Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1103/PhysRevC.103.034327

Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1103/PhysRevC.103.034320

Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1103/PhysRevC.103.014614

Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1103/PhysRevC.102.034314

Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1103/PhysRevC.102.034324

Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1103/PhysRevC.101.044311

Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1103/PhysRevC.101.042801

Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1103/PhysRevLett.124.112501

Language：English   Publishing type：Research paper (scientific journal)  

The β-ray detected nuclear magnetic resonance (β-NMR) of a short lived-nucleus ¹⁷N (I = 1/2, T_1/2 = 4.173 s) in liquid H₂O and CH₃NO₂ has been performed. A π-pulse method was applied to obtain sharp NMR lines, from which the ratio of the Larmor frequencies of ¹⁷N in CH₃NO₂ and ¹H was determined to be ν[¹⁷N in CH₃NO₂]/ν[¹H₂O] = 0.1265751 ± 0.0000019. Two resonance lines were observed for ¹⁷N in H₂O with the relative frequency shifts of –(2.33 ± 0.37) × 10⁻⁴ and (2.91 ± 0.27) × 10⁻⁴ referenced to ¹⁷N in CH₃NO₂.

DOI： 10.1007/s10751-019-1650-3

Language：English   Publishing type：Research paper (scientific journal)  

A systematic study was performed of microsecond γ-decaying isomers around Sn100 produced in a fragmentation reaction of a Xe124 beam at 345 MeV/u at the Radioactive Ion Beam Factory of the RIKEN Nishina Center in Saitama, Japan. Half-lives of isomeric states in that region were remeasured allowing us to improve the currently available experimental information. Reduced transition probabilities were deduced and compared to shell-model calculations in various model spaces. The recently reported low-energy transitions in Rh92 and Ag96 were remeasured with improved precision. Additionally, experimental information on isomeric ratios, including five new ones, were extracted and compared to a previous experimental study and the sharp cutoff model of fragmentation reaction.

DOI： 10.1103/PhysRevC.100.024302

Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1103/PhysRevLett.122.212502

Language：English   Publishing type：Research paper (scientific journal)  

The neutron-rich isotopes of palladium have attracted considerable interest in terms of the evolution of the N=82 neutron shell closure and its influence on the r-process nucleosynthesis. In this Letter, we present the first spectroscopic information on the excited states in ¹²⁵ Pd ₇₉ and ¹²⁷ Pd ₈₁ studied using the EURICA γ-ray spectrometer, following production via in-flight fission of a high-intensity ²³⁸ U beam at the RIBF facility. New isomeric states with half-lives of 144(4) ns and 39(6) μs have been assigned spins and parities of (23/2 ⁺ ) and (19/2 ⁺ ) in ¹²⁵ Pd and ¹²⁷ Pd, respectively. The observed level properties are compared to a shell-model calculation, suggesting the competition between proton excitations and neutron excitations in the proton-hole and neutron-hole systems in the vicinity of the doubly magic nucleus ¹³² Sn.

DOI： 10.1016/j.physletb.2019.03.053

Language：English   Publishing type：Research paper (scientific journal)  

The β-delayed γ-ray spectroscopy of neutron-rich Ag123,125 isotopes is investigated at the Radioactive Isotope Beam Factory of RIKEN, and the long-predicted 1/2- β-emitting isomers in Ag123,125 are identified for the first time. With the new experimental results, the systematic trend of energy spacing between the lowest 9/2+ and 1/2- levels is extended in Ag isotopes up to N=78, providing a clear signal for the reduction of the Z=40 subshell gap in Ag towards N=82. Shell-model calculations with the state-of-the-art VMU plus M3Y spin-orbit interaction give a satisfactory description of the low-lying states in Ag123,125. The tensor force is found to play a crucial role in the evolution of the size of the Z=40 subshell gap. The observed inversion of the single-particle levels around Ag123 can be well interpreted in terms of the monopole shift of the π1g9/2 orbitals mainly caused by the increasing occupation of ν1h11/2 orbitals.

DOI： 10.1103/PhysRevLett.122.212502

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.5506/APhysPolB.50.431

Language：English   Publishing type：Research paper (scientific journal)  

A γ-decaying isomeric state (τ1/2=197-17+19 ns) has been identified in Cd96, which is one α particle away from the last known bound N=Z nucleus, Sn100. Comparison of the results with shell-model calculations has allowed a tentative experimental level scheme to be deduced and the isomer to be interpreted as a medium-spin negative-parity spin trap based on the coupling of isoscalar (T=0) and isovector (T=1) neutron-proton pairs. The data also suggest evidence for the population of a 9+ T=1 state, which is predicted by shell-model calculations to be yrast. Such a low-lying T=1 state, which is unknown in lighter mass even-even self-conjugate nuclei, can also be interpreted in terms of the coupling of T=0 and T=1 neutron-proton pairs.

DOI： 10.1103/PhysRevC.99.021302

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We report on a new in situ laser spectroscopy technique using superfluid helium and a highly energetic ion beam. In taking advantage of superfluid helium as a host matrix for laser spectroscopy, we were able to develop an extremely low background detection system. The first demonstration using ⁸⁵ Rb ³¹⁺ ion beam (66 MeV/nucleon) accelerated at the RIKEN accelerator facility shows improvement of detection limit by two orders of magnitude. A quantitative evaluation of Rb atoms in the observation region enables an analysis of their optical absorption cross-section in superfluid helium from the fluorescence intensity dependence on ion-beam intensity and applied laser power.

DOI： 10.7567/1882-0786/aaf0a9

Language：English   Publishing type：Research paper (scientific journal)  

The nuclear g factor and quadrupole moment (Q_s) have been measured for the low-lying isomeric 1⁺ state of ³⁴Al, using the β-detected nuclear magnetic resonance (β-NMR) and quadrupole resonance (β-NQR) methods. Spin-polarized ³⁴Al isotopes were produced in a one-neutron pickup reaction induced by a ³⁶S beam on a ⁹Be target at a kinetic energy of 77.5 MeV/nucleon, and were collected with the LISE fragment separator at GANIL. The measured g factor (|g| in a range of 1.757±0.014) and quadrupole moment (|Q_s|=38(5) mb) are in good agreement with shell-model calculations using effective interactions. The similarity between the g factor of ^34mAl and that of ³²Al confirms a dominant neutron 2p1h configuration π(d_5/2)⁻¹⊗ν(d_3/2)⁻¹(f_7/2)² of ^34mAl. In addition, the enhanced quadrupole moment of ^34mAl relative to that of ³²Al suggests that the neutron 1p1h excitation across the N=20 shell gap introduces extra nucleon–nucleon correlation and deformation.

