Isao Tanihata

Neutron halo nuclei

Experimental studies on neutron halo nuclei are reviewed. The recent development of radioactive nuclear beams enabled us to study detailed structure of nuclei far from the stability line. The neutron halos have been observed in nuclei near the neutron dripline by reaction measurements with intermediate- and high-energy radioactive nuclear beams. These nuclei are of a special interest in relation to shell structures near the dripline and to new excitation modes associated with the excess neutron on the nuclear surface.

Electromagnetic dissociation and soft giant dipole resonance of the neutron-dripline nucleus 11Li

Abstract The electromagnetic dissociation (EMD) cross sections of light neutron-dripline projectile 11Li have been inferred from the target dependence of the interaction cross section, σ1, and the two-neutron-removal cross section, σ−2n, at an incident energy of 0.8 GeV/nucleon. The EMD cross sections of 11Li projectiles on a lead target were found to be quite large; σ I EMD ( 11 Li + Pb )=1.72 ±0.65 b and σ −2 n EMD ( 11 Li + Pb )=0.89 ±0.10 b , which are approximately 80 times larger than those of 12C projectiles after scaling the cross section by Zproj2. The large EMD cross section is related to the possible existence of a soft mode of the giant dipole resonance at low excitation energy in the extremely neutron-rich nuclei.

Neutron halo in 11Be studied via reaction cross sections

Abstract Reaction cross sections (σR) and fragmentation cross sections (σF) of reactions of a 11Be beam on C, Al targets were measured by a transmission method at 33A MeV. The σR have been determined to be 1.56±0.03 b for 11 Be + 12 C , and 2.27±0.05 b for 11 Be + 27 Al . These values are extremely large compared with the systematics of stable nuclei. A large σF has also been observed for the 11Be→10Be channel. Model calculations using present and 790A MeV data confirm the long neutron tail (neutron halo) in the 11Be density distribution.

Systematic study of Sr isotopes in the relativistic mean field theory

Abstract We study theoretically the ground state properties of the Sr isotopes with A = 78 through 100 within the relativistic mean field (RMF) theory. We make constraint calculations of the ground state energies as a function of the β deformation. We find several minima in the energy curve for each nucleus. We discuss the ground state deformation in terms of the spin of the odd mass nucleus and the quadrupole moments. In accordance with experimental observation, we can also explain the sudden increase of isotope shifts at A = 98 by a change to a configuration with large prolate deformation. Both the mass number dependence of the binding energies per particle and the charge radii are reproduced reasonably well.

Properties of nuclei far from the stability line in the relativistic hartree theory

Abstract The properties of infinite nuclear matter and spherical nuclei are studied in terms of the relativistic Hartree theory. The special emphasis is placed on the role of the rho-meson field, which provides the isovector interaction among nucleons, in determining nuclear properties far from the stability line. We find that the proton radius follows the neutron radius as the neutron number increases, by an amount which is not very sensitive to the rho-meson coupling strength. On the other hand, the neutron drip line depends largely on the rho-meson strength. Calculations with finite geometry show interesting shell effects, but the general tendency described above is unchanged.

On the Possible Use of Secondary Radioactive Beams

Since the first experiment on α scattering by Rutherford, nuclear reactions using accelerated beams of electrons, protons, deuterons, alphas, and so on, have been successfully used in the study of nuclear structure and reaction mechanisms. The use of accelerated heavy ions during the past ten years has opened a wide range of possibilities for studies in nuclear physics and other fields of research. However, until a few years ago experiments had been performed using only ions of stable isotopes.

Nuclear structure studies using high-energy radioactive nuclear beams: Radii and nucleon momentum distributions of exotic nuclei

Abstract Recent experimental results using beams of radioactive nuclei are reviewed. Radioactive beams produced through projectile fragmentations of high-energy heavy ions have been used for measurements of interaction and fragmentation cross sections. From the measured interaction cross sections, radii of unstable nuclei were deduced for light p-shell nuclei. The isospin dependence as well as the isotope dependence of the nuclear radii are discussed. The projectile fragmentation of exotic nuclei, 11 Li, have recently been observed. The existence of neutron halo in 11 Li nuclei is suggested from the data. The possibility of studying the space and the momentum distributions of nucleons in exotic nuclei are also discussed.

Strong isomer production in fragmentation reactions

Abstract The population of the 0+ 0.228 MeV isomer of 26Al has been measured in projectile fragmentation reactions at E/A = 65, 80, and 100 MeV. For beams of 27Al and 28Si, the yield of the isomer was found to be approximately equal to that of the ground state, whereas for 40Ar beams it was much weaker. The significance and utility of the surprisingly high isomer yields is discussed.

RIKEN RI beam facility and its physics programme

A construction of the radioactive ion beam facility has been started at RIKEN, which is a project to construct a four-sector ring cyclotron (IRC-4) and a six-sector superconducting ring cyclotron (SRC-6), experimental storage rings (MUSES) and an experimental facility. Heavy ions are to be accelerated to energies of up to for light nuclei and for the heaviest nuclei by the SRC-6 and up to in the MUSES. Wide varieties of radioactive nuclear beams are to be supplied as secondary beams. Electrons, stable nuclei, and highly charged ions in addition to radioactive nuclei can be stored in the storage rings. The MUSES provides various collision methods, such as colliding, merging and internal target modes. A few of the new nuclear-physics opportunities are discussed briefly.

Radioactive beam facilities and their physics program

Abstract Recently developing facilities of radioactive beams are reviewed. Both the “fragment separator type” and the “ISOL+ post accelerator type” facilities are presented. Also the progress of studies using radioactive beams are reviewed. Structure of neutron halo nuclei, formation of a thick neutron skin, elastic and inelastic scattering of unstable nuclei, and reactions relevant to stellar and primordial nucleosyntthesis are presented.