[en] The 270-MeV ⁵⁸Ni+¹⁰²Pd 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 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 h_11/2 protons and h_9/2 neutrons plays an important role in the structure of ¹⁵⁵Yb and ^155,156Lu

[en] The last five years have witnessed a rapid increase in the volume of data on proton decaying nuclei. The path was led by decay studies with recoil mass separators equipped with double-sided Si strip detectors. The properties of many proton-decaying states were deduced, which triggered renewed theoretical interest in the process of proton decay. The decay experiments were closely followed by in-beam γ-ray studies which extended one's knowledge of high-spin states of proton emitters. The unparalleled selectivity of the Recoil-Decay Tagging method combined with the high efficiency of large arrays of Ge detectors allowed, despite small cross sections and overwhelming background from strong reaction channels, the observation of excited states in several proton emitters. Recently, in-beam studies of the deformed proton emitters ¹⁴¹Ho and ¹³¹Eu have been performed with the GAMMASPHERE array of Ge detectors and the Fragment Mass Analyzer at ATLAS. Evidence was found for rotational bands in ¹⁴¹Ho and ¹³¹Eu. The deformations and the single-particle configurations proposed for the proton emitting states from the earlier proton-decay studies were confronted with the assignments deduced based on the in-beam data. It should be noted that the cross section for populating ¹³¹Eu is only about 50 nb, and it represents the weakest channel ever studied in an in-beam experiment

[en] The majority of experiments performed during the 2-year long stay of GAMMAS-PHERE at the Argonne National Laboratory aimed to study proton-rich nuclei far from the line of stability at and beyond the proton drip-line. A high reaction channel selectivity was required to assign in-beam γ-ray transitions to weakly populated exotic nuclei in the presence of background from strong reaction channels. In many of the experiments this was achieved by using the Argonne fragment mass analyzer to separate heavy-ion fusion-evaporation reaction products from scattered beam and disperse them according to their mass-over-charge-state ratio. For medium mass and heavy a and proton emitters the Recoil-Decay Tagging method was implemented. In-beam γ-ray transitions were observed in several proton emitters between Z=50 and Z=82. Among others, rotational bands were assigned to ¹⁴¹Ho and ¹³¹Eu. A quadruple deformation of β=0.25(4) was deduced for the ground state in ¹⁴¹Ho from the extracted dynamic moment of inertia. Based on observed band crossings and signature splittings the 7/2^- [523] and 1/2⁺[411] configurations were proposed for the ground state and the isomeric state, respectively. Comparison with particle-rotor calculations indicates, however, that ¹⁴¹Ho may have significant hexadecapole deformation and could be triaxial

[en] 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. (c) 2000 The American Physical Society

[en] The γ-ray spectroscopy of even- and odd-mass isotopes of polonium have been studied using arrays of Ge detectors coupled to recoil-mass analyzers, including recoil-decay tagging techniques. The level energies and B(E2) branching ratios can be reproduced by theoretical frameworks which do not explicitly include proton particle-hole excitations across the Z=82 shell, conclusions in contrast to those deduced from alpha-decay measurements

[en] The quasicontinuous spectra associated with the decay of the superdeformed bands in ^192,194Pb have been extracted. The rapid rise in the γ-ray intensity in these spectra for E_γ(less-or-similar sign)1.8 MeV is interpreted to arise from the dramatic increase in level density above the energy gap for even-even nuclei. This energy gap has been found to be ≅0.95(10) MeV at 6(ℎ/2π) in ¹⁹⁴Pb and ≅0.4_-0.1^+0.4 MeV at 10(ℎ/2π) in ¹⁹²Pb. (c) 2000 The American Physical Society

[en] The level structures of odd A∼110 Ru, Pd, and Cd isotopes have been investigated following the fission of compound nuclei formed in heavy-ion fusion reactions. New sequences have been assigned to ¹⁰⁷Ru, and to ^{113,115,117,119}Cd isotopes using the complementary fission fragment technique. A comparison with neighboring neutron-deficient and neutron-rich odd-A Ru, Pd, and Cd isotopes supports an interpretation of these sequences as originating from the neutron h_11/2 orbital. The occupation of this orbital polarizes the nucleus to a nonaxial shape in odd-A Ru, Pd and Cd isotopes over a wide range of neutron numbers. The yrast bands in the ^{114,116,118,120}Cd cores have been extended to higher spins and excitation energies. (c) 2000 The American Physical Society