DOI： 10.1016/j.physletb.2018.06.009

Language：English   Publishing type：Research paper (scientific journal)  

Excited states in the neutron-rich nucleus ¹⁵⁰Ba have been observed via β–γ spectroscopy at the Radioactive Isotope Beam Factory, RIKEN Nishina Center. The ¹⁵⁰Ba ions were produced by the in-flight fission of a ²³⁸U beam with an energy of 345 MeV/nucleon. The E(2⁺) energy of ¹⁵⁰Ba was identified at 100 keV, which is the lowest known in the neutron-rich Ba isotopes. A γ-ray peak was also observed at 597 keV. A mean-field calculation with a fully 3D real space was performed and a static octupole deformation was obtained for the Ba isotopes. K^π = 0− and 1− excited states with significant octupole collectivity were newly predicted at around or lower than 1 MeV on the ground state of ¹⁵⁰Ba by a random-phase approximation calculation. The 597 keV γ ray can be interpreted as a negative-parity state, showing that ¹⁵⁰Ba may possess octupole collectivity.

DOI： 10.1093/ptep/pty037

Language：English   Publishing type：Research paper (scientific journal)  

A 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, ^{156,157,158,159,160,161}Pr, ^162,163Nd, ^164,165Pm, ^166,167Sm, ¹⁶⁹Eu, ¹⁷¹Gd, ^173,174Tb, ^175,176Dy, ^177,178Ho, and ^179,180Er.

DOI： 10.7566/JPSJ.87.014202

Language：English   Publishing type：Research paper (scientific journal)  

The search for new isotopes using the in-flight fission of a ²³⁸U beam has been conducted concurrently with decay measurements, during the so-called EURICA campaigns, at the RIKEN Nishina Center RI Beam Factory. Fission fragments were analyzed and identified in flight using the BigRIPS separator. We have identified the following 36 new neutron-rich isotopes: ¹⁰⁴Rb, ¹¹³Zr, ¹¹⁶Nb, ^118,119Mo, ^121,122Tc, ¹²⁵Ru, ^127,128Rh, ^129,130,131Pd, ¹³²Ag, ¹³⁴Cd, ^136,137In, ^139,140Sn, ^141,142Sb, ^144,145Te, ^146,147I, ^149,150Xe, ^149,150,151Cs, ^153,154Ba, and ^{154,155,156,157}La.

DOI： 10.7566/JPSJ.87.014203

Language：English   Publishing type：Research paper (scientific journal)  

A search for new proton-rich isotopes using projectile fragmentation of a 345-MeV/nucleon Xe124 beam has been performed with the BigRIPS in-flight separator at the RIKEN Nishina Center RI Beam Factory. Projectile fragments were identified by measuring the time of flight, magnetic rigidity, and energy loss in the BigRIPS separator. Projectile fragments then were transported downstream of the BigRIPS separator and re-identified by measuring the time of flight and total kinetic energy. Through such particle re-identification, we have discovered four new isotopes Mo81,82 and Ru85,86 located near the proton drip line. The Y76 and Zr78 isotopes near the proton drip line also were identified, supporting the previous report on their discovery. Furthermore, we have obtained the first clear evidence for the particle instability of Sb103. Based on the systematics of measured production yields, the upper limit values were evaluated for the half-lives of the particle-unbound isotopes Nb81,Tc85, and Sb103.

DOI： 10.1103/PhysRevC.96.034604

Language：English   Publishing type：Research paper (scientific journal)  

A new high-spin isomer in the neutron-rich nucleus ¹²⁸Cd was populated in the projectile fission of a ²³⁸U beam at the Radioactive Isotope Beam Factory at RIKEN. A half-life of T_1/2=6.3(8) ms was measured for the new state which was tentatively assigned a spin/parity of (15⁻). The experimental results are compared to shell model calculations performed using state-of-the-art realistic effective interactions and to the neighbouring nucleus ¹²⁹Cd. In the present experiment no evidence was found for the decay of a 18⁺ E6 spin-trap isomer, based on the complete alignment of the two-neutron and two-proton holes in the 0h_11/2 and the 0g_9/2 orbit, respectively, which is predicted to exist by the shell model.

DOI： 10.1016/j.physletb.2017.07.006

Language：English   Publishing type：Research paper (scientific journal)  

Excited states have been studied in Sm159, Sm161, Sm162 (Z=62), Eu163 (Z=63), and Gd164 (Z=64), populated by isomeric decay following U238 projectile fission at RIBF, RIKEN. The isomer half-lives range from 50 ns to 2.6μs. In comparison with other published data, revised interpretations are proposed for Sm159 and Eu163. The first data for excited states in Sm161 are presented, where a 2.6-μs isomer is assigned a three-quasiparticle, Kπ=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 Sm163, Eu164, and Eu165.

DOI： 10.1103/PhysRevC.96.034305

Language：English   Publishing type：Research paper (scientific journal)  

We report for the first time the β-decay scheme of Te140 (Z=52) to I140 (Z=53), with a specific focus on the Gamow-Teller strength along N=87 isotones. These results were obtained in an experiment performed at the Radioactive Ion Beam Factory (RIBF), RIKEN, where the parent nuclide, Te140, was produced through the in-flight fission of a U238 beam at 345 MeV per nucleon impinging on a Be9 target. Based on data from the high-efficiency γ-ray spectrometer, EUROBALL-RIKEN Cluster Array (EURICA), we constructed a decay scheme of I140. The half-life of Te140 has been determined to be 350(5) ms. A level at 926 keV has been assigned as a (1+) state based on the logft value of 4.89(6). This (1+) state, commonly observed in odd-odd nuclei, can be interpreted in terms of the πh11/2νh9/2 configuration formed by the Gamow-Teller transition between a neutron in the h9/2 orbital and a proton in the h11/2 orbital. We observe a sharp contrast to this type of β-decay branching to the lower-lying 1+ states between I140 and I136, where we see a large reduction as the number of neutrons increases. This is in contrast to the prediction by large-scale shell model calculations. To investigate this type of the suppression, results of the Nilsson model calculations will be discussed. Along the isotones with N=87, we discuss a characteristic feature of the Gamow-Teller distributions at 1+ states with respect to the isospin difference.

DOI： 10.1103/PhysRevC.96.014325

Language：English   Publishing type：Research paper (scientific journal)  

The level structure of the neutron-rich Cu77 nucleus is investigated through β-delayed γ-ray spectroscopy at the Radioactive Isotope Beam Factory of the RIKEN Nishina Center. Ions of Ni77 are produced by in-flight fission, separated and identified in the BigRIPS fragment separator, and implanted in the WAS3ABi silicon detector array, surrounded by Ge cluster detectors of the EURICA array. A large number of excited states in Cu77 are identified for the first time by correlating γ rays with the β decay of Ni77, and a level scheme is constructed by utilizing their coincidence relationships. The good agreement between large-scale Monte Carlo shell model calculations and experimental results allows for the evaluation of the single-particle structure near Ni78 and suggests a single-particle nature for both the 5/21- and 3/21- states in Cu77, leading to doubly magic Ni78.

