Engineering topics
Isobe, T.
Publications and source records attributed to Isobe, T..
Observation of new neutron-rich Mn, Fe, Co, Ni, and Cu isotopes in the vicinity of Ni 78
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Pion production in rare-isotope collisions
Pion energy spectra are presented for central collisions of neutron-rich 132 Sn + 124 Sn and neutron-deficient 108 Sn + 112 Sn systems using simulations with the Boltzmann-Uehling-Uhlenbeck transport model. These calculations, which incorporate isospin-dependent mean-field potentials for relevant baryons and mesons, display a sensitivity to the pion spectra that could allow significant constraints on the density dependence of the symmetry energy and its mean-field potential at suprasaturation densities. As a result, the predicted sensitivity increases with the isospin asymmetry of the total system and decreases with incident energy.
The role of core excitations in the structure and decay of the 16+ spin-gap isomer in 96Cd
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KATANA – A charge-sensitive triggering system for the SπRIT experiment
KATANA - the Krakow Array for Triggering with Amplitude discrimiNAtion - has been built and used as a trigger and veto detector for the SπRIT TPC at RIKEN. Its construction allows operating in magnetic field and providing fast response for ionizing particles, giving an approximate forward multiplicity and charge information. Depending on this information, trigger and veto signals are generated. The article presents performance of the detector and details of its construction. A simple phenomenological parametrization of the number of emitted scintillation photons in plastic scintillator is proposed. The effect of the light output deterioration in the plastic scintillator due to the in-beam irradiation is discussed.
94 {beta}-Decay Half-Lives of Neutron-Rich 55Cs to 67Ho: Experimental Feedback and Evaluation of the r-Process Rare-Earth Peak Formation
The β-decay half-lives of 94 neutron-rich nuclei 144$-$151 Cs, 146$-$154 Ba, 148$-$156 La, 150$-$158 Ce, 153$-$160 Pr, 156$-$162 Nd, 159$-$163 Pm, 160$-$166 Sm, 161$-$168 Eu, 165$-$170 Gd, 166$-$172 Tb, 169$-$173 Dy, 172$-$175 Ho, and two isomeric states 174m Er, 172m Dy were measured at the Radioactive Isotope Beam Factory, providing a new experimental basis to test theoretical models. Strikingly large drops of β-decay half-lives are observed at neutron-number N = 97 for 58 Ce, 59 Pr, 60 Nd, and 62 Sm, and N = 105 for 63 Eu, 64 Gd, 65 Tb, and 66 Dy. Lastly, features in the data mirror the interplay between pairing effects and microscopic structure. r-process network calculations performed for a range of mass models and astrophysical conditions show that the 57 half-lives measured for the first time play an important role in shaping the abundance pattern of rare-earth elements in the solar system
A gating grid driver for time projection chambers
A simple but novel driver system has been developed to operate the wire gating grid of a Time Projection Chamber (TPC). This system connects the wires of the gating grid to its driver via low impedance transmission lines. When the gating grid is open, all wires have the same voltage allowing drift electrons, produced by the ionization of the detector gas molecules, to pass through to the anode wires. When the grid is closed, the wires have alternating higher and lower voltages causing the drift electrons to terminate at the more positive wires. Rapid opening of the gating grid with low pickup noise is achieved by quickly shorting the positive and negative wires to attain the average bias potential with N-type and P-type MOSFET switches. The circuit analysis and simulation software SPICE shows that the driver restores the gating grid voltage to 90% of the opening voltage in less than 0.20 µs, for small values of the termination resistors. When tested in the experimental environment of a time projection chamber larger termination resistors were chosen so that the driver opens the gating grid in 0.35 µs. In each case, opening time is basically characterized by the RC constant given by the resistance of the switches and terminating resistors and the capacitance of the gating grid and its transmission line. By adding a second pair of N-type and P-type MOSFET switches, the gating grid is closed by restoring 99% of the original charges to the wires within 3 µs.
