S. Okumura

Isotopic dependence of the giant monopole resonance in the even-A Sn112-124 isotopes and the asymmetry term in nuclear incompressibility

The strength distributions of the giant monopole resonance (GMR) have been measured in the even-A Sn isotopes (A=112-124) with inelastic scattering of 400-MeV alpha particles in the angular range 0 degrees -8.5 degrees . We find that the experimentally observed GMR energies of the Sn isotopes are lower than the values predicted by theoretical calculations that reproduce the GMR energies in 208Pb and 90Zr very well. From the GMR data, a value of Ktau = -550 +/- 100 MeV is obtained for the asymmetry term in the nuclear incompressibility.

Extraction of weak transition strengths via the (He-3, t) reaction at 420 MeV

Differential cross sections for transitions of known weak strength were measured with the (3He, t) reaction at 420 MeV on targets of 12C, 13C, 18O, 26Mg, 58Ni, 60Ni, 90Zr, 118Sn, 120Sn, and 208Pb. Using these data, it is shown that the proportionalities between strengths and cross sections for this probe follow simple trends as a function of mass number. These trends can be used to confidently determine Gamow-Teller strength distributions in nuclei for which the proportionality cannot be calibrated via beta-decay strengths. Although theoretical calculations in the distorted-wave Born approximation overestimate the data, they allow one to understand the main experimental features and to predict deviations from the simple trends observed in some of the transitions.

Gamow-Teller strength for the analog transitions to the first T=1/2,J(pi)=3/2(-) states in (13)C and (13)N and the implications for type Ia supernovae

The Gamow-Teller strength for the transition from the ground state of (13)C to the T=1/2,J(pi)=3/2(-) excited state at 3.51 MeV in (13)N is extracted via the (13)C((3)He,t) reaction at 420 MeV. In contrast to results from earlier (p,n) studies on (13)C, a good agreement with shell-model calculations and the empirical unit cross-section systematics from other nuclei is found. The results are used to study the analog (13)N(e(-),nu(e))(13)C reaction, which plays a role in the pre-explosion convective phase of type Ia supernovae. Although the differences between the results from the ((3)He,t) and (p,n) data significantly affect the deduced electron-capture rate and the net heat deposition in the star resulting from this transition, the overall effect on the pre-explosive evolution is small.

Measurements of ISGMR in Sn, Cd and Pb isotopes and the asymmetry of nuclear matter incompressibility

The compression‐mode isoscalar giant monopole resonance (ISGMR) has been studied in the Sn, Cd and Pb isotopes using inelastic scattering of 400 MeV α‐particles at extreme forward angles, including 0°. We have obtained completely “background‐free” inelastic‐scattering spectra for the Sn, Cd, and Pb isotopes for a wide angular and excitation‐energy range. The various giant resonances excited with different transferred angular momenta were extracted by a multipole‐decomposition analysis (MDA). It was found that the centroid energies of the ISGMR in Sn isotopes are significantly lower than the theoretical predictions. The Kτ in the empirical expression for the nuclear incompressibility has been determined to be Kτ = −550±100 MeV for the Sn isotopes. The extracted value for the Cd isotopes is Kτ = −480±100 MeV. These numbers are consistent with values of Kτ = −370±120 MeV obtained from an analysis of the isotopic transport ratios in medium‐energy heavy‐ion reactions, Kτ = −500−100+120 MeV obtained from constr...