Structure of nuclei far from stability

The structure of neutron-rich unstable nuclei is discussed by focusing on three different subjects; (i) a superdeformed halo nucleus ¹¹Be studied by a deformed Woods-Saxon potential, (ii) retarded β decay due to neutron halo in ¹¹Li, and (iii) giant neutron excitations in nuclei with neutron skin.     

Masses of atomic nuclei far from stability

It is shown that a new way of applying a set of nuclear-mass relations among neighbouring nuclei, known as the Garvey–Kelson (GK) relations, holds exceptionally well for all currently measured masses. It is then demonstrated that these relationships are not adequately fulfilled for the best-known procedures to predict unknown masses. This suggests that these models may be optimized by constraining them to satisfy the (generalized) GK equations.     

Development of atomic-beam resonance method to measure the nuclear moments of unstable nuclei

We have been working on the development of a new technique of atomic-beam resonance method to measure the nuclear moments of unstable nuclei. In the present study, an ion-guiding system to be used as an atomic-beam source have been developed.     

Beta decay half lives of nuclei far from stability

Double differential cross sections for total δ-electron and K shell δ-electron emission in two angles 45° and 135° and energies 200 eV–7 keV are measured with 6 MeV p on Ar. The cross sections for K shell δ-electron emission are compared with recent calculations in PWBA with an OPM effective atomic potential⁵ and in SCA with an effective charge Coulomb potential¹².     

Properties unique in nuclei far from β stability line

Nucleons with very small binding energies present in nuclei far from the β stability line produce a unique shell structure, which leads to the disappearance of traditional magic numbers or to the creation of new magic numbers and new deformation regions. We study the shell structure in terms of the variation of two important ingredients, the kinetic energy and the spin-orbit splitting, as a function of the orbital angular momentum ℓ, when binding energies of neutrons decrease towards zero. It is also shown that for low-lying threshold strength, a negative sign is possible for the polarization charge coming from the coupling of one-particle to isoscalar shape oscillations. Received: 1 May 2001 / Accepted: 4 December 2001     

Spherical nuclei near the stability line and far from it

Results of microscopic and semiphenomenological calculations of features of spherical nuclei lying near the stability line and far from it are presented. The reason why the nuclei being considered are spherical is that they are magic at least in one nucleon sort. The present analysis is performed for Z = 50 and Z = 28 isotopes and for N = 50 isotones, the region extending from neutron-rich to neutron-deficient nuclei being covered. The isotopic dependence of the mean-field spin–orbit nuclear potential is revealed; systematics of energies of levels and probabilities for electromagnetic transitions is examined; and root-mean-square radii of nuclei are calculated, along with the proton- and neutron-density distributions in them. Nuclei in the vicinity of closed shells are considered in detail, and the axial-vector weak coupling constant in nuclei is evaluated. A systematic comparison of the results of calculations with experimental data is performed.     

Mean field and beyond in nuclei far from stability lines

We calculate, for the first time, the state-dependent pairing gap of a finite nucleus (¹²⁰Sn) diagonalizing the bare nucleon-nucleon potential (Argonne v₁₄) in a Hartree-Fock basis. The resulting gap accounts for about half of the experimental gap. Going beyond the mean field in the particle-particle channel, the combined effect of the bare nucleon-nucleon potential and of the induced pairing interaction arising from the exchange of low-lying surface vibrations between nucleons moving in time reversal states close to the Fermi energy accounts for the experimental gap. Examples for light, halo nuclei are also reported. The more studied effects of the particle-vibration coupling in the particle-hole channel are discussed for the low-lying quadrupole vibration in ¹²⁰Sn and the giant dipole resonance in the unstable oxygen isotopes and ¹³²Sn.     

Study of nuclei far from stability with the AYE-Ball array

The coupling of a Compton-suppressed Ge (CsGe) detector array to a recoil mass separator (RMS) has seen limited use in the past due to the low efficiency for measuring recoil-γ ray coincidences (< 0.1%).With the building of new generation recoil separators and gamma-ray arrays, a substantial increase in detection efficiency has been achieved. This allows for the opportunity to measure excited states in nuclei with cross-sections approaching 100 nb. In this paper, results from the coupling of a modest array of CsGe detectors (AYE-Ball) with a recoil separator (FMA) will be presented.     

Structure of nuclei far from the stability in relativistic approach

The recent progress of the relativistic many-body approach by the group at Peking University will be reviewed. In particular, axially deformed relativistic Hartree-Bogoliubov approach in Woods-Saxon basis aiming at halo nucleus, time-odd triaxial RMF approach, the adiabatic and configuration-fixed constrained triaxial RMF approaches, a Reflection ASymmetric RMF (RAS-RMF) approach, and a new relativistic Hartree-Fock (RHF) approach with density-dependent σ,ω,ρ and π meson-nucleon couplings for finite nuclei and nuclear matter, will be highlighted.     

