Isomeric levels in92Rb and the structure of neutron-rich92,94Rb isotopes (original) (raw)

Medium-spin states of the neutron-rich87,89Br isotopes: configurations and shapes

Journal of Physics: Conference Series, 2016

Medium-spin excited states of the neutron-rich 87 Br and 89 Br nuclei were observed and studied for the first time. They were populated in fission of 235 U induced by the coldneutron beam of the PF1B facility of the Institut Laue-Langevin, Grenoble. The measurement of γ radiation following fission has been performed using the EXILL array of Ge detectors. The observed level schemes were compared with results of large valence space shell model calculations. Both medium-spin level schemes consist of band-like structures, which can be understood as bands built on the πf 5/2 , πp 3/2 and πg 9/2 configurations. Both nuclei have 5/2 − ground state spin-parity contrary to the odd-mass Br isotopes containing fewer neutrons, which have 3/2 − ground state spin-parity. On the basis of the properties of the πg 9/2 decoupled bands the deformations of the 87 Br and 89 Br fit to the systematics of nuclei in the region. 87 Br is close to the vibrational limit, while 89 Br is more rotational.

Structure of Kr90,91 nuclei: Solving the puzzle of their population in fission

Physical Review C

Excited states of 90,91 Kr nuclei have been populated following the cold-neutron-induced fission of a 235 U target. The γ rays emitted following fission reactions were measured using the highly efficient array of high-purity Ge detectors, EXILL, at the Institute-Laue-Langevin, Grenoble. The surprisingly low population of 91 Kr reported in the spontaneous fission of 252 Cf measurement has been explained and new level schemes of 90,91 Kr nuclei were established. Moderate γ collectivity is observed in both nuclei. Large-scale shell-model calculations support the experimental picture of the Z = 36, Kr isotopes forming a border line between lower-Z nuclei showing moderate γ collectivity and the heavier-Z nuclei, where distinct shape changes are observed.

Structure of the neutron-rich nucleus 37 94 rb57

Zeitschrift f�r Physik A: Atomic Nuclei, 1989

A level scheme has been established for 94Rb57 based on studies at the fission-product separator JOSEF of 7-7 coincidences following the/~-decay of 94Kr. For the 190.7 keV level a half-life of 2.5(8) ns has been determined through the centroid-shift method. The major /%decay branch of 94Kr proceeds with log ft=3.7 into the 988.4 keV state in 94Rb. This transition must be of the 0+~ 1 + GT type involving the transition vgT/2-~7Cgg/2. IBFFM calculations have been performed for 94Rb, starting from the parametrization used in the previous IBM investigations for the isotope 93Rb and the isotone 96y. A theoretical interpretation of the low-lying levels including propositions for the spins is given in a comparison to the available data.

Near-yrast, medium-spin, excited states ofRb91,Rb93, andRb95

Physical Review C, 2010

The medium-spin structure of the nuclei 93 Rb and 95 Rb is studied following the neutron-induced fission of 235 U at the PF1B neutron guide, using the FIFI spectrometer, and at the Lohengrin mass spectrometer of the Institut Laue-Langevin Grenoble. These nuclei, plus 91 Rb, are also studied following the spontaneous fission of 248 Cm and 252 Cf sources, using the EUROGAM-II and Gammasphere detector arrays, respectively. A high-spin isomeric state, with a half-life of 111(11) ns, is found in 93 Rb at an excitation energy of 4422.4 keV, which most likely corresponds to the fully aligned [π (g 9/2) ⊗ ν(g 7/2 h 11/2)] 27/2 − configuration. An analogous configuration is proposed for the 5297.9-keV level observed in 91 Rb. A new E3 decay branch of the 1133.9-keV isomer in 91 Rb is found, for which the rather low transition rate of B(E3) = 3.8(10) W.u. is determined. The energy of the isomeric state of 95 Rb is now proposed to be at 810.6 keV, with a spin of (9/2 +), and its half-life determined to be T 1/2 = 94(7) ns. A cascade of prompt transitions is observed on top of the 810.6-keV isomer in 95 Rb. The near-yrast structures of 91 Rb, 93 Rb, and 95 Rb are compared to the results of shell-model calculations, which support the proposed 27/2 − interpretation of states in 91 Rb and 93 Rb. An analogous 27/2 − state is expected to occur in 95 Rb, as a long-lived isomer at 3.24 MeV. No such isomeric decay could be observed in a measurement using the Lohengrin spectrometer, which shows that, if it exists, its population, following the fission of 235 U, is at least four times lower than that of the analogous 27/2 − isomer in 97 Y.