DOI： 10.1103/PhysRevLett.118.242502

Language：English   Publishing type：Research paper (scientific journal)  

Neutron-rich nuclei in the vicinity of Ni78 were produced using a U238 beam at the RIKEN Radioactive Isotope Beam Factory. The particle-identification plot for the in-flight fission fragments highlights the first observation of eight new isotopes: Mn73, Fe76, Co77,78, Ni80,81,82, and Cu83. Although the β-decay half-lives of Co77 and Ni80 were recently reported by Xu [Phys. Rev. Lett. 113, 032505 (2014)]PRLTAO0031-900710.1103/PhysRevLett.113.032505 using data from the same experiment, the current work provides the first direct, quantitative evidence for the existence of these isotopes. The experimental production cross sections are reproduced in a satisfactory manner by theoretical predictions. An odd-even staggering of the cross sections was observed, and the effect appears to become more pronounced for the most exotic nuclei that were investigated. The staggering effect was interpreted as an increase of the neutron-evaporation probability for odd-N isotopes, owing to the decrease of the neutron-separation energy, Sn. The predicted cross section for Ni80 is significantly overestimated, which may be related to a weak binding of the neutron pair above the N=50 shell closure.

DOI： 10.1103/PhysRevC.95.051601

Language：English   Publishing type：Research paper (scientific journal)  

The first evidence for β-delayed proton emission from the 16⁺ spin gap isomer in ⁹⁶Cd is presented. The data were obtained from the Rare Isotope Beam Factory, at the RIKEN Nishina Center, using the BigRIPS spectrometer and the EURICA decay station. βp branching ratios for the ground state and 16⁺ isomer have been extracted along with more precise lifetimes for these states and the lifetime for the ground state decay of ⁹⁵Cd. Large scale shell model (LSSM) calculations have been performed and WKB estimates made for ℓ=0,2,4 proton emission from three resonance-like states in ⁹⁶Ag, that are populated by the β decay of the isomer, and the results compared to the new data. The calculations suggest that ℓ=2 proton emission from the resonance states, which reside ∼5 MeV above the proton separation energy, dominates the proton decay. The results highlight the importance of core-excited wavefunction components for the 16⁺ state.

DOI： 10.1016/j.physletb.2017.02.013

Language：English   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1103/PhysRevC.95.044322

Language：English   Publishing type：Research paper (scientific journal)  

Very neutron-rich Z∼60 isotopes produced by in-flight fission of a 345 MeV/nucleon U238 beam at the RI Beam Factory, RIKEN Nishina Center, have been studied by delayed γ-ray spectroscopy. New isomers were discovered in the neutron-rich N=100 isotones Sm162, Eu163, and Gd164. Half-lives, γ-ray energies, and relative intensities of these isomers were obtained. Level schemes were proposed for these nuclei and the first 2+ and 4+ states were assigned for the even-even nuclei. The first 2+ and 4+ state energies decrease as the proton numbers get smaller. The energies and the half-lives of the new isomers are very similar to those of 4- isomers known in less neutron-rich N=100 isotones Er168 and Yb170. A deformed Hartree-Fock with angular momentum projection model suggests Kπ=4- two-quasiparticle states with ν7/2[633] - ν1/2[521] configurations with similar excitation energy. The results suggest that neutron-rich N=100 nuclei are well deformed and the deformation gets larger as Z decreases to 62. The onset of K isomers with the same configuration at almost the same energy in N=100 isotones indicates that the neutron single-particle structures of neutron-rich isotones down to Z=62 do not change significantly from those of the Z=70 stable nuclei. Systematics of the excitation energies of new isomers can be explained without the predicted N=100 shell gap.

DOI： 10.1103/PhysRevC.95.034313

Language：English   Publishing type：Research paper (scientific journal)  

The β-decay half-lives of 94 neutron-rich nuclei Cs144-151, Ba146-154, La148-156, Ce150-158, Pr153-160, Nd156-162, Pm159-163, Sm160-166, Eu161-168, Gd165-170, Tb166-172, Dy169-173, Ho172-175, and two isomeric states Er174m, Dy172m 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 Ce58, Pr59, Nd60, and Sm62, and N=105 for Eu63, Gd64, Tb65, and Dy66. 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.

DOI： 10.1103/PhysRevLett.118.072701

Language：English   Publishing type：Research paper (scientific journal)  

After publication, the authors realized that one of the affiliations of I.N. Borzov was not given correctly and that a reference to his grant was missing in the acknowledgements. The correct version of the affiliations appears above and the complete text of the acknowledgements reads as follows: We thank the staff of the RIKEN Nishina Center accelerator complex for providing stable beams with high intensities for the experiment. We acknowledge the EUROBALL Owners Committee for the loan of germanium detectors and the PreSpec Collaboration for the readout electronics of the cluster detectors. This work was supported by the Spanish Ministerio de Ciencia e Innovación under contract FPA2011-29854-C04 and the Spanish Ministerio de Economía y Competitividad under contract FPA2014-57196-C5-4-P, the Generalitat Valenciana (Spain) under grant PROMETEO/2010/101, the National Research Foundation of Korea (NRF) grant funded by the Korea government (MEST) (No. NRF-2014S1A2A2028636), the Priority Centers Research Program in Korea (2009-0093817), OTKA contract number K-100835, JSPS KAKENHI (Grant No. 25247045), the Grant by IN2P3-RFBR under Agreement No. 110291054, the STFC (UK), the European Commission through the Marie Curie Actions call FP7-PEOPLE-2011-IEF under Contract No. 300096, the U.S. Department of Energy, Office of Nuclear Physics, under Contract No. DE-AC02-06CH11357, the “RIKEN foreign research program” and the German BMBF (No. 05P12RDCIA and 05P12RDNUP) and HIC for FAIR. One of the authors (INB) was supported by RFBR grant 16-02-00228.

