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Vector analyzing power for the proton-6 He elastic scattering at 71 MeV/nucleon has been measured for the first time, with a newly developed polarized proton solid target working at 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 α-core distribution in 6 He is suggested to be a possible key to understand the nuclear structure sensitivity. PACS numbers: 24.70.+s, 29.25.Pj Spin observables in scattering experiments have been rich sources of our understanding of nuclear structure, reaction, and interactions. One of the good examples is spin asymmetry in proton-proton and proton-nucleus (p-A) scatterings which is a direct manifestation of spinorbit coupling in the system. The first spin asymmetry measurements carried out by use of a double scattering method [1,2] clearly demonstrated that the spin-orbit coupling in nuclei is an order of magnitude stronger than that due to the relativistic effect [3]. At present the spin-orbit coupling in p-A scattering is quantitatively established through numerous experiments using polarized proton beams for stable targets.It is interesting to use spin asymmetry measurements to study unstable nuclei. Nuclei locating near the neutron drip line occasionally show distinctive structure such as halos or skins. The neutron rich 6 He nucleus is one of the typical nuclides with an extended neutron distribution. Since the extended neutron distribution is prominent at the nuclear surface and the spin-orbit coupling is, in nature, a surface phenomenon, it is stimulating to see how the extended neutron distributions affect the spin asymmetry, i.e., vector analyzing power in proton elastic scattering.In this Letter, we report new results of vector analyzing power for the p-6 He elastic scattering at 71 MeV/nucleon, measured with a newly developed polarized proton target. The results are compared with microscopic folding model calculations.Although cross sections in proton elastic scattering from 6 He have been extensively measured over a wide range of energies [4][5][6][7][8][9], until recently there had been no measurement of vector analyzing power. Since unstable nuclei are produced as secondary beams, we need a polarized proton target, practically in the solid state, for the spin-asymmetry studies. In addition, the solid polarized proton target should work under a low magnetic field of B ∼ 0.1 T for detection of recoiled protons with magnetic rigidity as low as 0.3 Tm. The traditional dynamical nuclear polarization technique [10], demanding a magnetic field higher than a few Tesla, can not be applied therefore. Although this difficulty might be overcome by applying a "spin frozen" operation, efforts to do so have not been successful so far. An alternative approach to overcome the problem is to develop a polarized target based on a new principle which...

A search for isomeric γ-decays among fission fragments from 345 MeV/nucleon 238 U has been performed at the RIKEN Nishina Center RI Beam Factory. Fission fragments were selected and identified using the superconducting in-flight separator BigRIPS and were implanted in an aluminum stopper. Delayed γ-rays were detected using three clover-type high-purity germanium detectors located at the focal plane within a time window of 20 μs following the implantation. We identified a total of 54 microsecond isomers with half-lives of ~ 0. on the obtained spectroscopic information and the systematics in neighboring nuclei. Nature of the nuclear isomerism is discussed in relation to evolution of nuclear structure.KEYWORDS: Nuclear reactions Be( 238 U, x) and Pb( 238 U, x) E = 345 MeV/nucleon, in-flight fission, fission fragments, in-flight RI beam separator, short-lived isomers, new isomers, half-life, γ-ray relative intensity, γγ coincidence, proposed level schemes DOI: PACS number(s): 23.35.+g, 23.20.Lv, 29.38.Db _____________________ *

A search for new isotopes using in-flight fission of a 345 MeV/nucleon 238 U beam has been carried out at the RI Beam Factory at the RIKEN Nishina Center. Fission fragments were analyzed and identified by using the superconducting in-flight separator BigRIPS. We observed 45 new neutron-rich isotopes: Since the pioneering production of radioactive isotope (RI) beams in the 1980s, 1) studies of exotic nuclei far from stability have been attracting much attention. Neutron-rich exotic nuclei are of particular interest, because new phenomena such as neutron halos, neutron skins, and modifications of shell structure have been discovered.2-5) Furthermore these neutron-rich nuclei are important in relation to astrophysical interests, 6) because many of them play a role in the astrophysical r-process. 7) To make further advances in nuclear science and nuclear astrophysics, it is essential to expand the region of accessible exotic nuclei towards the neutron dripline. In-flight fission of a uranium beam is known to be an excellent mechanism for this purpose, having large production cross sections for neutron-rich exotic nuclei. became operational, in which the superconducting in-flight separator BigRIPS 10,11) has been used for the production of RI beams. The BigRIPS separator is designed as a two-stage separator with large acceptance, so that excellent features of in-flight fission can be exploited. In May 2007, right after the commissioning of the BigRIPS separator, we performed an experiment to search for new isotopes using in-flight fission of a 345 MeV/nucleon 238 U beam, aiming to expand the LETTERS Ã

The electric quadrupole transition from the first 2 + state to the ground 0 + state in 18 C was studied through a lifetime measurement by an upgraded recoil shadow method applied to inelastically scattered radioactive 18 C nuclei. The measured mean lifetime is 18.9 ± 0.9(stat) ± 4.4(syst) ps, corresponding to a B(E2; 2 + 1 → 0 + g.s. ) value of 4.3 ± 0.2 ± 1.0 e 2 fm 4 , or about 1.5 Weisskopf units. The mean lifetime of the first 2 + state in 16 C was remeasured to be 18.3 ± 1.4 ± 4.8 ps, about four times shorter than the value reported previously. The discrepancy between the two results was explained by incorporating the γ -ray angular distribution measured in this work into the previous measurement. These transition strengths are hindered compared to the empirical transition strengths, indicating that the anomalous hindrance observed in 16 C persists in 18 C.