Spectroscopy of nuclei far from stability at GANIL: Recent experiments

The structure of neutron-rich light nuclei around N = 20, 28 has been investigated at GANIL by means of in-beam gamma spectroscopy using fragmentation reactions of ³⁶S and ⁴⁸Ca beams on a Be target. Gamma decay of relatively high-lying excited states have been measured for the first time in nuclei around ³²Mg and ⁴⁴S. Level schemes are proposed and discussed for a large number of these neutron-rich nuclei around N = 20 and N = 28. Received: 1 May 2001 / Accepted: 4 December 2001     

Production of unstable nuclei far from the stability line: its scope and limitations

Recent improvements in isotope separators can be utilized along with the availability of a wide range of nuclear species from the heavy-ion fragmentation process to study hyperfine interactions. We have measured the magnetic moments of mirror nuclei using this method at the Lawrence Berkeley Laboratory's Bevalac heavy-ion accelerator. We present the merits, applicability and limitations of the technique.     

Recent developments and on-line tests of uranium carbide targets for production of nuclides far from stability

The capacity of uranium carbide target materials of different structure and density for production of neutron-rich and heavy neutron-deficient nuclides have been investigated. The yields of Cs and Fr produced by a 1 GeV proton beam of the PNPI synchrocyclotron and release properties of different targets have been measured. Yields and release efficiencies of Cs and Fr produced from a high density UC target material and from low density UCx prepared by the ISOLDE method at IRIS in the collaboration with PARRNe group from Orsay are compared. The yields from ISOLDE original target are presented for comparison as well.     

Electromagnetic moments of the doubly closed shell ±1 nucleon nuclei and on-line nuclear polarization

Electromagnetic moments of doubly closed shell ±1 nucleon nuclei were studied. Recent technical developments of the β-NMR was shown that was applicable for the polarized β emitters. Also, the implication of those new moments were discussed especially on the nuclear interactions and non nucleonic degrees of freedom.     

Iodine magnetic moments measured by on-line nuclear orientation

On-Line measurements of magnetic dipole moments of^117–122I are interpreted using coupling of the odd particles to a deformed core. The results show interesting effects of g_7/2, d_5/2 orbital admixtures in the odd-A isotopes, which are close to spherical. The odd-odd isotopes^{118, 120}I show clear examples of shape co-existence.     

Magnetic moments close to208Pb from on-line no

The nuclear magnetic moments of the shortlived isotopes^199mPo,^201mPo,²⁰¹Po and²⁰³Po have been determined with on line nuclear orientation. Together with other recently measured moments in this region, the variations with Z and N may represent a clue to an understanding of the quenching of nuclear magnetism around²⁰⁸Pb.     

Spins and level widths determined by nuclear resonance fluorescence measurements on75As

The lifetimes of the 822, 865 and 1075 keV levels in⁷⁵As, as well as the spins of the latter two levels, were determined by resonant scattering of gamma rays. The primary radiation from 3000 and 5000 Ci⁶⁰Co sources was Compton scattered to produce gamma radiation of the desired energy for photo-excitation in⁷⁵As. The lifetimes of the three levels were found to be 2.00 ps, 0.60 ps and 0.32 ps respectively. The angular distributions of the resonantly scattered radiation from the 865 keV and 1075 keV levels are consistent with spins of 5/2 and 3/2 respectively. Lifetime values are compared with excited-core model calculations.     

R-process nucleosynthesis and nuclei far from the region of β-stability

The gross theory of β-decay is applied to make improved estimates of the absolute magnitude of β-decay half-lives and related variables in the r-process calculation. The time necessary for synthesis seems to be considerably longer than assumed in some of the recent studies of the dynamic r-process. This means the necessity of suitable re-scaling of the expansion rates in the dynamics. Although the application of the improvements to the dynamics is most interesting, the present paper has limited itself to the classical quasi-static model of Seeger, Fowler and Clayton in performing the abundance calculation. The calculation method of the final abundance curve can allow several nuclear processes to interrupt β-decay cascades before the β-stability region is reached. The sudden freezing of neutron flux and temperature is assumed to precede these processes. In particular, the effect of β-delayed neutron emission after freezing is extensively studied. The β-delayed fission is also discussed. The calculated β-strength functions are compared with the recent experimental data obtained at the ISOLDE and OSIRIS facilities.     

Magnetic moments of light nuclei

Magnetic moments of the nuclei ¹⁵N, ¹⁵O, ¹⁷O, ¹⁷F and ¹⁹F are investigated. The importance ; of configuration mixing as well as meson-exchange currents is discussed in detail. Meson-exchange currents are treated in the one-boson exchange limit. Short-range N-N correlations are obtained from solutions of the Bethe-Goldstone equation for doubly closed shell nuclei by the use of realistic N-N potentials which ensure a correct treatment of tensor correlations.