DOI： 10.1140/epja/i2016-16375-7

Language：English   Publishing type：Research paper (scientific journal)  

The neutron-rich nuclei Nd158,160 have been studied via delayed γ-ray spectroscopy of μs isomeric states at the RIBF facility, RIKEN. These nuclei were produced following the projectile fission of a 345 AMeVU238 beam and delayed γ rays were detected by the EURICA cluster Ge array. The isomeric states have measured half-lives of 339(20) ns and 1.63(21) μs for Nd158 and Nd160, respectively. From the observed γ decays and the systematics of levels in the neighboring Nd isotopes first level schemes were constructed for these nuclei. The isomeric states of Nd158,160 have been assigned spins of (6-) and (4-), with proposed ν5/2[523]' - ν7/2[633] and ν1/2[521]' - ν7/2[633] configurations, respectively.

DOI： 10.1103/PhysRevC.94.064322

Language：English   Publishing type：Research paper (scientific journal)  

The β decay of the N = 83 nucleus ¹³¹Cd 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 1 p_{3 / 2} and 0 f_{5 / 2} proton-hole states and the energies of core-excited configurations in the semi-magic nucleus ¹³¹In. From the radiation emitted following the β decay, a level scheme of ¹³¹In was established and the β feeding to each excited state determined. Similarities between the single-particle transitions observed in the β decays of the N = 83 isotones ¹³²In and ¹³¹Cd are discussed. Finally the excitation energies of several core-excited configurations in ¹³¹In are compared to QRPA and shell-model calculations.

DOI： 10.1140/epja/i2016-16347-y

Language：English   Publishing type：Research paper (scientific journal)  

Neutron-rich ^160,161,162Sm isotopes have been populated at the RIBF, RIKEN via β decay for the first time. β-coincident γ rays were observed in all three isotopes including γ rays from the isomeric decay of ¹⁶⁰Sm and ¹⁶²Sm. The isomers in ¹⁶⁰Sm and ¹⁶²Sm have previously been observed but have been populated via β decay for the first time. The isomeric state in ¹⁶²Sm is assigned a 4^- ν7/2 ⁺[633]⊗ν1/2^-[521] configuration based on the decay pattern. The level schemes of ¹⁶⁰Sm and ¹⁶²Sm are presented. The ground states in the parent nuclei ¹⁶⁰Pm and ¹⁶²Pm are both assigned a 6^- ν7/2⁺[633] ⊗ π5/2 ^- [532] configuration based on the population of states in the daughter nuclei. Blocked BCS calculations were performed to further investigate the spin-parities of the ground states in ¹⁶⁰Pm, ¹⁶¹Pm, and ¹⁶²Pm, and the isomeric state in ¹⁶²Sm.

DOI： 10.1051/epjconf/201612302002

Language：English   Publishing type：Research paper (scientific journal)  

The β decay of the semi-magic nucleus Cd130 has been studied at the RIBF facility at the RIKEN Nishina Center. The high statistics of the present experiment allowed for a revision of the established level scheme of In130 and the observation of additional β feeding to high-lying core-excited states in In130. The experimental results are compared to shell-model calculations employing a model space consisting of the full major N=50-82 neutron and Z=28-50 proton shells and the NA-14 interaction, and good agreement is found.

DOI： 10.1103/PhysRevC.94.024303

Language：English   Publishing type：Research paper (scientific journal)  

The doubly-odd nucleus La136 is theoretically studied in terms of a large-scale shell model. The energy spectrum and transition rates are calculated and compared with the most updated experimental data. The isomerism is investigated for the first 14+ state, which was found to be an isomer in the previous study [Phys. Rev. C 91, 054305 (2015)PRVCAN0556-281310.1103/PhysRevC.91.054305]. It is found that the 14+ state becomes an isomer due to a band crossing of two bands with completely different configurations. The yrast band with the (νh11/2-1- πh11/2) configuration is investigated, revealing a staggering nature in M1 transition rates.

DOI： 10.1103/PhysRevC.94.014317

Language：English   Publishing type：Research paper (scientific journal)  

We report on a new measurement of the g factor of the (13/2+) isomeric state in the neutron-rich nucleus Cu69. This study demonstrates the possibility of obtaining considerable nuclear spin alignment for multi-quasiparticle states in single-nucleon removal reactions. The time-dependent perturbed angular distribution (TDPAD) method was used to extract the gyromagnetic factor of the (13/2+) [T1/2=351(14) ns] isomeric state of Cu69. Its g factor was obtained as g(13/2+)=0.248(9). The experimentally observed spin alignment for the state of interest was deduced as A=-3.3(9)%.

DOI： 10.1103/PhysRevC.93.054313

Language：English   Publishing type：Research paper (scientific journal)  

For the first time, the γ decay of excited states has been observed in a nucleus situated in the quadrant south-east of doubly magic Sn132, a region in which experimental information so far is limited to ground-state properties. Six γ rays with energies of 50, 86, 103, 227, 357, and 602 keV were observed following the β-delayed neutron emission from Cd85133, populated in the projectile fission of a U238 beam at the Radioactive Isotope Beam Factory at RIKEN within the EURICA project. The new experimental information is compared to the results of a modern realistic shell-model calculation, the first one in this region very far from stability, focusing in particular on the π0g9/2-1 - ν1f7/2 particle-hole multiplet in In83132. In addition, theoretical estimates based on a scaling of the two-body matrix elements for the πh11/2-1 - νg9/2 analog multiplet in Tl127208, one major proton and one major neutron shell above, are presented.

DOI： 10.1103/PhysRevC.93.041301

Language：English   Publishing type：Research paper (scientific journal)  

The level structure of the ⁷⁷Cu nucleus has been studied by means of β-delayed γ-ray spectroscopy at RIKEN Nishina Center. Secondary beam particles in the region near ⁷⁸Ni were produced via in-flight fission of ²³⁸U on a thick ⁹Be target at a primary beam energy of 345 MeV/nucleon. After identification in atomic number (Z) and mass-to-charge ratio (A/Q) in the BigRIPS fragment separator, the fission products were delivered to the final focal plane through the ZeroDegree Spectrometer. The WAS3ABI silicon stack array was used for the implantation of the ions, while de-excitation γ rays were detected with the EURICA γ-ray spectrometer at the focal plane. Beta-correlated particle identification of ⁷⁷Ni allowed to obtain the γ-ray spectrum of the daughter ⁷⁷Cu in a selective way. Experimental details and first results on the excited states in ⁷⁷Cu nucleus will be presented in this contribution.

