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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.

Structure of the neutron-rich N=86 isotope 140Xe, located northeast of a doubly-magic nucleus 132Sn, is investigated by β−γ spectroscopy. Two β-decay isomers in 140I are newly found in the study of two different β decays of 140I which were produced by two reactions (i) direct in-flight fission at a primary target and (ii) β decay of 140Te at an active stopper. Half-lives of the β decays of the ground state, the low-spin isomer, and the high-spin isomer are determined to be 0.38(2), 0.91(5), and 0.47(4) s, respectively. Decay schemes of the β decay of the high-spin isomer and of the mixed β decays of the ground state and the low-spin isomer in 140I to 140Xe are constructed using the information on γ-ray coincidence relation and γ-ray intensity. Nuclear structures of the low-lying states in 140Xe and 140I are discussed by comparing the experimental results to two theoretical calculations based on a large-scale shell model and the deformed Skyrme Hartree-Fock-Bogoliubov plus deformed quasiparticle-random-phase approximation. Possible candidates for (quasi-)γ-band members of 2+ and 4+ states and the octupole collective 1− state are proposed in 140Xe. Increase of quadrupole, triaxial, and octupole collectivities is discussed with the increase of neutron and proton numbers.

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 β-decay scheme of 138Te and the level structure of 138I 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 138Te and 138Sb, were produced by the in-flight fission of a 238U beam with the energy of 345 MeV per nucleon. From the β decay of 138Te, the level scheme of 138I 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 138I are discussed in terms of the proton-neutron interactions and Gamow-Teller transition strength within the theoretical context of shell-model calculations.

The β-decay half-lives of 55 neutron-rich nuclei 134−139Sn, 134−142Sb, 137−144Te, 140−146I, 142−148Xe, 145−151Cs, 148−153Ba, and 151−155La were measured at the Radioactive Isotope Beam Factory employing the projectile fission fragments of 238U. The nuclear level structure, which relates to deformation, has a large effect on the half-lives. The impact of newly measured half-lives on modeling the astrophysical origin of the heavy elements is studied in the context of r process nucleosynthesis. For a wide variety of astrophysical conditions, including those in which fission recycling occurs, the half-lives have an important local impact on the second (A ≈ 130) peak.

We studied the production of neutron-rich nuclides in multinucleon transfer collisions of stable and radioactive beams (RIB) in the mass range A ∼ 40-60. We first presented our experimental cross section data of projectile fragments from the reaction of 40Ar(15 MeV/nucleon) with 64Ni, 58Ni and 27Al. We then compared them with calculations based on either the deep-inelastic transfer model or the constrained molecular dynamics model, followed by the statistical multifragmentation model. An overall good agreement of the calculations with the experimental data is obtained. We continued with calculations of the reaction of 40Ar (15 MeV/nucleon) with 238U target and then with reactions of 48Ca (15 MeV/nucleon) with 64Ni and 238U targets. In these reactions, very neutron-rich rare isotopes are produced with large cross sections. These nuclides, in turn, can be assumed to form RIB and interact with a subsequent target (preferably 238U), leading to the production of extremely neutron-rich and even new isotopes (e.g. 60Ca) in this mass range. We conclude that multinucleon transfer reactions with stable or RIB at energy around 15 MeV/nucleon offer an effective route to access extremely neutron-rich rare isotopes for nuclear structure or reaction studies. © 2018 IOP Publishing Ltd.

International audience; We study for the first time the internal structure of Te140 through the β-delayed γ-ray spectroscopy of Sb140. The very neutron-rich Sb140 nuclei with Z=51 and N=89 were produced by the in-flight fission of U238 beams at the Radioactive Isotope Beam Factory, RIKEN. The half-life and spin-parity of Sb140 are reported as 173±12 ms and 3−, respectively. In addition to the excited states of Te140 produced by the β-decay branch, the β-delayed one-neutron and two-neutron emission branches were also established. By identifying the first 2+ and 4+ excited states of Te140, we found that Te isotopes persist in their vibrator character with E(4+)/E(2+)=2. We discuss the distinctive features manifest in this region revealed in pairs of isotopes with the same neutron holes and particles with respect to N=82.

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.

We investigate the possibilities of producing neutron-rich nuclides in projectile fission of heavy beams in the energy range of 20 MeV/nucleon expected from low-energy facilities. We report our efforts to theoretically describe the reaction mechanism of projectile fission following a multinucleon transfer collision at this energy range. Our calculations are mainly based on a two-step approach: The dynamical stage of the collision is described with either the phenomenological deep-inelastic transfer model (DIT) or with the microscopic constrained molecular dynamics model (CoMD). The de-excitation or fission of the hot heavy projectile fragments is performed with the statistical multifragmentation model (SMM). We compared our model calculations with our previous experimental projectile-fission data of U238 (20 MeV/nucleon) + Pb208 and Au197 (20 MeV/nucleon) + Au197 and found an overall reasonable agreement. Our study suggests that projectile fission following peripheral heavy-ion collisions at this energy range offers an effective route to access very neutron-rich rare isotopes toward and beyond the astrophysical r-process path. © 2016 American Physical Society.

One-neutron knockout from 24 O leading to the first excited state in 23 O has been measured for a proton target at a beam energy of 62 MeV/nucleon. The decay energy spectrum of the neutron unbound state of 23 O was reconstructed from the measured four momenta of the 22 O fragment and emitted neutron. A sharp peak was found at Edecay=50±3 keV , corresponding to an excited state in 23 O at 2.78±0.11 MeV , as observed in previous measurements. The longitudinal momentum distribution for this state was consistent with d -wave neutron knockout, providing support for a Jπ assignment of 5/2+ . The associated spectroscopic factor was deduced to be C2S(0d5/2)=4.1±0.4 by comparing the measured cross section ( σ−1nexp=61±6 mb ) with a distorted wave impulse approximation calculation. Such a large occupancy for the neutron 0d5/2 orbital is in line with the N=16 shell closure in 24 O.