H. Toki

An effective interaction for inelastic scattering derived from the Paris potential

An effective interaction for inelastic scattering of nucleons from nuclei is derived by fitting oscillator G-matrix elements of the Paris nucleon-nucleon potential to the matrix elements of a sum of Yukawa terms. Except for the singlet-odd channel, these G-matrix elements do not differ in any significant respect from those obtained from the Reid soft-core potential, and give similar results for inelastic proton scattering.

Liquid-gas phase instabilities in nuclear systems☆

Abstract The conventional approach to composite fragment production in heavy ion collisions from a single gaseous phase may require modification at temperatures below 20 MeV due to the onset of a liquid-gas phase instability. Clusters heavier than the α-particle are necessary for an unambigous experimental signature.

Quenching of magnetic transitions and Δ(1232) degrees of freedom in nuclei: the 48Ca case☆

Abstract The quenching of M1 transitions is discussed within the framework of an effective magnetic transition operator renormalized by virtual Δ(1232)-hole excitations. This scheme is applied to the M1 transition from the ground state to the 10.23 MeV (1 + ) state in 48 Ca, a case which appears to reveal a comparatively simple shell-model structure. It is demonstrated that a large fraction of the observed quenching of the B (M1) value can be related to Δ(1232) degrees of freedom in a way consistent with the quenching of Gamow-Teller transitions.

Double-Δ (1232) formation in pion-nucleus absorption

Abstract Double- Δ (1232) formation following pion absorption in and above the 3.3 resonance region is shown to provide an important absorption mechanism for heavy nuclei, if the Δ N → ΔΔ interaction behaves according to SU (4) quark model rules. The ΔΔ configuration is formed preferentially in T = 2 states and decays predominantly by emission of four nucleons, unlike the standard π NN → Δ N → NN two-nucleon process. We show that this mechanism is able to explain some of the striking features observed in proton emission spectra following π ± -nucleus absorption in the Δ region.

Chiral bag plus skyrmion hybrid model for nucleons

Abstract The chiral bag plus skyrmion hybrid model is studied as a model for nucleons. The hybrid model is solved numerically, where great care has been taken to remove the divergence in the boundary condition at the chiral bag surface for the nonlinear differential equation of the skyrmion. The numerical results for the nucleon energy turn out to be finite for all bag radii, differing from the case of the linearized chiral model. With a suitable choice of the bag parameter (volume term), the nucleon mass, radius and the axial vector coupling constant g A come out to be very promising.

New cascade model calculation of pion multiplicity in high-energy heavy-ion collisions☆

Abstract Pion multiplicities in nuclear collisions are calculated using the nuclear cascade model developed by Kitazoe et al. This cascade model differs in particular from previous models in the way binding, Pauli principle, and Fermi motion effects are treated. The treatment of such details in the cascade is found to have significant influence on the pion multiplicities. Close agreement with the Ar + KCl central collision data is obtained without introducing the compressional energy effect postulated by Stock et al.

Beta decay rates of sd-shell nuclei in stellar interiors

Abstract Gamow-Teller matrix elements of sd-shell nuclei relevant for stellar evolution of massive stars are calculated by using the sd-shell model wave functions of Wildenthal. Emphasis is placed on the calculations of GT transitions between excited states, which are not obtainable by experiment. Our results are compared with the previous work by Fuller et al. and are found notably different in many cases. The beta decay rates, as calculated with and without the contributions of excited states, are demonstrated to be quite different under conditions of high density and high temperature.

Baryon spectra in the interacting boson model

Abstract We propose the interacting boson model (IBM) description of the excitation spectra built on N(1440), Δ (1600) and Λ (1600). The adopted SU(3) symmetry suggests that the positive parity excited states of the baryons (N, Δ and Λ ) are realized as deformed objects.

Isospin dependence of pion absorption by nucleon pairs in the He isotopes

Abstract We calculate the relative absorption ratio of a pion by T = 0 and T = 1 nucleon pairs in the He isotopes measured recently by Ashery et al. Standard theory based on Δ-isobar intermediate excitations agrees with the experimental observation that for energies around the resonance, pion absorption by a T = 1 nucleon pair is strongly suppressed.

Quenched magnetic transitions from high spin states in light nuclei

Recent investigations of stretchedM 6 transitions in thes-d shell have uncovered the unexpected systematic trend that isoscalarM 6 transitions are two to three times more retarded than the isovector ones. We present the result of a microscopic calculation analyzing the different mechanisms usually invoked in the formation of the quenching and suggest that an additional argument based on the difference in structure between isoscalar and isovector transition densities may be playing a predominant role in explaining the data.