DOI： 10.5506/APhysPolB.47.889

Language：English   Publishing type：Research paper (scientific journal)  

The decay of a new four-quasiparticle isomeric state in ¹⁶⁰Sm has been observed using γ-ray spectroscopy at the RIBF, RIKEN. The four-quasiparticle state is assigned a 2π⊗2ν π5/2^-[532], π5/2⁺[413], ν5/2^-[523], ν7/2⁺[633] configuration. The half-life of this (11⁺) state is measured to be 1.8(4) μs. The (11⁺) isomer decays into a rotational band structure, based on a (6^-) ν5/2^-[523]⊗ν7/2⁺[633] bandhead, consistent with the g_K-g_R values. This decays to a (5^-) two-proton quasiparticle state, which in turn decays to the ground state band. Potential energy surface and blocked-BCS calculations were performed in the deformed midshell region around ¹⁶⁰Sm. They reveal a significant influence from β₆ deformation and that ¹⁶⁰Sm is the best candidate for the lightest four-quasiparticle K isomer to exist in this region. The relationship between reduced hindrance and isomer excitation energy for E1 transitions from multiquasiparticle states is considered with the new data from ¹⁶⁰Sm. The E1 data are found to agree with the existing relationship for E2 transitions.

DOI： 10.1016/j.physletb.2015.12.026

Language：English   Publishing type：Research paper (scientific journal)  

A β-decay spectroscopy experiment around ¹⁵⁸Nd was performed at RI Beam Factory (RIBF), RIKEN Nishina Center, in order to understand the production mechanism of the A≈165 rare-earth element (REE) peak in the r-process mass abundance pattern. In this experiment, 53 half-lives are measured including 34 new results, which could be employed in a fully dynamic r-process network calculation.

DOI： 10.1051/epjconf/201610908003

Language：English   Publishing type：Research paper (scientific journal)  

In this article we report on the first spectroscopic information on Sb8951140 and the observation of an isomer in this nucleus with T1/2=41(8) μs. It is located in close proximity to Sn140 for N=90, where the νf7/2 orbit is completely filled. The possible origin of the isomeric state is a πg7/21×νf7/2-1 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.

DOI： 10.1103/PhysRevC.93.014316

Language：English   Publishing type：Research paper (scientific journal)  

A new isomer with ms half-life was observed in ¹⁶⁰Nd at RIBF, RIKEN Nishina Center by using in-flight fission of a ²³⁸U beam and a cluster-type Ge detector array EURICA. The experimental results and a PSM calculation indicate that the isomer in ¹⁶⁰Nd is a 2 quasi-particle excitation of neutrons with a configuration of v1/2[521] × v7/2[633] as the case in other N = 100 isotones. The E(4⁺)/E(2⁺) ratio of the ground-state band, 3.29, shows the ¹⁶⁰Nd is well deformed and the ground band has a rotational nature. The 4^- excitation of Nd showed an increase in energy by ∼100 keV compared to that of ¹⁶²Sm as predicted by the PSM calculation. A PSM calculation was performed by changing input β₄ value and confirmed that the large hexadecupole deformation in Nd was responsible for the increase of the isomer energy.

Language：English   Publishing type：Research paper (scientific journal)  

The first fast-timing measurements from nuclides produced via the in-flight fission mechanism are reported. The lifetimes of the first 2⁺ states in ^104,106Zr nuclei have been measured via β-delayed γ-ray timing of stopped radioactive isotope beams. An improved precision for the lifetime of the 21+ state in ¹⁰⁴Zr was obtained, τ(21+)=2.90-20+25 ns, as well as a first measurement of the 21+ state in ¹⁰⁶Zr, τ(21+)=2.60-15+20 ns, with corresponding reduced transition probabilities of B(E2;21+→0g.s.+)=0.39(2) e2b2 and 0.31(1) e²b², respectively. Comparisons of the extracted ground-state deformations, β₂=0.39(1) (¹⁰⁴Zr) and β₂=0.36(1) (¹⁰⁶Zr) with model calculations indicate a persistence of prolate deformation. The data show that ¹⁰⁴Zr is the most deformed of the neutron-rich Zr isotopes measured so far.

DOI： 10.1016/j.physletb.2015.09.043

Language：English   Publishing type：Research paper (scientific journal)  

In the EURICA campaign aimed at exploration of the Ni78 region, an isomeric state of Co76 has been observed via γ-ray spectroscopy. The nuclei were produced by in-flight fission of a U238 beam at the Radioactive Isotope-Beam Factory. Two coincident γ rays of 192.02(30) and 446.4(7) keV from the decay of a t1/2=2.96(2529)μs isomeric state of Co76 have been observed. The decay of the isomer was assigned to an E1 transition with a reduced transition probability of B(E1;3+→2-)=1.79(16)×10-8 W.u. A β-decaying state with spin-parity 1- and a half-life of 16(4) ms was also observed in the data, and the known state with a half-life of 22(57) ms was assigned to have a spin-parity of 8-. Furthermore, the isomer of Ni76 has been remeasured to 547.8(33) ns giving a B(E2;8+→6+) value of 0.786(5) W.u. A new excited state at 2994.6(5) keV, decaying via a γ ray of 2004.5(4) keV, has also been observed. This is in agreement with either of the predicted 02+ or 22+ states. These results are discussed in terms of the shell model and the interaction of the νp1/2 and πf7/2 orbitals.

DOI： 10.1103/PhysRevC.92.051305

Language：English   Publishing type：Research paper (scientific journal)  

We report on the first β-decay data of Sb138 to Te138 isotopes beyond the doubly magic Sn132. The parent nucleus was produced by the in-flight fission of a U238 beam on a Be9 target at 345 MeV per nucleon and measured at the BigRIPS separator of the Radioactive Isotope Beam Factory at RIKEN. By using advanced β-γ spectroscopy techniques, the half-life and the tentative spin-parity of Sb138 were measured to be 346(19) ms and (3-), respectively. In addition, we observed several low-lying non-yrast states in Te138 for the first time. Our data allowed us to rearrange the positions of the first 2+ and 4+ states in this nucleus and to construct the level scheme of Te138 in accordance with shell-model calculations. Additionally, we extend energy systematics of Te isotopes within neutron numbers 54 and 86.

DOI： 10.1103/PhysRevC.92.044320

Language：English   Publishing type：Research paper (scientific journal)  

Absolute cross sections for isotopically identified products formed in multinucleon transfer in the Xe136+Pt198 system at ∼8MeV/nucleon are reported. The isotopic distributions obtained using a large acceptance spectrometer demonstrated the production of the "hard-to-reach" neutron-rich isotopes for Z<78 around the N=126 shell closure far from stability. The main contribution to the formation of these exotic nuclei is shown to arise in collisions with a small kinetic energy dissipation. The present experimental finding corroborates for the first time recent predictions that multinucleon transfer reactions would be the optimum method to populate and characterize neutron-rich isotopes around N=126 which are crucial for understanding both astrophysically relevant processes and the evolution of "magic" numbers far from stability.

