T. Ishii

Indications of neutrino oscillation in a 250 km long-baseline experiment.

The K2K experiment observes indications of neutrino oscillation: a reduction of nu(mu) flux together with a distortion of the energy spectrum. Fifty-six beam neutrino events are observed in Super-Kamiokande (SK), 250 km from the neutrino production point, with an expectation of 80.1(+6.2)(-5.4). Twenty-nine one ring mu-like events are used to reconstruct the neutrino energy spectrum, which is better matched to the expected spectrum with neutrino oscillation than without. The probability that the observed flux at SK is explained by statistical fluctuation without neutrino oscillation is less than 1%.

Search for Proton Decay via

We have searched for proton decay via p→νK+ using Super-Kamiokande data from April 1996 to February 2013, 260 kiloton•year exposure in total. No evidence for this proton decay mode is found. A lower limit of the proton lifetime is set to τ/B(p→νK+)>5.9×1033 years at 90% confidence level.

p \rightarrow \nu K^{+}

Abstract A new instrument, isomer-scope, has been constructed to observe the ns-μs isomers produced by deep inelastic collisions. It consists of a Si detector, a γ-absorber and Ge detectors. The Si detector provides the energy and timing signals of projectile-like fragments(PLF) for the coincidence measurement and also stores the isomers of PLF for the Ge detectors. The γ-absorber shields the Ge detectors from the strong γ-radiation generated in the target. Thus, the isomer-scope greatly intensifies the γ-rays from the isomers of PLF in the PLF-γ(-γ) coincidences. In the reaction 635 MeV 76 Ge + 198 Pt , a new isomer of 69 Cu was found to be excited at 2741 keV. It decayed with T 1 2 = 0.36(3) μ s via transition cascade 190-680-1871 and via cascade 73-486-471-1711. The cascade 486-471-1711 was fed in part from another state; either the 486 keV γ-ray or a side-feeding γ-ray unobserved was an isomeric transition of T 1 2 = 25(5) ns .

using 260 kiloton

Abstract An independently phased heavy ion linac composed of 46 superconducting quarter wave resonators has been built as a booster for the tandem accelerator at Japan Atomic Energy Research Institute, Tokai. Several kinds of heavy ions from Si to Au have been accelerated. The performances of the resonators and the cryogenic system, the method of setting resonator phases and the results of the beam acceleration tests are described.

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High-spin states of148Tb were studied by inbeam γ-ray spectroscopic techniques using141Pr(13C,6n)148Tb and27Al(130Te,9n)148Tb reactions. The level scheme of148Tb was established up to the excitation energy of 11.8MeV. The excitation energy of the high-spin isomer reported previously was revised to be 8.620MeV. The excited states below the isomer could be understood as resulted from the weak couplings of πh11/2 and νf7/2 to those of147Gd and147Tb, respectively.

year data of Super-Kamiokande

The present method of analyzing the decay curves is a direct extension of the method of linearizing an exponential decay using a semilog plot. On semilog graph paper experimental points of a decay curve can be approximated using a smooth curve having a slowly varying slope with recoil distance. In addition, the lifetime of an excited state can be expressed as the product of two factors: the reciprocal of the slope of a semilog graph and a correction factor for feeding time. These factors can be evaluated from two semilog graphs for the successive transitions, feeding and de-exciting a given excited state. This factorization simplifies the analysis of the decay curves and brings the method a considerable tolerance as regards their experimental errors. The present method has been applied to the decay curves measured in 124,126Ce and 132,134Nd.

Isomer-scope: A new instrument for in-beam γ-ray spectroscopy through deep inelastic collisions

The K2K long-baseline neutrino oscillation experiment uses a Scintillating Fiber Detector (SciFi) to reconstruct charged particles produced in neutrino interactions in the near detector. We describe the track reconstruction algorithm and the performance of the SciFi after 3 years of operation.

Acceleration of heavy ions by the JAERI tandem superconducting booster

Data on B(E2), B(M1) and B(E1) were obtained from lifetime measurements in 103, 105, 107In, 105-108Sn and 109Sb. These data helped us to assign the nuclear configurations to the involved states. The experimental B(E2) and B(M1) values in the Sn isotopes worked as litmus paper to test the wave functions calculated on the basis of the shell model. The present calculation gave a qualitative description of M1 transitions in the Sn isotopes but has not yet succeeded in quantitative estimation of B(M1). Calculated B(E2) values were far from the reality since 100Sn was assumed there to be inert against excitation.

High-spin states in148Tb

High-spin states in107Sn were studied using the reaction54Fe(56Fe, 2pn)107Sn. An odd-parity band was identified as based on thevh11/2 orbit by measuring theγ-ray linear polarization. Also were confirmed the excited states based on thevd5/2 andvg7/2 orbits. The halflives of the 17/2+ and 11/2− states were measured to be 0.25(4) ns and 28(11) ps, respectively. The experimental level structure and its interpretation were in good agreement with a shell model calculation.

A graphical analysis of decay curves measured by the Doppler-shift recoil distance method

High spin states in the isotopes105,103In have been studied by in-beamγ-ray techniques. The reaction51V(58Ni, 2p 2n) populated those states in105In. A measurement of the linear polarizations ofγ-rays has revealed a negative-parity band in105In. The reaction48Ti(58Ni,p 2n) produced the isotope103In, which has showed an yrast spectrum similar to that observed in105In. The lifetimes of the 19/2+ and 17/2+ states in107,105In have been measured by the recoil distance method;T1/2(19/2+)=27±4 ps andT1/2(17/2+)=1.1−0.3+0.6 ns for107In,T1/2(19/2+)=4±2 ps andT1/2(17/2+)=0.33±0.10 ns for105In.