Nature of yrast excitations near N=40: Level structure of Ni-67

Excited states in Ni-67 were populated in deep-inelastic reactions of a Ni-64 beam at 430 MeV on a thick U-238 target. A level scheme built on the previously known 13 micro-s isomer has been delineated up to an excitation energy of ~5.3 MeV and a tentative spin and parity of (21/2-). Shell model calculations have been carried out using two effective interactions in the f5/2pg9/2 model space with a Ni-56 core. Satisfactory agreement between experiment and theory is achieved for the measured transition energies and branching ratios. The calculations indicate that the yrast states are associated with rather complex configurations, herewith demonstrating the relative weakness of the N=40 subshell gap and the importance of multi particle-hole excitations involving the g9/2 neutron orbital.Comment: Accepted by Physical Review

High-spin states and isomers in the one-proton-hole and three-neutron-hole 204Tl isotope

The high-spin structure of the neutron-rich 204Tl isotope has been studied up to a 11.2-MeV excitation energy and a I=30 spin range using the deep-inelastic heavy-ion γ-spectroscopy method with reactions of 48Ca on thick 208Pb and 238U targets. The established structure of yrast levels involves four isomeric states up to Iπ=22-, the highest spin state available for the maximally aligned four valence holes. The observations are interpreted and quantitatively confirmed by shell-model calculations. The rates of the identified M2 and E3 isomeric decays are discussed and a striking analogy is found for the yrast level structures and γ decays observed in the 18+ to 22- and 45/2- to 53/2+ spin ranges in 204Tl and 203Hg, respectively. In the highest spin part of the scheme, two prominently populated yrast states are tentatively identified as the 3 - 208Pb core excitation built on the 22- and 20 + maximally aligned four-hole states. Their energies are reproduced well by using energy shifts observed in experiments for the 208Pb core octupole excitation coupled to simpler intrinsic structures

Experimental study of neutron-rich nuclei 89Rb and 91Rb

Neutron-rich 89,91Rb nuclei populated as fission products in heavy-ion reactions have been studied with the Gammasphere array. The previously known level schemes have been extended to higher excitation energies and spins. Spin and parity assignments were based on angular correlation analyses. A value of T1/2 = 8(2) ns was extracted for the isomeric g9/2 state in 89Rb

Yrast structure of 97Zr

The yrast structure of the neutron-rich nucleus 97Zr has been studied using fission of target-like products in the reaction of a 48Ca beam on a thick 238U target. The level scheme known from the previous studies up to an energy and spin of approx. 4619 keV and 23/2-, respectively, has been extended by about 3 MeV and a few units of angular momentum. The located structure can be discussed in terms of shell model configurations

Yrast structure of the two-proton- and three-neutron-hole nucleus Hg203 from the decay of a 53/2+ isomer

The decay of a new, 53/2+, isomer at 8281 keV in Hg203 has been studied by γ coincidence spectroscopy. A half-life of 146(30) ns was measured. In addition, another isomeric, 39/2+, level with a half-life of 7.8(1.5) ns was observed. Some elements of the Rydstroem shell-model interaction have been adjusted to reproduce level energies in nuclei with two to four holes in the Pb208 core. With this interaction, the new states in the five-hole nucleus Hg203 are reproduced with an rms error of 105 keV

Yrast structure of Zr97 and β decay of the 27/2- high-spin isomer in Y97

The yrast structure of the neutron-rich nucleus Zr97 has been studied using fission of targetlike products in the reaction of a Ca48 beam on a thick U238 target. The level scheme, known from previous studies up to an excitation energy and spin-parity of approximately 4619 keV and 23/2-, has been extended by about 3 MeV and a few units of angular momentum. Two states fed in the β decay of the 27/2- high-spin isomer in Y97 were identified at 5570 and 5606 keV. The located level structure can be discussed in terms of shell-model configurations

Yrast structure of Fe64

The level structure of the N=38 isotone Fe64 was studied with the Ni64 + U238 reaction at 430 MeV. Several new levels were identified and compared to shell model calculations. Results show no evidence for deformation in the ground state, but a possible contribution from intruder orbitals at higher energy and spin