DOI： 10.1103/PhysRevLett.115.172503

Language：English   Publishing type：Research paper (scientific journal)  

We report new data on the Sb1366- yrast isomer with T1/2=489(40) ns and πg7/21×νf7/23 configuration, populated in the projectile fission of U238 on a Be9 target. The analysis confirms the lifetime, providing a good accuracy measurement. In addition, the decay of the isomer to the ground state is newly suggested. Our result for the isomeric decay scheme is in a good agreement with shell-model calculations.

DOI： 10.1103/PhysRevC.92.024304

Language：English   Publishing type：Research paper (other academic)  

A decay spectroscopy experiment was performed within the EURICA campaign at RIKEN in 2012. It aimed at the isomer and particle spectroscopy of excited states and ground states in the mass region below the doubly magic ¹⁰⁰Sn. The N = Z nuclei ⁹⁸In, ⁹⁶Cd and ⁹⁴Ag were of particular interest for the present study. Preliminary results on the neutron deficient nuclei ⁹³Ag and ⁹⁴Ag are presented. In ⁹⁴Ag a more precise value for the half-life of the ground state's superallowed Fermi transition was deduced. In addition the energy spectra of the mentioned decay could be reproduced through precise Geant4 simulations of the used active stopper SIMBA. This will enable us to extract Q_β values from the measured data. The decay of ⁹³Ag is discussed based on the observed implantation-decay correlation events. Owned by the authors, published by EDP Sciences, 2015.

DOI： 10.1051/epjconf/20159301024

Language：English   Publishing type：Research paper (scientific journal)  

The β-decay half-lives of 110 neutron-rich isotopes of the elements from ₃₇Rb to ₅₀Sn were measured at the Radioactive Isotope Beam Factory. The 40 new half-lives follow robust systematics and highlight the persistence of shell effects. The new data have direct implications for r-process calculations and reinforce the notion that the second (A ≈ 130) and the rare-earth-element (A ≈ 160) abundance peaks may result from the freeze-out of an (n, γ) ⇄ (γ,n) equilibrium. In such an equilibrium, the new half-lives are important factors determining the abundance of rare-earth elements, and allow for a more reliable discussion of the r process universality. It is anticipated that universality may not extend to the elements Sn, Sb, I, and Cs, making the detection of these elements in metal-poor stars of the utmost importance to determine the exact conditions of individual r-process events.

DOI： 10.1103/PhysRevLett.114.192501

Language：English   Publishing type：Research paper (scientific journal)  

The β decay of Cd¹²⁹, produced in the relativistic fission of a U²³⁸ beam, was experimentally studied at the RIBF facility at the RIKEN Nishina Center. From the γ radiation emitted after the β decays, a level scheme of In¹²⁹ was established comprising 31 excited states and 69 γ-ray transitions. The experimentally determined level energies are compared to state-of-the-art shell-model calculations. The half-lives of the two β-decaying states in Cd¹²⁹ were deduced and the β feeding to excited states in In¹²⁹ were analyzed. It is found that, as in most cases in the Z<50, N≤82 region, both decays are dominated by the ν0g_7/2→π0g_9/2 Gamow-Teller transition, although the contribution of first-forbidden transitions cannot be neglected.

DOI： 10.1103/PhysRevC.91.054324

Language：English   Publishing type：Research paper (scientific journal)  

The half-lives of 2⁺₁ states were measured for ^102,104Zr and ^106,108Mo to test a new implementation of a LaBr₃(Ce) array at the RIBF, RIKEN, Japan. The nuclei of interest were produced through the fission of a 345 MeV/nucleon ²³⁸U beam and selected by the BigRIPS separator. Fission fragments were implanted into the WAS3ABi active stopper, surrounding which, 18 LaBr₃(Ce) detectors provided fast γ-ray detection. Timing between the LaBr₃(Ce) array and plastic scintillators allowed for the measurement of half-lives of low-lying states. The preliminary results, which agree with literature values, are presented along with experimental details.

DOI： 10.5506/APhysPolB.46.721

Language：English   Publishing type：Research paper (scientific journal)  

Excited states in the N=102 isotones Gd166 and Sm164 have been observed following isomeric decay for the first time at RIBF, RIKEN. The half-lives of the isomeric states have been measured to be 950(60) and 600(140) ns for Gd166 and Sm164, respectively. Based on the decay patterns and potential energy surface calculations, including β6 deformation, a spin and parity of 6- has been assigned to the isomeric states in both nuclei. Collective observables are discussed in light of the systematics of the region, giving insight into nuclear shape evolution. The decrease in the ground-band energies of Gd166 and Sm164 (N=102) compared to Gd164 and Sm162 (N=100), respectively, presents evidence for the predicted deformed shell closure at N=100.

DOI： 10.1103/PhysRevLett.113.262502

Language：English   Publishing type：Research paper (scientific journal)  

The decay of an isomeric state in the neutron-rich nucleus ¹²⁹Cd has been observed via the detection of internal conversion and Compton electrons providing first experimental information on excited states in this nucleus. The isomer was populated in the projectile fission of a ²³⁸U beam at the Radioactive Isotope Beam Factory at RIKEN. From the measured yields of γ-rays and internal conversion electrons, a multipolarity of E3 was tentatively assigned to the isomeric transition. A half-life of T_1/2=3.6(2)ms was determined for the new state which was assigned a spin of (21/2⁺), based on a comparison to shell model calculations performed using state-of-the-art realistic effective interactions.

DOI： 10.1016/j.physletb.2014.09.047

Language：English   Publishing type：Research paper (scientific journal)  

Delayed γ-ray cascades, originating from the decay of (6+) isomeric states, in the very neutron-rich, semimagic isotopes 136,138Sn have been observed following the projectile fission of a 238U beam at RIBF, RIKEN. The wave functions of these isomeric states are proposed to be predominantly a fully aligned pair of f7/2 neutrons. Shell-model calculations, performed using a realistic effective interaction, reproduce well the energies of the excited states of these nuclei and the measured transition rates, with the exception of the B(E2;6+→4+) rate of 136Sn, which deviates from a simple seniority scheme. Empirically reducing the νf7/22 orbit matrix elements produces a 41+ state with almost equal seniority 2 and 4 components, correctly reproducing the experimental B(E2;6+→4+) rate of 136Sn. These data provide a key benchmark for shell-model interactions far from stability.

DOI： 10.1103/PhysRevLett.113.132502

Language：English   Publishing type：Research paper (scientific journal)  

The half-lives of 20 neutron-rich nuclei with Z=27-30 have been measured at the RIBF, including five new half-lives of Co76(21.7-4.9+6.5ms), Co77(13.0-4.3+7.2ms), Ni79(43.0-7.5+8.6ms), Ni80(23.9-17.2+26.0ms), and Cu81(73.2±6.8ms). In addition, the half-lives of Co73-75, Ni74-78, Cu78-80, and Zn80-82 were determined with higher precision than previous works. Based on these new results, a systematic study of the β-decay half-lives has been carried out, which suggests a sizable magicity for both the proton number Z=28 and the neutron number N=50 in Ni78.