Shapes of the neutron-rich 88-94Kr nuclei

The European Physical Journal A, 2000

. 21.10.-k Properties of nuclei; nuclear energy levels -23.20.Lv Gamma transitions and level energies -25.85.Ca Spontaneous fission -27.60.+j 90 ≤ A ≤ 149

Short-lived isomers inRb94

Physical Review C, 2008

The medium-spin structure of the neutron-rich, odd-odd nucleus 94 Rb was studied by means of γ-ray spectroscopy. Excited levels were populated in the neutron-induced fission of 235 U and in the spontaneous fission of 252 Cf and 248 Cm. Two isomeric states were found at 1485.2 and 2074.8 keV with half-lives of 18 and 107 ns, respectively. The probable structures of the two isomers involve the fully aligned, proton-neutron configurations [π (g 9/2) ⊗ ν(g 7/2)] 8 + and [π (g 9/2) ⊗ ν(h 11/2)] 10 − , respectively. These new data give information on the single-particle energies in the region.

Precise atomic masses of neutron-rich Br and Rb nuclei close to the r-process path

The European Physical Journal A, 2007

The Penning trap mass spectrometer JYFLTRAP, coupled to the Ion-Guide Isotope Separator On-Line (IGISOL) facility at Jyväskylä, was employed to measure the atomic masses of neutron-rich 85−92 Br and 94−97 Rb isotopes with a typical accuracy less than 10 keV. Discrepancies with the older data are discussed. Comparison to different mass models is presented. Details of nuclear structure, shell and subshell closures are investigated by studying the two-neutron separation energy and the shell gap energy.

New neutron-rich microsecond isomers observed among fission products ofU238at 80 MeV/nucleon

Physical Review C, 2009

Eight new isomeric states in neutron-rich nuclides have been discovered in fission fragments produced by the reaction of an 80 MeV/nucleon 238 U beam with a 9 Be target and separated in-flight using the A1900 fragment separator. The experiment was conducted at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University. Gamma rays were detected in a high-purity germanium detector located at the focal plane within a time window of 20 µs following ion implantation. In some cases the isomers were observed to decay into previously reported states, allowing us to assign the initial decay from the isomeric state. Among the outcomes, the results suggest that many studies on the nuclear structure of medium-mass neutron-rich nuclei are feasible at projectile fragmentation facilities using induced fission.

Neutron-proton multiplets in the nucleusBr88

Physical Review C, 2015

Medium spin excited levels in 88 Br populated in fission of 235 U induced by neutrons have been observed for the first time. The measurement of γ radiation following fission has been performed using the EXILL array of Ge detectors at the cold-neutron beam facility PF1B of the Institut Laue-Langevin (ILL), Grenoble. The ground state of 88 Br is proposed to be 1 − , changing the adopted (2 −) value. The low-energy, newly observed levels are members of the πp 3/2 ν(d 5/2) 3 and πf −1 5/2 ν(d 5/2) 3 multiplets. A triplet of yrast levels observed at around 2 MeV is interpreted as being due to coupling of the g 9/2 proton to the (d 5/2) 3 , seniority 3 multiplet, supporting the presence of collective effects in 88 Br. The position of the g 9/2 proton intruder in the 78 Ni core is determined at 5.7 MeV above the f 5/2 proton level. Shell-model calculations predict the same proton-neutron excitations proposed in 88 Br.