Core swelling in spherical nuclei: An indication of the saturation of nuclear density

Background: Nuclear radius is one of the most important and basic properties of atomic nuclei and its evolution is closely related to the saturation of the nuclear density in the internal region but the systematics of the nuclear radii for the neutron-rich unstable nuclei is not well known. Purpose: Motivated by the recent interaction cross section measurement which indicates the 48Ca core swelling in the neutron-rich Ca isotopes, we explore the mechanism of the enhancement of the neutron and proton radii for spherical nuclei. Methods: Microscopic Hartree-Fock calculations with three sets of Skyrme-type effective interactions are performed for the neutron-rich Ca, Ni and Sn isotopes. The total reaction cross sections for the Ca isotopes are evaluated with the Glauber model to compare them with the recent cross section data. Results: We obtain good agreement with the measured cross sections and charge radii. The neutron and proton radii of the various "core" configurations are extracted from the full Hartree-Fock calculation and discuss the core swelling mechanism. Conclusions: The core swelling phenomena occur depending on the properties of the occupying valence single-neutron states to minimize the energy loss that comes from the saturation of the densities in the internal region, which appears to be prominent in light nuclei such as Ca isotopes.Comment: 6 pages, 4 figures, to appear in a Rapid Communication in Phys. Rev.

Probing neutron-skin thickness with total reaction cross sections

We analyze total reaction cross sections, $\sigma_R$, for exploring their sensitivity to the neutron-skin thickness of nuclei. We cover 91 nuclei of O, Ne, Mg, Si, S, Ca, and Ni isotopes. The cross sections are calculated in the Glauber theory using the density distributions obtained with the Skyrme-Hartree-Fock method in 3-dimensional coordinate space. Defining a reaction radius, $a_R=\sqrt{\sigma_R/\pi}$, to characterize the nuclear size and target (proton or $^{12}$C) dependence, we find an empirical formula for expressing $a_R$ with the point matter radius and the skin thickness, and assess two practical ways of determining the skin thickness from proton-nucleus $\sigma_R$ values measured at different energies or from $\sigma_R$ values measured for different targets.Comment: 6 pages, 5 figures, to appear in Phys. Rev.

Interest Income and Household Savings: Evidence Based on the Maturation of Postal Savings Certificates

Japan's traditionally high household saving rate has declined substantially since the early 1990s. While this decline is often explained as a result of the rapid increase in the population share of the elderly who are dissaving, we argue that the cause is a decline in interest income triggered by falling interest rates. To examine our hypothesis, we focus on the effect of the maturation of relatively high-yielding postal savings certificates. Estimating a savings function, we find that the reduction in interest income caused by the maturation of the postal saving certificates reduced household saving rates by 3 percentage points.interest rate income, household saving rate, postal saving certificate

Did lower interest rates reduce Japan's household savings rate since the 1990s? Evidence based on the maturation of postal savings certificates

Japan's traditionally high household saving rate has declined substantially since the early 1990s. While this decline is often explained as a result of the rapid increase in the population share of the elderly who are dissaving, we argue that the cause is a decline in interest income triggered by falling interest rates. To examine our hypothesis, we focus on the effect of the maturation of relatively high-yielding postal savings certificates. Estimating a savings function, we find that the reduction in interest income caused by the maturation of the postal saving certificates reduced household saving rates by more than 3 percentage points.household savings rate

Systematic study of low-lying E1 strength using the time-dependent mean field theory

We carry out systematic investigation of electric dipole (E1) mode from light to heavy nuclei, using a new time-dependent mean field theory: the Canonical-basis Time-Dependent Hartree-Fock-Bogoliubov (Cb-TDHFB) theory. The Cb-TDHFB in the three-dimensional coordinate space representation can deal with pairing correlation and any kind of deformation in the time-dependent framework. We report the neutron-number dependence of the low-energy E1 mode for light (A 100) around N = 82.Comment: 3 pages, 2 figures, The 11th International Symposium on Origin of Matter and Evolution of Galaxies (OMEG11) proceeding

Crossover from skin-mode to proton-neutron-mode in E1E1 excitations of neutron-rich nuclei

Character of the low-energy $E1$ excitations is investigated by analyzing transition densities obtained from the RPA calculations in the doubly-magic nuclei. We propose a decomposition method of the $E1$ excitations into the $pn$ mode (i.e. oscillation between protons and neutrons) and the skin mode (oscillation of the neutron skin against the inner core) via the transition densities, by which their mixing is handled in a straightforward manner. Crossover behavior of the $E1$ excitations is found, from the skin mode at low energy to the $pn$ mode at higher energy. The ratio of the skin-mode strength to the full strength turns out to be insensitive to nuclide and to effective interactions in the energy region of the crossover. Depending on the excitation energy, the observed low-energy $E1$ excitations are not necessarily dominated by the skin mode, as exemplified for $^{90}$Zr. fied for $^{90}$Zr.Comment: 6 pages including 6 figures, to appear in PR

Systematic investigation of low-lying dipole modes using the canonical-basis time-dependent Hartree-Fock-Bogoliubov theory

Systematic investigations of the electric dipole (E1) modes of excitation are performed using the canonical-basis time-dependent Hartree-Fock-Bogoliubov (Cb-TDHFB) theory. The Cb-TDHFB is able to describe dynamical pairing correlations in excited states of nuclear systems. We apply the method to the real-time calculation of linear response in even-even nuclei with Skyrme functionals. Effects of shell structure, neutron skin, deformation, and neutron chemical potential (separation energy) are studied in a systematic way. This reveals a number of characteristic features of the low-energy E1 modes. We also find a universal behavior in the low-energy E1 modes for heavy neutron-rich isotopes, which suggests the emergence of decoupled E1 peaks beyond N = 82.Comment: 19 pages, 22 figure

Mean-field approach to superdeformed high-spin states in 40Ca and neutron-rich 50S regions

With the use of the symmetry-unrestricted cranked SHF method in the 3D coordinate-mesh representation, a systematic search for the SD and HD rotational bands in the N=Z nuclei from 32S to 48Cr has been done, and SD and HD solutions have been found in 32S, 36Ar, 40Ca, 44Ti, and in 36Ar, 40Ca, 44Ti, 48Cr, respectively. The SD band in 40Ca is found to be extremely soft against both the axially symmetric (Y30) and asymmetric (Y31) octupole deformations. Possible presense of SD states in neutron-rich sulfur isotopes from 46S to 52S has also been investigated, and deformation properties of neutron skins both in the ground and SD states are discussed.Comment: 10 pages including 9 ps figures, Talk at International Symposium on "Frontiers of Collective Motion 2002", November 6-9, 2002, Univ. of Aizu, Japa