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International audience; The β decay of Te90142 to I89142 was investigated for the first time. The parent nucleus was produced by the in-flight fission of a U238 beam with an energy of 345 MeV per nucleon, impinging on a Be9 target at the Radioactive Isotope Beam Factory of RIKEN. Excited states in I142 were established by β-delayed γ-ray spectroscopy. The observed (1+) states in I142 could be interpreted to be predominantly the ν0h9/2⊗π0h11/2 configuration formed by a Gamow-Teller transition between a neutron in the 0h9/2 orbital and a proton in the 0h11/2 orbital. Additional features of the (1+) states are discussed by comparing with neighboring heavier isotones, such as Cs144 and La146. In the context of deformed shell-model calculations, the (11+) state is closely related to the ν[5,3,2]3/2⊗π[5,5,0]1/2 configuration, which may be related to the weak Gamow-Teller transition strength.

International audience; The β-decay scheme of Te138 and the level structure of I138 is reported for the first time. The experiment was performed at the Radioactive Isotope Beam Factory of RIKEN, as one of the EUROBALL-RIKEN Cluster Array campaigns. Secondary radioactive ions, including Te138 and Sb138, were produced by the in-flight fission of a U238 beam with the energy of 345 MeV per nucleon. From the β decay of Te138, the level scheme of I138 was supplemented with new spin and parity assignments, such as the low-lying negative-parity states and a positive-parity 1+ state. This 1+ state can be interpreted as being associated with the π0h11/2⊗ν0h9/2 partner orbital configuration populated by the Gamow-Teller transition between a neutron in the 0h9/2 orbital and a proton in the 0h11/2 orbital. Details of the structure of I138 are discussed in terms of the proton-neutron interactions and Gamow-Teller transition strength within the theoretical context of shell-model calculations.

The neutron-rich dysprosium isotopes ¹⁶⁸Dy₁₀₂ and ¹⁶⁹Dy₁₀₃ have been investigated using the EURICA γ-ray spectrometer, following production via in-flight fission of a high-intensity uranium beam in conjunction with isotope separation through the BigRIPS separator at RIBF in RIKEN Nishina Center. For ¹⁶⁸Dy, a previously unreported isomer with a half-life of 0.57(7) μs has been identified at an excitation energy of 1378 keV, and its presence affirmed independently using γ-γ-γ coincidence data taken with Gammasphere via two-proton transfer from an enriched ¹⁷⁰Er target performed at Argonne National Laboratory. This isomer is assigned Jπ = Kπ = (4⁻) based on the measured transition strengths, decay patterns, and the energy systematics for two-quasiparticle states in N = 102 isotones. The underlying mechanism of two-quasiparticle excitations in the doubly midshell region is discussed in comparison with the deformed QRPA and multi-quasiparticle calculations. In ¹⁶⁹Dy, the B(E2) value for the transition de-exciting the previously unreported Kπ = (1/2⁻) isomeric state at 166 keV to the Kπ = (5/2⁻) ground state is approximately two orders of magnitude larger than the E2 strength for the corresponding isomeric-decay transition in the N = 103 isotone ¹⁷³Yb, suggesting the presence of a significant γ-vibrational admixture with a dominant neutron one-quasiparticle component in the isomeric state.

Excited states have been studied in \iso{159}{Sm}, \iso{161}{Sm}, \iso{162}{Sm} (Z~=~62), \iso{163}{Eu} (Z~=~63), and \iso{164}{Gd} (Z~=~64), populated by isomeric decay following 238U projectile fission at RIBF, RIKEN. The isomer half-lives range from 50 ns to 2.6 \mus. In comparison with other published data, revised interpretations are proposed for \iso{159}{Sm} and \iso{163}{Eu}. The first data for excited states in \iso{161}{Sm} are presented, where a 2.6 \mus isomer is assigned a three-quasiparticle, K^\pi = 17/2^- structure. The interpretation is supported by multi-quasiparticle Nilsson-BCS calculations, including the blocking of pairing correlations. A consistent set of reduced E1 hindrance factors is obtained. Limited evidence is also reported for isomeric decay in 163Sm, 164Eu and 165Eu.

The -decay half-lives of 94 neutron-rich nuclei 144−151Cs, 146−154Ba, 148−156La, 150−158Ce, 153−160Pr, 156−162Nd, 159−163Pm, 160−166Sm, 161−168Eu, 165−170Gd, 166−172Tb, 169−173Dy, 172−175Ho and two isomeric states 174mEr, 172mDy were measured at Radioactive Isotope Beam Factory (RIBF), providing a new experimental basis to test theoretical models. Striking, large drops of -decay half-lives are observed at neutron-number N = 97 for 58Ce, 59Pr, 60Nd, 62Sm, and N = 105 for 63Eu, 64Gd, 65Tb, 66Dy. 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.

International audience; The β-decay half-lives of 94 neutron-rich nuclei 144−151Cs, 146−154Ba, 148−156La, 150−158Ce, 153−160Pr, 156−162Nd, 159−163Pm, 160−166Sm, 161−168Eu, 165−170Gd, 166−172Tb, 169−173Dy, 172−175Ho, and two isomeric states 174mEr, 172mDy 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 58Ce, 59Pr, 60Nd, and 62Sm, and N=105 for 63Eu, 64Gd, 65Tb, and 66Dy. 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.

