Excited states in 155Yb and 155,156,157 Lu from recoil-decay tagging

The 270-MeV 58Ni+ 102Pd reaction was used for the first recoil-decay tagging measurement with Gamma-sphere coupled to the Fragment Mass Analyzer at Argonne National Laboratory. Level structures of 155Yb, 156Lu, and 157Lu, as well as the excited states associated with the 25/2- isomer in 155Lu, are identified for the first time. The systematical behavior of the energy levels is compared with that of neighboring isotones and isotopes. The attractive interaction between h11/2 protons and h9/2 neutrons plays an important role in the structure of 155Yb and 155,156Lu

High-K isomers in neutron-rich hafnium nuclei at and beyond the stability line

Pulsed 238U and 208Pb beams have been used to populate multi-quasiparticle high-K isomers in neutron-rich hafnium isotopes at and beyond the line of b-stability, via inelastic excitation and transfer. Spectroscopic properties and configuration assignments of several new high-K isomers are compared with earlier theoretical predictions. A striking example of the robustness of the K quantum number is demonstrated by the observed competition between E1 and E3 decay modes in 180Hf, the heaviest stable isotope of the element

Energy levels in 25198Cf populated in the α decay of 255100Fm

Gamma-ray spectra of a 20-h 255Fm source containing ∼1 mCi activity were measured with a 25% Ge detector and a low-energy photon spectrometer (LEPS). Gamma lines with intensities as low as 1.0 × 10-6% per 255Fm α decay were observed. Gamma-gamma coincidence spectra of a 255Fm sample were measured with the GAMMASPHERE array. A comparison of the γ-ray spectrum gated by the Cf Kα x-ray peak with the γ-singles spectrum provided spins of the excited states in 251Cf. The γ-ray data, in conjunction with previously measured 250Cf(d,p) reaction data, allowed us to characterize several single-particle and vibrational states above the N=152 subshell gap

High-spin excitations in 158,159,160Hf from recoil-decay tagging

The 270-MeV 58Ni+ APd reaction was used for the first recoil-decay tagging measurement with Gammasphere coupled to the Fragment Mass Analyzer at Argonne National Laboratory. Level structures of 158Hf and 159Hf are identified for the first time, and that of 160Hf is extended. The systematical behavior of the energy levels in neighboring isotones and isotopes, as well as the aligned angular momenta as a function of rotational frequency, are examined

Deformed negative-parity excitations in 71 As

High-spin states in the neutron-deficient 71As nucleus have been studied using in-beam g -ray spectroscopic techniques combined with mass identification. A new decay sequence of negative parity has been assigned to 71As and previously known sequences have been extended to higher spin and excitation. The new sequence has been identified as originating from the proton f 7/2 extruder orbital, which approaches the Fermi surface at large prolate deformations. Comparisons of experimental B(M1)/B(E2) ratios to theoretical expectations support this interpretation

Odd-even staggering in the πg9/2vg9/2 band in 72Br

High-spin positive-parity states in 72Br have been studied using the 16O+58Ni reaction. The πg9/2vg9/2 decoupled band in 72Br has been observed up to ∼10 MeV excitation energy and the expected odd-even staggering has been delineated. A larger signature splitting is observed for this band in 72Br than in the same collective structures in the heavier 74,76,78Br. No signature inversion at low spin is observed for this band in 72Br, in contrast to the heavier isotopes, 74,76,78Br, in which signature inversion is observed below ∼10(Latin small letter h with stroke sign). The observations are in general agreement with theoretical models in this mass region which predict no signature inversion for nuclei with less than 39 protons and neutrons

In-beam γ-ray spectroscopy of Pt isotopes located at the proton drip line

In-beam g rays have been observed in the neutron-deficient isotopes 170,171,172Pt using the recoil-decay tagging technique. The yrast transition sequence proposed for 172Pt indicates that the 01 bandhead of the deformed intruder band is situated about 900 keV above the weakly deformed ground state, i.e., its excitation energy has risen by about 300 keV compared to 174Pt. The measured energy of the 21 !01 transition in 170Pt supports an even larger increase in the excitation energy of the intruder configuration with the departure from the middle of the 82–126 major neutron shell. Furthermore, a band with transition energies almost identical to those found in 172Pt has been assigned to 171Pt and was interpreted as corresponding to a rotationally aligned i13/2 neutron orbital coupled to the core excitations

Multiparticle configurations in N=84 isotones located at the proton drip line

Excited states in the proton-rich N=84 isotones 72156Hf84,73157Ta84, and 74158W84 were observed using Pd102(Ni58,xp2n) reactions at 270 MeV. γ rays were detected with the Gammasphere array of Compton-suppressed Ge detectors coupled with the Argonne fragment mass analyzer and were assigned to individual reaction channels using the recoil-decay tagging method. Prompt γ-ray cascades were associated with the α decay of both the ground state and the 8+ isomeric state in Hf156, the h11/2 state in Ta157, and the 8+ isomeric state in W158. The level schemes constructed for Hf156,Ta157, and W158 are compared with these of lighter N=84 isotones and are discussed within the framework of the shell model