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Electron as well as proton elastic scattering is not able to determine the point proton and point neutron densities, |$\rho _\tau (r), (\tau =p,n)$|⁠ , separately. If both scatterings are analyzed consistently, those densities would be determined uniquely, since the two densities are observed by different combinations from each other. Previous experiments have not provided |$\rho _\tau (r)$| uniquely, but the values of the mean square radii of |$\rho _p(r)$|⁠ , |$\langle \, r^2\, \rangle _p$|⁠ , and of |$\rho _n(r)$|⁠ , |$\langle \, r^2\, \rangle _n$|⁠ , are shown to be determined consistently through the fourth moment of the observed charge density, |$\langle \, r^4\, \rangle _c$|⁠ , in 208Pb. The previous analyses of |$(\gamma , \pi ^0)$| and |$\bar{p}$| -nucleus obtained a similar value of |$\langle \, r^2\, \rangle _n$|⁠ , but they do not yield the experimental value of |$\langle \, r^4\, \rangle _c$| observed in electron scattering. [ABSTRACT FROM AUTHOR]

The n th moment, |$R^{(n)}_c$|⁠ , of the charge distribution is composed of not only the m (≤ n)th moments, |$R^{(m)}_p$|⁠ , of the point proton distribution, but also the m (≤ (n − 2))th ones, |$R^{(m)}_n$|⁠ , of the point neutron distribution. The experimental value of |$R^{(n)}_c(R^{(n)}_{c,{\rm exp}})$| observed through electromagnetic interaction makes it possible to investigate the point proton and neutron distributions together on the same basis. In order to estimate |$R^{(m)}_\tau (\tau =p,n)$| from |$R^{(n)}_{c,{\rm exp}}$|⁠ , however, nuclear models are required. The structure of the least-squares analysis (LSA) between |$R^{(n)}_c$| and |$R^{(m)}_\tau$| is investigated within the mean-field framework. The LSA reveals constraints inherent in the model framework through the least-squares lines (LSL) and determines the value of |$R^{(m)}_\tau$| of |$R^{(n)}_{c,{\rm exp}}$| uniquely as a result of the sum rule with respect to the coefficients of the LSL equations. The n -dependence of the values of |$R^{(m)}_\tau$| in the LSA is examined numerically by using the moments calculated up to n = 6 for 40Ca, 48Ca, and 208Pb. [ABSTRACT FROM AUTHOR]

The neutron skin thickness of asymmetric semi-infinite nuclear matter (δ R M ) is shown to be a function of the Coulomb energy (V c ), the asymmetry energy coefficient (J), the slope (L) of the asymmetry energy, and the incompressibility coefficient (K), in addition to the Fermi momentum (k F) and the asymmetry parameter (I = (N − Z)/ A). The relational formula is derived on the basis of the Hugenholtz–Van Hove theorem in the mean-field (MF) approximation for nuclear matter. Using the formula as a guide, the neutron skin thickness (δ R) in 208Pb is examined in the MF models. The apparently spurious linear correlation between L and δ R appears through the model-dependent correlation of L with J that is included in the main components of the formula. [ABSTRACT FROM AUTHOR]

It is investigated why the root-mean-square radius of the point neutron distribution is smaller by about 0.1 fm in non-relativistic mean-field models than in relativistic ones. The difference is shown to stem from the different values of the product of the effective mass and the strength of the one-body potential in the two frameworks. The values of those quantities are constrained by the Hugenholtz–Van Hove theorem. The neutron skin is not a simple function of the symmetry potential, but depends on the nucleon effective mass. [ABSTRACT FROM AUTHOR]

