Y. Shimizu

Excitation spectra of two impurity Anderson model

Abstract Magnetic and single particle excitation spectra of the two impurity Anderson model are calculated based on the numerical renormalization method. The direct f-f hoping or the realistic c-f hybridization terms cause the splitted Kondo peaks corresponding to the even and odd parity channels. The antiferromagnetic fluctuation of local spin pair shows softening when it has weak antiferromagnetic coupling. This softening, and the divergence of the staggered susceptibility previously pointed out by Jones et al. are suppressed by the parity splitting.

Nucleus

The unbound nucleus ^{26}O has been investigated using invariant-mass spectroscopy following one-proton removal reaction from a ^{27}F beam at 201u2009u2009MeV/nucleon. The decay products, ^{24}O and two neutrons, were detected in coincidence using the newly commissioned SAMURAI spectrometer at the RIKEN Radioactive Isotope Beam Factory. The ^{26}O ground-state resonance was found to lie only 18±3(stat)±4(syst)u2009u2009keV above threshold. In addition, a higher lying level, which is most likely the first 2^{+} state, was observed for the first time at 1.28_{-0.08}^{+0.11}u2009u2009MeV above threshold. Comparison with theoretical predictions suggests that three-nucleon forces, pf-shell intruder configurations, and the continuum are key elements to understanding the structure of the most neutron-rich oxygen isotopes beyond the drip line.

^{26}

The electric dipole strength distribution in 120Sn between 5 and 22 MeV has been determined at RCNP Osaka from a polarization transfer analysis of proton inelastic scattering at E_0 = 295 MeV and forward angles including 0{deg}. Combined with photoabsorption data an electric dipole polarizability alpha_D(120Sn) = 8.93(36) fm^3 is extracted. The dipole polarizability as isovector observable par excellence carries direct information on the nuclear symmetry energy and its density dependence. The correlation of the new value with the well established alpha_D(208Pb) serves as a test of its prediction by nuclear energy density functionals (EDFs). Models based on modern Skyrme interactions describe the data fairly well while most calculations based on relativistic Hamiltonians cannot.

O : A Barely Unbound System beyond the Drip Line

Electric dipole strength in 120 Sn below the neutron threshold has been extracted from proton inelastic scattering experiments at Ep = 295 MeV and at forward angles including 0 . The strength distribution is very dierent from the results of a 120 Sn(; 0 ) experiment and peaks at an excitation energy of 8.3 MeV. The total strength corresponds to 2.3(2)% of the energy-weighted sum rule and is more than three times larger than what is observed with the (; 0 ) reaction. This implies a strong fragmentation of the E1 strength and/or small ground state branching ratios of the excited 1 states.

Dipole polarizability of 120 Sn and nuclear energy density functionals

SAMURAI project aims to open a new research field in nuclear physics by the use of a large acceptance spectrometer for kinematically complete measurements of multiple particles emitted in RI-beam induced reactions. The SAMURAI spectrometer consists of a large gap superconducting dipole magnet, heavy ion detectors, neutron detectors, and proton detectors. What is special about the SAMURAI system is that projectile-rapidity protons or neutrons are detected with large angular and momentum acceptance in coincidence with heavy projectile fragments. With an effective combination of these equipments, the SAMURAI system allows us to perform various experiments: electromagnetic dissociation, various direct reactions, polarized deuteron induced reactions, and EOS studies. SAMURAI project is currently underway at RIBF. The construction of the superconducting dipole magnet will start in autumn 2010 and finish in spring 2011. The detectors are also being constructed in parallel. The first commissioning run will be performed in early 2012.

Low-energy electric dipole response in 120Sn

We demonstrate frequency offset locking between two laser sources using a waveguide-type electro-optic modulator (EOM) with 10th-order sidebands for magneto-optical trapping of Fr atoms. The frequency locking error signal was successfully obtained by performing delayed self-homodyne detection of the beat signal between the repumping frequency and the 10th-order sideband component of the trapping light. Sweeping the trapping-light and repumping-light frequencies with keeping its frequency difference of 46 GHz was confirmed over 1 GHz by monitoring the Doppler absorption profile of I₂. This technique enables us to search for a resonance frequency of magneto-optical trapping of Fr.

