Anisotropy in the arrival directions of cosmic rays with energies above 10 17 eV is studied using data from the Akeno 20 km 2 array and the Akeno Giant Air Shower Array (AGASA), using a total of about 114,000 showers observed over 11 years. In the first harmonic analysis, we have found strong anisotropy of ∼ 4% around 10 18 eV, corresponding to a chance probability of ∼ 0.2% after taking the number of independent trials into account. With two dimensional analysis in right ascension and declination, this anisotropy is interpreted as an excess of showers near the directions of the Galactic Center and the Cygnus region.

Using data from more than ten-years of observations with the Akeno Giant Air Shower Array (AGASA), we published a result that the energy spectrum of ultra-high energy cosmic rays extends beyond the cutoff energy predicted by Greisen, and Zatsepin and Kuzmin. In this paper, we reevaluate the energy determination method used for AGASA events with respect to the lateral distribution of shower particles, their attenuation with zenith angle, shower front structure, delayed particles observed far from the core and other factors. The currently assigned energies of AGASA events have an accuracy of $\pm$25% in event-reconstruction resolution and $\pm$18% in systematic errors around 10$^{20}$eV. This systematic uncertainty is independent of primary energy above 10$^{19}$eV. Based on the energy spectrum from 10$^{14.5}$eV to a few times 10$^{20}$eV determined at Akeno, there are surely events above 10$^{20}$eV and the energy spectrum extends up to a few times 10$^{20}$eV without a GZK-cutoff.Comment: accepted to Astroparticle Physics, 29pages, 17+1 figures, elsart.cls The AGASA exposure is 5.1x10^16 m2 sr s until July 200

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.

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 new technique to measure (p,n) charge-exchange reactions in inverse kinematics at intermediate energies on unstable isotopes was successfully developed and used to study the (56)Ni(p,n) reaction at 110 MeV/u. Gamow-Teller transition strengths from (56)Ni leading to (56)Cu were obtained and compared with shell-model predictions in the pf shell using the KB3G and GXPF1A interactions. The calculations with the GXPF1A interaction reproduce the experimental strength distribution much better than the calculations that employed the KB3G interaction, indicating deficiencies in the spin-orbit and proton-neutron residual potentials for the latter. The results are important for improving the description of electron-capture rates on nuclei in the iron region, which are important for modeling the late evolution of core-collapse and thermonuclear supernovae.