E2 transition probabilities for decays of isomers observed in neutron-rich odd Sn isotopes

High-spin states were investigated with gamma coincidence techniques in neutron-rich Sn isotopes produced in fission processes following 48Ca + 208Pb, 48Ca + 238U, and 64Ni + 238U reactions. By exploiting delayedand cross-coincidence techniques, level schemes have been delineated in odd 119-125Sn isotopes. Particular attention was paid to the occurrence of 19/2+ and 23/2+ isomeric states for which the available information has now been significantly extended. Reduced transition probabilities, B(E2), extracted from the measured half-lives and the established details of the isomeric decays exhibit a striking regularity. This behavior was compared with the previously observed regularity of the B(E2) amplitudes for the seniority ν = 2 and 3, 10+ and 27/2- isomers in even- and odd-Sn isotopes, respectively

Shell-model states with seniority ν=3, 5, and 7 in odd- A neutron-rich Sn isotopes

Excited states with seniority ν=3, 5, and 7 have been investigated in odd neutron-rich Sn119,121,123,125 isotopes produced by fusion-fission of 6.9-MeV/ACa48 beams with Pb208 and U238 targets and by fission of a U238 target bombarded with 6.7-MeV/ANi64 beams. Level schemes have been established up to high spin and excitation energies in excess of 6 MeV, based on multifold gamma-ray coincidence relationships measured with the Gammasphere array. In the analysis, the presence of isomers was exploited to identify gamma rays and propose transition placements using prompt and delayed coincidence techniques. Gamma decays of the known 27/2- isomers were expanded by identifying new deexcitation paths feeding 23/2+ long-lived states and 21/2+ levels. Competing branches in the decay of 23/2- states toward two 19/2- levels were delineated as well. In Sn119, a new 23/2+ isomer was identified, while a similar 23/2+ long-lived state, proposed earlier in Sn121, has now been confirmed. In both cases, isomeric half-lives were determined with good precision. In the range of ν=3 excitations, the observed transitions linking the various states enabled one to propose with confidence spin-parity assignments for all the observed states. Above the 27/2- isomers, an elaborate structure of negative-parity levels was established reaching the (39/2-), ν=7 states, with tentative spin-parity assignments based on the observed deexcitation paths as well as on general yrast population arguments. In all the isotopes under investigation, strongly populated sequences of positive-parity (35/2+), (31/2+), and (27/2+) states were established, feeding the 23/2+ isomers via cascades of three transitions. In the Sn121,123 isotopes, these sequences also enabled the delineation of higher-lying levels, up to (43/2+) states. In Sn123, a short half-life was determined for the (35/2+) state. Shell-model calculations were carried out for all the odd Sn isotopes, from Sn129 down to Sn119, and the results were found to reproduce the experimental level energies rather well. Nevertheless, some systematic deviations between calculated and experimental energies, especially for positive-parity states, point to the need to improve some of the two-body interactions used in calculations. The computed wave-function amplitudes provide for a fairly transparent interpretation of the observed level structures. The systematics of level energies over the broad A = 117-129 range of Sn isotopes displays a smooth decrease with mass A, and the observed regularity confirms most of the proposed spin-parity assignments. The systematics of the B(E2) reduced transition probabilities extracted for the 23/2+ and 19/2+ isomers is discussed with an emphasis on the close similarity of the observed A dependence with that of the E2 transition rates established for other ν=2, 3, and 4 isomers in the Sn isotopic chain

Nature of yrast excitations near N=40: Level structure of 67 Ni

Excited states in 67Ni were populated in deep-inelastic reactions of a 64Ni beam at 430 MeV on a thick 238U target. A level scheme built on the previously known 13-μs isomer has been delineated up to an excitation energy of 5.3 MeV and a tentative spin and parity of (21/2-). Shell model calculations have been carried out using two effective interactions in the f5/2pg9/2 model space with a 56Ni core. Satisfactory agreement between experiment and theory is achieved for the measured transition energies and branching ratios. The calculations indicate that the yrast states are associated with rather complex configurations, herewith demonstrating the relative weakness of the N=40 subshell gap and the importance of multi-particle-hole excitations involving the g9/2 neutron orbital