wide range of non-normal parity states in the p-shell.

Spin structure of light nuclei

New data on the 1 H(3 He, ↔d) X reaction are analyzed together with the previously obtained data on (d, p), (3 He, d) and (4 He, t) momentum distributions. Polarization observables of the (d, p) reaction are also discussed. The main conclusion is that the S-wave of the 3 He→d + p vertex has no node at expected internal momenta of ≅0.4GeV/c. A similar situation is most probable for the 4 He → t + p vertex.

Structure of Light Nuclei on Neutron Drip 11The project supported financially by LWTZ-1298 of Academia Sinica and National Natural Science Foundationof China

In order to extend the conventional shell model (SM) calculation with harmonic oscillator bases to light nuclei on neutron drip line, a self-similar-structure shell model (SSM) is proposed. We do this by a rescaling of both the kinetic and potential energy terms of the harmonic oscillator so that the single-particle orbit in SSM has its own state(orbit)-dependent frequency. Meanwhile, a new method to imitate the Woods–Saxon potential with harmonic oscillator potential is introduced. By the rescaling method and imitation procedure, all light exotic nuclei together with the light stable nuclei are studied in a unified way. The results are in good agreement with experimental data. Furthermore, the puzzle of the unexistence of and is naturally explained in SSM.

Study of halo structure in light nuclei with a multicluster model

Abstract Detailed structure of light exotic nuclei is described with a multicluster model comprising α, t , 3 He, p and n clusters. The multicluster dynamics is fully taken into account with the stochastic variational method. The model enables us to describe the non-uniform and spatially extended density distribution of the halo structure. It is discussed that light stable nuclei have halo-like structure as the isospin increases.

A survey of alpha-clustering

The concept of alpha-clustering has found many applications to nuclear reactions and nuclear structure. Calculations of the properties of nuclear matter indicate that condensation into alpha-particles occurs when the density is somewhat less than the central nuclear density, suggesting that alpha clustering is favoured in the nuclear surface. This provides an explanation of alpha-decay which is now quantitatively successful. The concept of the alpha-particle mean field is now widely used to unify the alpha-particle bound and unbound states found by alpha-transfer reactions, and the scattering of alpha-particles by nuclei. The analysis of the structure of 44Ti using the alpha-40Ca potential has been particularly successful. There are now several phenomenological alpha-alpha interactions that fit the low-energy phase shifts, and these are used to calculate the structure of light nuclei, particularly those composed of 2N protons and 2N neutrons. Many excited states of such nuclei can be studied in this way, and a particularly interesting class of states is those composed of a linear chain of alpha-particles, some of which have been identified experimentally.

Production and structure of light Σ-hypernuclei

The Σ-hypernuclear bound state 4 ΣHe with J π =0 + and T∼ 1 2 (90%) is investigated on the basis of realistic ΣN interaction, with results which are in agreement with recent experimental observations. A complex nucleus-Σ potential derived has repulsion near the nuclear center in its real part, which suppresses the ΣN→ ΛN conversion decay. To get definitive information on the width and the structure of the Σ 4He, production spectra by 4He(K −, π ∓) reactions in flight at p K = 600MeV/ c are examined theoretically within the DWIA framework. The structure of light nuclei with a Σ-hyperon is also discussed.

The structure of the neutron-halo nuclei

The concept of «from core» detachment energy of valence nucleons, and the calculation of the neutron-proton interaction energy within the valence using experimental mass data, permit a very precise description of the structure of light nuclei, even of those which show a neutron halo or an anomalous electromagnetic dissociation, for instance11Be or11Li: the properties of11Be are clearly related to the negative character of the from core detachment energies \gs{in2p1} and \gs{inn3}.

β-Decay and the structure of light nuclei

An analysis of Gamow-Teller β-decay data is used to derive information on the structure of J = 1 levels in sd-shell T = 0 odd-odd nuclei within the context of an extended Interacting Boson Model (IBM-4), in particular on the relation of their orbital wavefunctions to those of levels in the neighboring T = 1 systems. The data systematically indicate that the orbital wavefunctions of the even-even ground states are generally those of levels at high excitation in the odd-odd nuclei. Predictions are made for which even-even states do have similar orbital structure to the odd-odd ground states.

β-Decay and the structure of light nuclei: R. Halse and B. R. Barrett, Physics Department, University of Arizona, Tucson, Arizona 85721

β-Decay and the structure of light nuclei: R. Halse and B. R. Barrett, Physics Department, University of Arizona, Tucson, Arizona 85721

Inclusion of the spin-orbit force in an α-cluster model

A simplified treatment is proposed to take into account the effect of the spin-orbit force within the framework of the conventional α-cluster model for light nuclei. It is very important for a study of the stability of α-cluster structure in light nuclei to include the effect of the spin-orbit force, but it has been considered that its inclusion is not so easy because (0s) 4 internal states are usually assumed for α-clusters in the model. The proposed method introduces states with [44…431] spatial symmetry by means of an operator which is just equal to a one-body spin-orbit potential. The method is applied to a 3α cluster model for 12C.

Resonances in Heavy-Ion Nuclear Reactions

The structure of light nuclei is considered from the viewpoint of molecular states. The /sup 13/C+/sup 12/C reaction is looked at in detail. (AIP)