Isomer spectroscopy of neutron-rich $^{165,167}$Tb
We present information on the excited states in the prolate-deformed, neutron-rich nuclei 165,167 Tb 100,102 . The nuclei of interest were synthesised following in-flight fission of a 345 MeV per nucleon 238 U primary beam on a 2 mm 9 Be target at the Radioactive Ion-Beam Factory (RIBF), RIKEN, Japan. The exotic nuclei were separated and identified event-by-event using the BigRIPS separator, with discrete energy gamma-ray decays from isomeric states with half-lives in the μs regime measured using the EURICA gamma-ray spectrometer. Metastable-state decays are identified in 165 Tb and 167 Tb and interpreted as arising from hindered E1 decay from the 72 – [523] single quasi-proton Nilsson configuration to rotational states built on the 32 – [411] single quasi-proton ground state. Lastly, these data correspond to the first spectroscopic information in the heaviest, odd-A terbium isotopes reported to date and provide information on proton Nilsson configurations which reside close to the Fermi surface as the 170 Dy doubly-midshell nucleus is approached.
K-mixing in the doubly mid-shell nuclide 170Dy and the role of vibrational degeneracy
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Proton-hole and core-excited states in the semi-magic nucleus 131In82
The decay of the N = 83 nucleus Cd-131 has been studied at the RIBF facility at the RIKEN Nishina Center. The main purpose of the study was to identify the position of the and proton-hole states and the energies of core-excited configurations in the semi-magic nucleus In-131. From the radiation emitted following the decay, a level scheme of In-131 was established and the feeding to each excited state determined. Similarities between the single-particle transitions observed in the decays of the N = 83 isotones In-132 and Cd-131 are discussed. Finally the excitation energies of several core-excited configurations in In-131 are compared to QRPA and shell-model calculations.
Long-lived K isomer and enhanced γ vibration in the neutron-rich nucleus 172 Dy: Collectivity beyond double midshell
The level structure of 172Dy has been investigated for the first time by means of decay spectroscopy following in-flight fission of a 238U beam. A long-lived isomeric state with T1/2 = 0.71(5) s and Kπ = 8- has been identified at 1278 keV, which decays to the ground-state and γ -vibrational bands through hindered electromagnetic transitions, as well as to the daughter nucleus 172Ho via allowed β decays. The robust nature of the Kπ = 8- isomer and the ground-state rotational band reveals an axially-symmetric structure for this nucleus. Meanwhile, the γ -vibrational levels have been identified at unusually low excitation energy compared to the neighboring well-deformed nuclei, indicating the significance of the microscopic effect on the non-axial collectivity in this doubly mid-shell region. The underlying mechanism of enhanced γ vibration is discussed in comparison with the deformed Quasiparticle Random-Phase Approximation based on a Skyrme energy-density functional.
β decay of semi-magic Cd 130 : Revision and extension of the level scheme of In 130
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Status and results from the decay spectroscopy project EURICA (Euroball-RIKEN cluster array)
β- and isomer-decay spectroscopy are sensitive probes of nuclear structure, and are often the only techniques capable of providing data for exotic nuclei that are produced with very low rates. Decay properties of exotic nuclei are also essential to model astrophysical events responsible for the evolution of the universe such as the rp- and r-processes. The EURICA project (EUROBALL RIKEN Cluster Array) has been launched in 2012 with the goal of performing spectroscopy of very exotic nuclei. Since 2012, five experimental campaigns have been successfully completed using fragmentation of {sup 124}Xe beam and in-flight-fission of {sup 238}U beam. In these proceedings we will introduce the experimental setup and highlight some key recent results around {sup 78}Ni, {sup 132}Sn, and {sup 110}Zn published during 2014 and 2015.
Two-hole structure outside Ni 78 : Existence of a μ s isomer of Co 76 and β decay into Ni 76
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Extension of the N = 40 Island of Inversion towards N = 50 : Spectroscopy of Cr 66 , Fe 70 , 72
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Lifetime measurements of the first 2 + states in 104,106Zr: Evolution of ground-state deformations
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Heavy rotation – evolution of quadrupole collectivity centred at the neutron-rich doubly mid-shell nucleus {sup 170}Dy
In this contribution the low-excitation structural properties of the doubly mid-shell nucleus {sup 170}Dy are discussed, with a special empasis on the evolution of the ground state rotational band within the dysprosium isotopic chain. Recent results from an experiment with the EURICA setup at RIKEN are shown in the context of previous measurements at the PRISMA+CLARA as well as the PRISMA+AGATA setups at Laboratori Nazionali di Legnaro. A brief outlook on future planned measurements is also given.