A. Tamii

Complete electric dipole response and the neutron skin in 208Pb

A benchmark experiment on (208)Pb shows that polarized proton inelastic scattering at very forward angles including 0° is a powerful tool for high-resolution studies of electric dipole (E1) and spin magnetic dipole (M1) modes in nuclei over a broad excitation energy range to test up-to-date nuclear models. The extracted E1 polarizability leads to a neutron skin thickness r(skin) = 0.156(-0.021)(+0.025) fm in (208)Pb derived within a mean-field model [Phys. Rev. C 81, 051303 (2010)], thereby constraining the symmetry energy and its density dependence relevant to the description of neutron stars.

GT strengths studied by (3He, t) reactions and nuclear matrix elements for double beta decays

Abstract GT matrix elements M S ν for transitions of 100 Mo(0 + ) → 100 Tc(1 + ) and 116 Cd(0 + ) → 116 In(1 + ) were obtained by measuring ( 3 He, t) reactions on 100 Mo and 116 Cd, respectively. The values for M S ν , together with the GT matrix elements M S ′ ν for 100 Tc(1 + ) → 100 Ru(0 + ) and 116 In(1 + ) → 116 Sn( + ), are applied to estimate the nuclear matrix elements M SS ′ 2 ν for the two neutrino double beta decays (2νββ) of 100 Mo and 116 Cd through the 1 + ground states in the intermediate nuclei of 100 Tc and 116 In, respectively. They are very close to the observed 2νββ matrix elements M 2 ν , consistent with recent experimental and theoretical analyses.

Resolving the Discrepancy of 135 MeV pd Elastic Scattering Cross Sections and Relativistic Effects

Three precise measurements for elastic pd scattering at 135 MeV/A have been performed with the three different experimental setups. The cross sections are described well by the theoretical predictions based on modern nucleon-nucleon forces combined with three-nucleon forces. Relativistic Faddeev calculations show that relativistic effects are restricted to backward angles. This result supports the two measurements recently reported by RIKEN and contradicts the KVI data.

Gamow-Teller strengths from (t,3He) charge-exchange reactions on light nuclei

Abstract Zero-degree cross sections have been measured for (t, 3 He) reactions on the light target nuclei 9 Be, 10 B, 11 B, 12 C, and 13 C at a bombarding energy of 127 MeV/A. The triton beam was produced by ( 4 He,t+p) breakup on a Be production target using a 4 He beam of 155 MeV/A. Dispersion matching was applied to obtain good energy resolution ( Δ E/E=0.002, Δ E=780 keV). The zero-degree (t, 3 He) cross sections are used to discuss Gamow-Teller strengths in 10 Be and 11 Be.

Analyzing power in elastic scattering of 6He from a polarized proton target at 71 MeV/nucleon

The vector analyzing power has been measured for the elastic scattering of neutron-rich {sup 6}He from polarized protons at 71 MeV/nucleon making use of a newly constructed solid polarized proton target operated in a low magnetic field and at high temperature. Two approaches based on local one-body potentials were applied to investigate the spin-orbit interaction between a proton and a {sup 6}He nucleus. An optical model analysis revealed that the spin-orbit potential for {sup 6}He is characterized by a shallow and long-ranged shape compared with the global systematics of stable nuclei. A semimicroscopic analysis with an {alpha}+n+n cluster folding model suggests that the interaction between a proton and the {alpha} core is essentially important in describing the p+{sup 6}He elastic scattering. The data are also compared with fully microscopic analyses using nonlocal optical potentials based on nucleon-nucleon g matrices.

Candidate Resonant Tetraneutron State Populated by the He 4 (He 8, Be 8) Reaction

A candidate resonant tetraneutron state is found in the missing-mass spectrum obtained in the double-charge-exchange reaction ^{4}He(^{8}He,^{8}Be) at 186  MeV/u. The energy of the state is 0.83±0.65(stat)±1.25(syst)  MeV above the threshold of four-neutron decay with a significance level of 4.9σ. Utilizing the large positive Q value of the (^{8}He,^{8}Be) reaction, an almost recoilless condition of the four-neutron system was achieved so as to obtain a weakly interacting four-neutron system efficiently.

Determination of the Gamow–Teller quenching factor from charge exchange reactions on 90Zr

Abstract Double differential cross sections between 0°–12° were measured for the 90 Zr(n, p) reaction at 293 MeV over a wide excitation energy range of 0–70 MeV. A multipole decomposition technique was applied to the present data as well as the previously obtained 90 Zr(p, n) data to extract the Gamow–Teller (GT) component from the continuum. The GT quenching factor Q was derived by using the obtained total GT strengths. The result is Q = 0.88 ± 0.06 , not including an overall normalization uncertainty in the GT unit cross section of 16%.

Isospin decomposition of the Gamow-Teller strength in Cu-58

Abstract The Gamow-Teller (GT) strength excited by a (p, n)-type reaction on a nucleus with isospin T0 and N > Z is shared by isospin components T0 − 1, T0 and T0 + 1. A good energy resolution (3He, t) reaction on 58Ni revealed the fine structure of the GT strength in 58Cu. The isospin of each level constituting the fine structure was assigned by comparing to results from inelastic electron and proton scatterings and (n, p)-type reactions, thus resolving the isospin structure of the GT strength in 58Cu. The ratio of the summed GT strengths among the three isospin components is well described by a shell-model calculation.

Pygmy dipole resonance in 208Pb

Scattering of protons of several hundred MeV is a promising new spectroscopic tool for the study of electric dipole strength in nuclei. A case study of 208 Pb shows that, at very forward angles, J π = 1 − states are strongly populated via Coulomb excitation. A separation from nuclear excitation of other modes is achieved by a multipole decomposition analysis of the experimental cross sections based on theoretical angular distributions calculated within the quasiparticle-phonon model. The B(E1) transition strength distribution is extracted for excitation energies up to 9 MeV; that is, in the region of the so-called pygmy dipole resonance (PDR). The Coulomb-nuclear interference shows sensitivity to the underlying structure of the E1 transitions, which allows for the first time an experimental extraction of the electromagnetic transition strength and the energy centroid of the PDR.

Analyzing power for proton elastic scattering from the neutron-rich He6 nucleus

Vector analyzing power for the proton-{sup 6}He elastic scattering at 71 MeV/nucleon has been measured for the first time, with a newly developed polarized proton solid target, which works at a low magnetic field of 0.09 T. The results are found to be incompatible with a t-matrix folding model prediction. Comparisons of the data with g-matrix folding analyses clearly show that the vector analyzing power is sensitive to the nuclear structure model used in the reaction analysis. The {alpha}-core distribution in {sup 6}He is suggested to be a possible key for understanding the nuclear structure sensitivity.