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The decays of the πd3/2 ground states of 156Ta and 160Re have been studied in detail using the GREAT spectrometer. More than 7000 160Re nuclei were produced in reactions of 290- and 300-MeV 58Ni ions with an isotopically enriched 106Cd target and separated in flight using the RITU separator. The proton and α decays of the πd3/2 level were confirmed and the half-life and branching ratios of this state were determined with improved precision to be t1/2=611±7 μs and bp=89±1% and bα=11±1%, respectively. The α-decay branch populated the ground state of 156Ta, allowing improved values for the proton-decay energy and half-life to be obtained (Ep=1011±5 keV; t1/2=106±4 ms). The β decay of this level was identified for the first time and a branching ratio of bβ=29±3% was deduced. The spectroscopic factors deduced from these measurements are compared with predictions.
Doppler Shift Attenuation Method (DSAM) analysis of excited-state lifetimes normally employs thin production targets mounted on a thick stopper foil (“backing”) serving to slow down and stop the recoiling nuclei of interest in a well-defined manner. Use of a thick, homogeneous production target leads to a more complex analysis as it results in a substantial decrease in the energy of the incident projectile which traverses the target with an associated change in the production cross section of the residues as a function of penetration depth. Here, a DSAM lifetime analysis using a thick homogeneous target has been verified using the Doppler broadened lineshapes of γ rays following the decay of highly excited states in the semi-magic (N = 50) nucleus 94Ru. Lifetimes of excited states in the 94Ru nucleus have been obtained using a modified version of the LINESHAPE package from the Doppler broadened lineshapes resulting from the emission of the γ rays, while the residual nuclei were slowing down in the thick (6 mg/cm2 ) metallic 58Ni target. The results have been validated by comparison with a previous measurement using a different (RDDS) technique.
Excited states in the neutron-deficient nuclides 162 74 W88 and 164 74 W90 were investigated by using the γ -ray spectrometer Jurogam. A change in structure is apparent from the first rotational alignments in 162W and 164W, whose rotationally aligned bands are interpreted as ν(h9/2) 2 and ν(i13/2) 2 configurations, respectively. The level schemes have been extended using recoil (-decay) correlations with the observation of excited collective structures. Configuration assignments have been made on the basis of comparisons of the deduced aligned angular momentum, as a function of rotational frequency, with the predictions of the cranked shell model.
Lifetimes of negative-parity states have been determined in the neutron deficient semi-magic (N = 50) nucleus 95Rh. The fusion-evaporation reaction 58Ni(40Ca,3p) was used to populate high-spin states in 95Rh at the Grand Accélérateur National d’Ions Lourds (GANIL) accelerator facility. The results were obtained using the Doppler Shift Attenuation Method (DSAM) based on the Doppler broadened line shapes produced during the slowing down process of the residual nuclei in a thick 6mg/cm2 metallic target. B(M1) and B(E2) reduced transition strengths are compared with predictions from large-scale shell-model calculations.
Excited states in the neutron-deficient nuclei 163 75 Re88 and 165 75 Re90 were populated in the 106Cd(60Ni, p2nγ ) and 92Mo(78Kr, 3p2nγ ) fusion-evaporation reactions at bombarding energies of 270 and 380 MeV, respectively. γ rays were detected at the target position using the JUROGAM spectrometer while recoiling ions were separated in-flight by the RITU gas-filled recoil separator and implanted in the GREAT spectrometer. The energy level schemes for 163Re and 165Re were identified using recoil-decay correlation techniques. At low spin, the yrast bands of these isotopes consist of signature partner bands based on a single πh11/2 quasiproton configuration. The bands display large energy splitting consistent with the soft triaxial shape typical of transitional nuclei above N = 82. The configurations of the excited states are proposed within the framework of the cranked shell model.
Lifetimes of excited states in the yrast band of the neutron-deficient nuclide 166W have been measured utilizing the DPUNS plunger device at the target position of the JUROGAM II γ -ray spectrometer in conjunction with the RITU gas-filled separator and the GREAT focal-plane spectrometer. Excited states in 166W were populated in the 92Mo(78Kr,4p) reaction at a bombarding energy of 380 MeV. The measurements reveal a low value for the ratio of reduced transitions probabilities for the lowest-lying transitions B(E2; 4+ → 2+)/B(E2; 2+ → 0+) = 0.33(5), compared with the expected ratio for an axially deformed rotor (B4/2 = 1.43).