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Structure of the neutron-rich nucleus $^{30}\mathrm{Mg}$, which is located close to the region of the $N=20$ ``island of inversion,'' has been investigated by $\ensuremath{\beta}\text{\ensuremath{-}}\ensuremath{\gamma}$ spectroscopy of spin-polarized $^{30}\mathrm{Na}$. From the detailed $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ coincidence relations, nine new states have been established in $^{30}\mathrm{Mg}$. The spin-polarization of $^{30}\mathrm{Na}$ enabled firm spin-parity assignments for seven states in $^{30}\mathrm{Mg}$ by means of the spatial asymmetry of $\ensuremath{\beta}$-ray counts in coincidence with the $^{30}\mathrm{Mg}\phantom{\rule{4pt}{0ex}}\ensuremath{\gamma}$ rays. Based on the experimental information, it is shown that various characteristic structures coexist in $^{30}\mathrm{Mg}$: (i) the ground-state vibrational-like band, (ii) the deformed band built on the ${0}_{2}^{+}$ state at 1.788 MeV, (iii) the $\ensuremath{\gamma}$-vibrational band built on the ${2}_{3}^{+}$ state at 3.543 MeV, and (iv) four states around 5 MeV associated with large $\ensuremath{\beta}$-transition probabilities: ${1}^{+}$ and ${2}^{+}$ states with spherical nature, ${1}^{+}$ and ${2}^{+}$ states with collective nature. The experimental results are compared with three theoretical calculations of the CHFB $+$ LQRPA, the AMD $+$ GCM, and the large-scale shell model with the EEdf1 interaction. All these theories reasonably reproduce the three bands.

In-flight fission of a 345 MeV per nucleon 238U primary beam on a 2 mm thick 9Be target has been used to produce and study the decays of a range of neutron-rich nuclei centred around the doubly mid-shell nucleus 170Dy at the RIBF Facility, RIKEN, Japan. The produced secondary fragments of interest were identified eventby- event using the BigRIPS separator. The fragments were implanted into the WAS3ABI position sensitive silicon active stopper which allowed pixelated correlations between implants and their subsequent β-decay. Discrete γ-ray transitions emitted following decays from either metastable states or excited states populated following beta decay were identified using the 84 coaxial high-purity germanium (HPGe) detectors of the EURICA spectrometer, which was complemented by 18 additional cerium-doped lanthanum bromide (LaBr3)

The structure of excited states in the neutron-rich nucleus 31 Mg, which is in the region of the “island of inversion” associated with the neutron magic number N = 20 , is studied by β – γ spectroscopy of spin-polarized 31 Na. Among the 31 Mg levels below the one neutron separation energy of 2.3 MeV, the spin values of all five positive-parity levels are unambiguously determined by observing the anisotropic β decay. Two rotational bands with K π = 1 / 2 + and 1 / 2 − are proposed based on the spins and energies of the levels. Comparison on a level-by-level basis is performed between the experimental results and theoretical calculations by the antisymmetrized molecular dynamics (AMD) plus generator coordinate method (GCM). It is found that various nuclear structures coexist in the low excitation energy region in 31 Mg.

the beta-decay half-lives of 94 neutron-rich nuclei 144-151Cs; 146-155Ba; 148-156La; 150-158Ce; 153-160Pr; 156-162Nd; 159-163Pm; 160-166Sm; 161-168eu; 165-170Gd, 166-172Tb; 169-173Dy; 172-175Ho, and 2 isomeric states 174mEr and 172mDy were measured at the Radioactive Isotope Beam Factory providing a new experimental basis to test theoetical models. Strikingl large drops of beta-decay half-lives are observed at neutron-number N=97 for Ce, Pr, Nd and Sm and N=105 for eu, Gd, Tb and Dy.

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.

© The Authors, published by EDP Sciences, 2017. This short paper presents the identification of a metastable, isomeric-state decay in the neutron-rich odd-odd, prolate-deformed nucleus 166Tb. The nucleus of interest was formed using the in-flight fission of a 345 MeV per nucleon 238U primary beam at the RIBF facility, RIKEN, Japan. Gamma-ray transitions decaying from the observed isomeric states in 166Tb were identified using the EURICA gamma-ray spectrometer, positioned at the final focus of the BigRIPS fragments separator. The current work identifies a single discrete gamma-ray transition of energy 119 keV which de-excites an isomeric state in 166Tb with a measured half-life of 3.5(4) μs. The multipolarity assignment for this transition is an electric dipole and is made on the basis internal conversion and decay lifetime arguments. Possible two quasi-particle Nilsson configurations for the initial and final states which are linked by this transition in 166Tb are made on the basis of comparison with Blocked BCS Nilsson calculations, with the predicted ground state configuration for this nucleus arising from the coupling of the v(1-/2)[521] and π(3+/2) Nilsson orbitals. ispartof: EPJ Web of Conferences vol:146 ispartof: ND 2016: International Conference on Nuclear Data for Science and Technology location:Bruges, Belgium date:11 Sep - 16 Sep 2016 status: Published online

In this contribution the low-excitation structural properties of the doubly mid-shell nucleus 170Dy 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.

We present information on the excited states in the prolate-deformed, neutron-rich nuclei 165;167Tb100;102. The nuclei of interest were synthesised following in-flight fission of a 345 MeV per nucleon 238U primary beam on a 2 mm 9Be 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 s regime measured using the EURICA gamma-ray spectrometer. Metastable-state decays are identified in 165Tb and 167Tb and interpreted as arising from hindered E1 decay from the 7 2 [523] single quasi-proton Nilsson configuration to rotational states built on the 3 2 [411] single quasi-proton ground state. 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 170Dy doubly-midshell nucleus is approached.

Physics letters / B 760, 641 - 646 (2016). doi:10.1016/j.physletb.2016.07.057, Published by North-Holland Publ., Amsterdam