Beam and SKS spectrometers at the K1.8 beam line

High-resolution spectrometers for both incident beams and scattered particles have been constructed at the K1.8 beam line of the Hadron Experimental Facility at J-PARC. A point-to-point optics is realized between the entrance and exit of QQDQQ magnets for the beam spectrometer. Fine-pitch wire chamber trackers and hodoscope counters are installed in the beam spectrometer to accept a high rate beam up to 107 Hz. The superconducting kaon spectrometer for scattered particles was transferred from KEK with modifications to the cryogenic system and detectors. A missing-mass resolution of 1.9 ± 0.1 MeV/c2 (FWHM) was achieved for the ∑ peaks of (π±, K+) reactions on a proton target in the first physics run of E19 in 2010

Seepage induced displacements of suction caissons: FE analysis

Finite element analyses of suction caissons are performed under seepage flow in elastic soil. Poroelastic water elements are used underneath the caisson lid allowing for modelling of suction and inducing seepage flow into the caisson compartment. A detailed parametric study is undertaken exploring the effects of caisson aspect ratio, soil-caisson interface roughness, caisson inner ring stiffeners, and potential gap formation between caisson outer wall and soil, and soil permeability on caisson upward displacement. The results indicate that caisson roughness and stiffeners affect caisson displacement behaviour. A rough caisson causes earlier dissipation of suction hence caisson upward displacements are minimal for a rough caisson compared to a smooth caisson. A steady state seepage condition is only achieved for a smooth caisson with no stiffeners. Presence of stiffeners and surface roughness leads to a halt in caisson upward displacement. Any potential gap along the outer skirt interface enhances the upward displacement for a smooth non-stiffened caisson, but not for a caisson with stiffeners or a rough caisson. For the smooth non-stiffened caissons, unified equations are proposed to estimate seepage length and caisson displacement for soils with different permeabilities

Study of ¹⁹C by One-Neutron Knockout

21st International Conference on Few-Body Problems in Physics, Chicago, IL, USA, May 18-22, 2015.The spectroscopic structure of ¹⁹C, a prominent one-neutron halo nucleus, has been studied with a ²⁰C secondary beam at 290 MeV/nucleon and a carbon target. Neutron-unbound states populated by the one-neutron knockout reaction were investigated by means of the invariant mass method. The preliminary relative energy spectrum and parallel momentum distribution of the knockout residue, ¹⁹C∗, were reconstructed from the measured four momenta of the¹⁸C fragment, neutron, and beam. Three resonances were observed in the spectrum, which correspond to the states at Ex = 0.62(9), 1.42(10), and 2.89(10) MeV. The parallel momentum distributions for the 0.62-MeV and 2.89-MeV states suggest spin-parity assignments of 5/2⁺ and 1/2⁻, respectively. The 1.42-MeV state is in line with the reported 5/22⁺ state

Spectroscopy of ¹⁷C via one-neutron knockout reaction

21st International Conference on Few-Body Problems in Physics, Chicago, IL, USA, May 18-22, 2015.A spectroscopic study of ¹⁷C was performed via the one-neutron knockout reaction of ¹⁸C on a carbon target at RIKEN-RIBF. Three unbound states at excitation energies of 2.66(2), 3.16(5), and 3.97(3) MeV (preliminary) were observed. The energies are compared with shell-model calculations and existing measurements to deduce their spin-parities. From the comparison, the states at 2.66(2) and 3.97(3) MeV are suggested to be 1/2⁻ and 3/2⁻, respectively. From its decay property, the state at 3.16(5) MeV is indicated to be 9/2⁺

Identification of New Neutron-Rich Isotopes in the Rare-Earth Region Produced by 345 MeV/nucleon 238^{238}U

International audienceA search for new isotopes in the neutron-rich rare-earth region has been carried out using a 345 MeV=nucleon 238U beam at the RIKEN Nishina Center RI Beam Factory. Fragments produced were analyzed and identified using the BigRIPS in-flight separator. We observed a total of 29 new neutron-rich isotopes: 153Ba, 154,155,156La, 156,157,158Ce, 156,157,158,159,160,161Pr, 162,163Nd, 164,165Pm, 166,167Sm, 169Eu, 171Gd, 173,174Tb, 175,176Dy, 177,178Ho, and 179,180Er

Spectroscopy of C-17 Above the Neutron Separation Energy

Spectroscopy of an unbound nucleus C-17 was performed using the SAMURAI spectrometer at RIBF of RIKEN. Six resonances were observed for the C-16+n system with relative energies of 0.52, 0.77, 1.36, 1.91, 2.22 and 3.20 MeV. The excitation energies (E-x) of the observed resonances were deduced, by taking into account the states of the C-16 fragments identified by coincident gamma rays, as E-x =(3.02), 1.51, (3.86), 2.65, (4.72) and 3.94MeV. The orbital angular momenta of the two observed states in C-17 at E-x =2.65 and 3.94 MeV were determined as 1 by comparing parallel momentum distributions with theoretical predictions.11Nsciescopu

Study of 19^{19}C by One-Neutron Knockout from 20^{20}C

International audienceThe present work aims at exploring neutron-unbound states of 19C via the one-neutron knockout reaction. The invariant mass measurement in inverse kinematics was carried out with a carbon target and a 20C secondary beam at 290 MeV/nucleon. The preliminary relative energy spectrum and the parallel momentum distribution of the system of 18C + n were reconstructed from the measured momenta of the 18C fragment and decayed neutron. A new resonance was observed at Erel = 2.3 MeV, which corresponds to the unbound state of 19C at Ex = 2.9 MeV. The parallel momentum distribution for this resonance suggests a spin-parity assignment of 1/2−. Additionally, two known states were seen at Ex = 0.6 and 1.4 MeV, consistent with the 5/2+1 and 5/2+2 states, respectively

Spectroscopy of 17C via one-neutron knockout reaction

A spectroscopic study of 17C was performed via the one-neutron knockout reaction of 18C on a carbon target at RIKEN-RIBF. Three unbound states at excitation energies of 2.66(2), 3.16(5), and 3.97(3) MeV (preliminary) were observed. The energies are compared with shell-model calculations and existing measurements to deduce their spin-parities. From the comparison, the states at 2.66(2) and 3.97(3) MeV are suggested to be 1/2− and 3/2−, respectively. From its decay property, the state at 3.16(5) MeV is indicated to be 9/2+

Study of 19C by One-Neutron Knockout

The spectroscopic structure of 19C, a prominent one-neutron halo nucleus, has been studied with a 20C secondary beam at 290 MeV/nucleon and a carbon target. Neutron-unbound states populated by the one-neutron knockout reaction were investigated by means of the invariant mass method. The preliminary relative energy spectrum and parallel momentum distribution of the knockout residue, 19C*, were reconstructed from the measured four momenta of the 18C fragment, neutron, and beam. Three resonances were observed in the spectrum, which correspond to the states at Ex = 0.62(9), 1.42(10), and 2.89(10) MeV. The parallel momentum distributions for the 0.62-MeV and 2.89-MeV states suggest spin-parity assignments of 5/2+ and 1/2−, respectively. The 1.42-MeV state is in line with the reported 5/22+ state

Structure beyond the dripline in the Boron isotopes: 16;18;20;21^{16;18;20;21}B

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