DOI： 10.1103/PhysRevLett.113.032505

Language：English   Publishing type：Research paper (scientific journal)  

A new isomer with a half-life of 23.0(8) ms has been identified at 2406 keV in Pd126 and is proposed to have a spin and parity of 10+ with a maximally aligned configuration comprising two neutron holes in the 1h11/2 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 Ag126. The smaller energy difference between the 10+ and 7- isomers in Pd126 than in the heavier N=80 isotones can be interpreted as being ascribed to the monopole shift of the 1h11/2 neutron orbit. The effects of the monopole interaction on the evolution of single-neutron energies below Sn132 are discussed in terms of the central and tensor forces.

DOI： 10.1103/PhysRevLett.113.042502

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1103/PhysRevLett.113.049902

Language：English   Publishing type：Research paper (scientific journal)  

A low-lying state in In82131, the one-proton hole nucleus with respect to double magic Sn132, was observed by its γ decay to the Iπ=1/2- β-emitting isomer. We identify the new state at an excitation energy of Ex=1353keV, which was populated both in the β decay of Cd13183 and after β-delayed neutron emission from Cd13284, as the previously unknown πp3/2 single-hole state with respect to the Sn132 core. Exploiting this crucial new experimental information, shell-model calculations were performed to study the structure of experimentally inaccessible N=82 isotones below Sn132. The results evidence a surprising absence of proton subshell closures along the chain of N=82 isotones. The consequences of this finding for the evolution of the N=82 shell gap along the r-process path are discussed.

DOI： 10.1103/PhysRevLett.112.132501

Language：English   Publishing type：Research paper (scientific journal)  

The feasibility of the multi-nucleon transfer (MNT) reaction in the ¹³⁶Xe +¹⁹⁸Pt system was investigated for synthesizing neutron-rich heavy nuclei around mass number A∼200 of astrophysical interest. Identification of the projectile-like fragments (PLF's) was successfully performed by using VAMOS++ spectrometer. The isotopic distributions of the PLF's produced by two-proton stripping and pickup reactions were compared with each other, demonstrating the properties of the MNT reactions observed in the present system. The two-proton pickup channels strongly populated than the twoproton stripping channels were observed. The isotopic distributions for different total kinetic energy loss (TKEL) ranges are also discussed. The overall enhancement of the strength of the two-proton pickup compared with the two-proton stripping appears to be related to the MNT reactions with relatively moderate energy dissipation.

DOI： 10.1051/epjconf/20146603044

Language：English   Publishing type：Research paper (scientific journal)  

The first EURICA campaign with high intensity Uranium beams took place at RIKEN in November/December 2012. Within this campaign experiment NP1112-RIBF85 was performed dedicated to the study of the isomeric and beta decays of neutronrich Cd, In, Sn and Sb isotopes towards and beyond the N=82 neutron shell closure. In this contribution we present a first status report of the analysis of the extensive data set obtained in this experiment.

DOI： 10.1051/epjconf/20146602040

Language：English   Publishing type：Research paper (scientific journal)  

A large fraction of the rare-earth elements around A = 160 observed in the solar system are produced in the astrophysical rapid (r-) neutron-capture process. However, current stellar models cannot completely explain the relative abundance of these elements partially because of nuclear physics uncertainties. To address this problem, a β-decay spectroscopy experiment was performed at RI Beam Factory (RIKEN), aimed at studying a wide range of very neutron-rich nuclei with Z ∼ 60. This experiment provides a test of nuclear models as well as experimental inputs for r-process calculations.

Language：English   Publishing type：Research paper (scientific journal)  

Spin-polarized radioactive nuclear beams at TRIUMF enable a new spectroscopic method which efficiently assigns spins and parities of the daughter levels by taking advantage of the asymmetric β-decay of the polarized parent nucleus. This method was successfully applied to structure studies of ²⁹Mg and ³⁰Mg in connection with the physics of the "island of inversion". In ²⁹Mg, two low-lying levels with intruder configuration were assigned. In ³⁰Mg, coexistence of spherical shape, prolate shape and γ-collectivity was strongly suggested.

DOI： 10.1007/s10751-013-0895-5

Language：English  

Spin-polarized radioactive nuclear beams at TRIUMF enable a new spectroscopic method which efficiently assigns spins and parities of the daughter levels by taking advantage of the asymmetric β-decay of the polarized parent nucleus. This method was successfully applied to structure studies of ²⁹Mg and ³⁰Mg in connection with the physics of the “island of inversion”. In ²⁹Mg, two low-lying levels with intruder configuration were assigned. In ³⁰Mg, coexistence of spherical shape, prolate shape and γ-collectivity was strongly suggested.

DOI： 10.1007/978-94-007-7963-1_20

Language：English   Publishing type：Research paper (scientific journal)  

The first EURICA campaign with high intensity Uranium beams took place at RIKEN in November/December 2012. Within this campaign experiment NP1112-RIBF85 was performed dedicated to the study of the isomeric and beta decays of neutron-rich Cd, In, Sn and Sb isotopes towards and beyond the N=82 neutron shell closure. In this contribution we will first provide information about the status of the analysis of the extensive data set obtained in this experiment and close with a short outlook.

DOI： 10.1088/1742-6596/533/1/012045

Language：English   Publishing type：Research paper (other academic)  

EURICA is a project at the RIKEN Nishina Center aimed at studying a wide range of exotic nuclei through β-decay measurements and high-resolution γ-ray spectroscopy. During its first two years of operation, about 80 days of beam time have been dedicated to the project allowing the exploration of several very exotic regions of the nuclear chart, which include key nuclei such as 78Ni, 100Sn, 110Zr, 128Pd, and 138Sn. Data analysis of the EURICA experiments is currently ongoing.

DOI： 10.1063/1.4874097

Language：English   Publishing type：Research paper (other academic)  

A large fraction of the rare-earth elements observed in the solar system is produced in the astrophysical rapid neutron capture process (r-process). However, current stellar models cannot completely explain the relative abundance of these elements partially because of nuclear physics uncertainties. To address this problem, a β-decay spectroscopy experiment was performed at RI Beam Factory (RIBF) at RIKEN, aimed at studying a wide range of very neutron-rich nuclei with Z∼60 that are progenitors of the rare-earth elements with mass number A∼460. The experiment provides a test of nuclear models as well as experimental inputs for r-process calculations. This contribution presents the experimental setup and some preliminary results of the experiment.