SAMURAI Project at RIBF

We study for the first time the internal structure of 140Te through the beta-delayed gamma-ray spectroscopy of 140Sb. The very neutron-rich 140Sb, Z = 51 and N = 89, ions were produced by the in-flight fission of 238U beam on a 9Be target at 345 MeV per nucleon at the Radioactive Ion Beam Factory, RIKEN. The half-life and spin-parity of 140Sb are reported as 124(30) ms and (4-), respectively. In addition to the excited states of 140Te produced by the beta-decay branch, the beta-delayed one-neutron and two-neutron emission branches were also established. By identifying the first 2+ and 4+ excited states of 140Te, we found that Te isotopes persist their vibrator character with E(4+)/E(2+) = 2. We discuss the distinctive features manifest in this region, such as valence neutron symmetry and asymmetry, revealed in pairs of isotopes with the same neutron holes and particles with respect to N = 82.

Laser frequency locking with 46 GHz offset using an electro-optic modulator for magneto-optical trapping of francium atoms.

Several new isotopes, ^{96}In, ^{94}Cd, ^{92}Ag, and ^{90}Pd, have been identified at the RIKEN Nishina Center. The study of proton drip-line nuclei in the vicinity of ^{100}Sn led to the discovery of new proton emitters ^{93}Ag and ^{89}Rh with half-lives in the submicrosecond range. The systematics of the half-lives of odd-Z nuclei with T_{z}=-1/2 toward ^{99}Sn shows a stabilizing effect of the Z=50 shell closure. Production cross sections for nuclei in the vicinity of ^{100}Sn measured at different energies and target thicknesses were compared to the cross sections calculated by epax taking into account contributions of secondary reactions in the primary target.

Nuclear structure and β -decay schemes for Te nuclides beyond N=82

The low-lying unbound level structure of the halo nucleus 19 C has been investigated using single-neutron knockout from 20 C on a carbon target at 280 MeV/nucleon. The invariant mass spectrum, derived from the momenta of the forward going beam velocity 18 C fragment and neutrons, was found to be dominated by a very narrow near threshold ( Erel=0.036(1) MeV) peak. Two less strongly populated resonance-like features were also observed at Erel=0.84(4)xa0andxa02.31(3) MeV, both of which exhibit characteristics consistent with neutron p -shell hole states. Comparisons of the energies, measured cross sections and parallel momentum distributions to the results of shell-model and eikonal reaction calculations lead to spin-parity assignments of 5/21+ and 1/21− for the levels at Ex=0.62(9)xa0andxa02.89(10) MeV with Sn=0.58(9) MeV. Spectroscopic factors were also deduced and found to be in reasonable accord with shell-model calculations. The valence neutron configuration of the 20 C ground state is thus seen to include, in addition to the known 1s1/22 component, a significant 0d5/22 contribution. The level scheme of 19 C, including significantly the 1/21− cross-shell state, is well accounted for by the YSOX shell-model interaction developed from the monopole-based universal interaction.

New Isotopes and Proton Emitters Crossing the Drip Line in the Vicinity of

In this Letter, the observation of two previously unknown isotopes is presented for the first time: ^{72}Rb with 14 observed events and ^{77}Zr with one observed event. From the nonobservation of the less proton-rich nucleus ^{73}Rb, we derive an upper limit for the ground-state half-life of 81xa0ns, consistent with the previous upper limit of 30xa0ns. For ^{72}Rb, we have measured a half-life of 103(22)xa0ns. This observation of a relatively long-lived odd-odd nucleus, ^{72}Rb, with a less exotic odd-even neighbor, ^{73}Rb, being unbound shows the diffuseness of the proton drip line and the possibility of sandbanks to exist beyond it. The ^{72}Rb half-life is consistent with a 5^{+}→5/2^{-} proton decay with an energy of 800-900xa0keV, in agreement with the atomic mass evaluation proton-separation energy as well as results from the finite-range droplet model and shell model calculations using the GXPF1A interaction. However, we cannot explicitly exclude the possibility of a proton transition between 9^{+}(^{72}Rb)→9/2^{+}(^{71}Kr) isomeric states with a broken mirror symmetry. These results imply that ^{72}Kr is a strong waiting point in x-ray burst rp-process scenarios.