Physics of three-body forces in connection to exotic nuclei will be discussed. Three-nucleon forces (3NF), especially Fujita-Miyazawa 3NF, are shown to be the key for the solution to the long-standing problem of oxygen drip line, which deviates from basic trend towards the stability line. Three-body forces produce repulsive modifications to effective interaction between valence neutrons, and make the ground states less bound. The oxygen drip line is then located at the right place. The relation to the neutron matter is presented. Applications to Ca isotopes will be presented. The shell evolution due to the 3NF depicts the raising of single-particle energies and the widening of splitting among the orbits. This is in contrast to the so-called shell quenching. The 2 levels are calculated for Ca isotopes, suggesting about the same sub-magic structure for N = 32 and 34. [ABSTRACT FROM AUTHOR]

&bgr; decays of the isotones with N = 126 are studied by shell-model calculations taking into account both the Gamow-Teller (GT) and first-forbidden (FF) transitions. The FF transitions are found to be important to reduce the half-lives, by nearly twice to several times, from those by the GT contributions only. Possible implications of the short half-lives of the waiting point nuclei on the r--process nucleosynthesis during the supernova explosions are discussed. A slight shift of the third peak of the element abundances in the r process toward a higher mass region is found. [ABSTRACT FROM AUTHOR]

Structure and electromagnetic properties of exotic neutron-rich carbon isotopes are studied by shell model calculations. A p-sd shell model Hamiltonian is modified by enhancing the effects of the tensor force in the p-sd cross shell matrix elements as well as with corrections in the T=1 monopole terms. A considerable suppression of the magnetic dipole (M1) transition in 17C from the $1/2_1^ + $ state recently observed is found to be well explained by the modified Hamiltonian. The anomalous hindrance of the quadrupole (E2) transitions in 16C and 18C is also shown to be reproduced by our new Hamiltonian. [ABSTRACT FROM AUTHOR]

Abstract: Neutrino-induced reactions on 12C and 4He as well as Fe and Ni isotopes are studied, based on recent advances in shell-model calculations in p-shell and fp-shell nuclei. The charge-exchange reaction cross sections on 12C and 56Fe based on new shell-model Hamiltonians are found to be enhanced compared with previous calculations. Neutron knock-out cross sections are also found to be enhanced in 12C and 4He compared with those obtained by conventional shell-model Hamiltonians. As a consequence of this, a possible enhancement in the production yields of the light elements, 7Li and 11B, during supernova explosions is pointed out. We expect more neutrons to be knocked out by supernova neutrinos from more neutron-rich Ni isotopes. [Copyright &y& Elsevier]

We suggest that the three-body force due to the Delta-hole excitation plays a crucial role in determining the neutron drip line of oxygen isotopes. This is one of the consequences of the repulsive effective T=1 force produced by the Delta-hole excitation on the shell evolution. The same mechanism makes effective T=1 interaction more repulsive in general. [ABSTRACT FROM AUTHOR]

The relativistic expression for the |$n$| th-order moment of the nuclear charge density is presented. For the mean square radius (msr) of the nuclear charge density, the non-relativistic expression, which is equivalent to the relativistic one, is also derived consistently up to |$1/M^2$| with use of the Foldy–Wouthuysen transformation. The difference between the relativistic and non-relativistic expressions for the msr of the point proton density is also discussed. The |$n(\ge 4)$| th-order moment of the nuclear charge density depends on the point neutron density. The fourth-order moment yields useful information on the msr of the point neutron density, and is expected to play an important role in electron scattering off neutron-rich nuclei. [ABSTRACT FROM AUTHOR]

We investigated the effects of first-forbidden transitions in β decays on the production of the r -process A ∼ 195 peak. The theoretical calculated β -decay rates with β -delayed neutron emission were examined using several astrophysical conditions. As the FF decay is dominant in N ∼ 126 neutron-rich nuclei, their inclusion shortens β -decay lifetimes and shifts the abundance peak towards higher masses. Additionally, the inclusion of the β -delayed neutron emission results in a wider abundance peak, and smoothens the mass distribution by removing the odd–even mass staggering. The effects are commonly seen in the results of all adopted astrophysical models. Nevertheless there are quantitative differences, indicating that remaining uncertainty in the determination of half-lives for N = 126 nuclei is still significant in order to determine the production of the r -process peak. [ABSTRACT FROM AUTHOR]