DOI： 10.1063/1.4874099

Language：English   Publishing type：Research paper (scientific journal)  

EURICA is a project at RIKEN Nishina Center aimed at studying a wide range of exotic nuclei through β-decay measurements and high-resolution γ-ray spectroscopy. The setup is located behind the BigRIPS fragment separator and the ZeroDegree spectrometer at the RIBF. EURICA consists of the HPGe cluster detectors from the previous Euroball and RISING projects, together with double-sided silicon-strip detectors for β-decay counting and lifetime measurements. In total, this setup provides us with the possibility to study several aspects of the exotic nuclei produced at the RIBF.

DOI： 10.1016/j.nimb.2013.03.018

Language：English   Publishing type：Research paper (scientific journal)  

Multinucleon transfer reactions between two heavy ions are an important tool for production and investigation of exotic neutron-rich nuclei, which are difficult to access by other methods. The ¹³⁶Xe + ¹⁹⁸Pt system is a candidate to efficiently produce neutron-rich nuclei around the neutron magic number N=126 for the KEK isotope separation project. In order to confirm this, measurements of the production cross sections with the large acceptance magnetic spectrometer VAMOS++ and de-excitation gamma rays from target-like fragments using the high efficiency germanium array EXOGAM at GANIL are reported. The measured isotopic distributions of the projectile-like fragments are compared with GRAZING calculations. The proton stripping channels show rough agreements between measurements and calculations. For the proton pick-up channels, the measured distributions are shifted toward the heavier masses and show enhanced cross sections in transfers of two or more protons.

DOI： 10.1016/j.nimb.2013.04.036

Language：English   Publishing type：Research paper (scientific journal)  

We have measured the production rates and production cross sections for a variety of radioactive isotopes which were produced from ¹²⁴Xe, ⁴⁸Ca, and ²³⁸U beams at an energy of 345 MeV/nucleon using the BigRIPS separator at the RIKEN Nishina Center RI Beam Factory (RIBF). Proton-rich isotopes with atomic numbers Z = 40-52 and neutron-rich isotopes with Z = 5-16 were produced by projectile fragmentation of the ¹²⁴Xe and ⁴⁸Ca beam on Be targets, respectively. Neutron-rich isotopes with Z = 20-59 were produced by in-flight fission of the ²³⁸U beam, in which both Be and Pb were used as production targets. The measured production rates and production cross sections were compared with those of the LISE ⁺⁺ calculations, and overall fairly good agreement has been obtained. Furthermore, in the measurements with the ¹²⁴Xe beam, we have discovered four new isotopes on the proton-drip line, ^85,86Ru and ^81,82Mo, and obtained the clear evidence that ¹⁰³Sb is particle unbound with an upper limit of 49 ns for the half-life. The measurements of projectile-fragment momentum distributions have been also performed with the ¹²⁴Xe beam, in which the low-momentum tails of the distributions have been measured for the first time at the energy of 345 MeV/nucleon.

DOI： 10.1016/j.nimb.2013.08.049

Language：English   Publishing type：Research paper (scientific journal)  

The level structures of the very neutron-rich nuclei Pd128 and Pd126 have been investigated for the first time. In the r-process waiting-point nucleus Pd128, a new isomer with a half-life of 5.8(8) μs is proposed to have a spin and parity of 8⁺ and is associated with a maximally aligned configuration arising from the g_9/2 proton subshell with seniority υ=2. For Pd126, two new isomers have been identified with half-lives of 0.33(4) and 0.44(3) μs. The yrast 2⁺ energy is much higher in Pd128 than in Pd126, while the level sequence below the 8⁺ isomer in Pd128 is similar to that in the N=82 isotone Cd130. The electric quadrupole transition that depopulates the 8⁺ isomer in Pd128 is more hindered than the corresponding transition in Cd130, as expected in the seniority scheme for a semimagic, spherical nucleus. These experimental findings indicate that the shell closure at the neutron number N=82 is fairly robust in the neutron-rich Pd isotopes.

DOI： 10.1103/PhysRevLett.111.152501

Language：English   Publishing type：Research paper (scientific journal)  

The 135La nucleus has been studied using the fusion-evaporation reaction 124Sn(17N,6n) induced by the 17N radioactive beam. The level scheme has been constructed from the γ-γ coincidence measurement with an array of 12 HPGe detectors, and the lifetimes of two previously known isomeric states has been deduced. The transitions and their intensities observed in the current work as well as the level scheme derived from them is in agreement with the results of a recently published work. However, our interpretation of the results differs significantly in terms of spin and parity assignments, thus solving various contradictions concerning the configurations of some of the bands discussed in the aforementioned work.

DOI： 10.1103/PhysRevC.88.044309

Language：English   Publishing type：Research paper (scientific journal)  

116Ru and 118Ru have been studied via β-delayed γ-ray spectroscopy of nuclei produced in fragmentation reactions at the Radioactive Ion-Beam Factory (RIBF) facility. Level schemes with positive-parity states up to spin J=6 have been constructed. The results have been discussed in terms of the interacting boson model, the algebraic collective model, and total Routhian surfaces. We conclude that the very neutron-rich nuclei still show many features associated with triaxial γ-soft nuclei, represented by the O(6) symmetry, but are approaching a spherical structure, the U(5) symmetry, with increasing neutron number towards the N=82 shell closure. In 118Ru, hints of a shape transition in the ground state have been observed.

DOI： 10.1103/PhysRevC.88.024301

Language：English   Publishing type：Research paper (scientific journal)  

We have been studying the structure of Mg isotopes in the region of the N = 20 island of inversion, to clarify the structure change as a function of the neutron number. The experiments are being performed by our unique method of β-decay spectroscopy taking advantage of highly-spin-polarized radioactive nuclear beams at TRIUMF. The β-decay asymmetry in the Na-isotope decay enables unambiguous spin-parity assignments of the levels in the daughter Mg isotope, and it becomes possible to compare the experimental data and theoretical predictions on a level-by-level basis. The present paper reports on the results of the β decay of 30Na→30Mg. From the detailed decay scheme of 30Na, it is suggested that the 30Mg levels at 1.788 MeV [(0+2 )], 3.460 MeV [(2)+], 4.967 MeV [1+], and 5.414 MeV [2+] have deformed shapes with intruder configurations, whereas the level at 2.466 MeV [(2+2 )] has different nature both from the spherical ground state and the deformed four levels. It is proposed that the 2+2 level is the band-head of the predicted γ-band.

Event date： 2021.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

Event date： 2021.3

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Venue：Beppu   Country：Japan  

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Event date： 2019.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：佐賀大学   Country：Japan