KOBRA (KOrea Broad acceptance Recoil spectrometer and Apparatus) facility being designed at Rare Isotope Science Project in Korea will be utilized to produce rare isotope beams by employing multi-nucleon transfer reactions at about 20 MeV/nucleon for studies of nuclear structure. KOBRA will also provide high suppression of beam induced background for direct measurements of radiative-capture cross sections in the astrophysical energy range. The present design status of the KOBRA facility is reported along with a brief introduction to the facility. We have studied the feasibility of production of 44Ti based on the present design of KOBRA as an example, and calculated the intensity of 44Ti secondary beam, to be about 105 particles per second, for 1 pnA 46Ti primary beam with a carbon target for a beam energy of 25 MeV/nucleon. A Monte Carlo simulation with a ray-tracing code has been performed to show that recoil products 66Se are well separated from a 65As beam by KOBRA for the 65As(p,γ)66Se reaction at a beam energy of 1 MeV/nucleon. © 2015 Elsevier B.V. All rights reserved.

International audience; In this article we report on the first spectroscopic information on 14051Sb89 and the observation of an isomer in this nucleus with T1/2=41(8) μs. It is located in close proximity to 140Sn for N=90, where the νf7/2 orbit is completely filled. The possible origin of the isomeric state is a πg17/2×νf−17/2 coupling configuration, resulting in a (6−) or (7−) spin-parity. This is likely caused by an inversion of the πg7/2 and πd5/2 orbitals at N=89. The existence of such an isomer far from stability is discussed extensively in the context of shell-model calculations and compared to results from mean-field calculations performed using a deformed Woods-Saxon potential. Both approaches suggest the observation of a single-particle excitation mode at an extreme neutron number.

We study for the first time the internal structure of 140Te through the beta-delayed gamma-ray spectroscopy of 140Sb. The very neutron-rich 140Sb, Z = 51 and N = 89, ions were produced by the in-flight fission of 238U beam on a 9Be target at 345 MeV per nucleon at the Radioactive Ion Beam Factory, RIKEN. The half-life and spin-parity of 140Sb are reported as 124(30) ms and (4-), respectively. In addition to the excited states of 140Te produced by the beta-decay branch, the beta-delayed one-neutron and two-neutron emission branches were also established. By identifying the first 2+ and 4+ excited states of 140Te, we found that Te isotopes persist their vibrator character with E(4+)/E(2+) = 2. We discuss the distinctive features manifest in this region, such as valence neutron symmetry and asymmetry, revealed in pairs of isotopes with the same neutron holes and particles with respect to N = 82., 9 pages, 6 figures, EURICA campaign

A new isomer with a half-life of 23.0(8) ms has been identified at 2406 keV in (126)Pd and is proposed to have a spin and parity of 10(+) with a maximally aligned configuration comprising two neutron holes in the 1h(11/2) orbit. In addition to an internal-decay branch through a hindered electric octupole transition, β decay from the long-lived isomer was observed to populate excited states at high spins in (126)Ag. The smaller energy difference between the 10(+) and 7(-) isomers in (126)Pd than in the heavier N=80 isotones can be interpreted as being ascribed to the monopole shift of the 1h(11/2) neutron orbit. The effects of the monopole interaction on the evolution of single-neutron energies below (132)Sn are discussed in terms of the central and tensor forces. ispartof: Physical Review Letters vol:113 issue:4 ispartof: location:United States status: published

High-spin states populated in the decay of microsecond isomers in the transitional nuclei Sb121 and Sb123 have been investigated in detail in several experiments using γ-ray and electron spectroscopy. The nuclei were formed using multinucleon transfer and fusion-fission reactions with Xe136 beams and also using the Sn120(Li7,α2n)Sb121 and Sn122(Li7,α2n)Sb123 incomplete-fusion reactions. Isomeric half-lives ranging from several nanoseconds to a few hundred microseconds were determined by means of conventional decay curve analyses, whereas very short-lived isomers (T1/2~1 ns) were identified using the generalized centroid-shift method. A number of new transitions were observed, including a branch through spherical states from the 19/2+ member of the 9/2+ deformed band in Sb121, in competition with the main decay path through the rotational band. This is attributed to mixing between the 19/2+ band member and a 19/2+ spherical state. Both levels are predicted to coincide approximately in energy in Sb121. The fact that a 25/2+ isomer occurs for A=121 and the lighter isotopes, while a 23/2+ isomer is observed for A=123-131 is explained through a multistate mixing calculation, taking into account the gradual shift of the 2d5/2 and 1g7/2 proton orbitals and the change in proton-neutron effective interactions from an attractive particle-particle type in the lower part of the shell to a repulsive particle-hole type with increasing the neutron number toward the N=82 shell closure. The observed enhancement of the B(E2;19/2-→15/2-) values in Sb121 and Sb123 over the B(E2;7-→5-) values in the corresponding Sn cores is discussed in terms of configuration mixing between spherical and deformed states.