L. L. Riedinger

Shape coexistence and alignment processes in the light Pt and Au region

Abstract High-spin states were populated in 185 Au via the 170 Yb( 19 F, 4n) 185 Au reaction. The shape coexistence of both prolate and oblate band structures was observed. In the prolate bands the two-quasiparticle πh 9 2 and νi 13 2 alignment processes are seen to occur at similar frequencies. The upbend observed in 184 Pt is then interpreted as resulting from a double crossing involving both of these processes. Strong evidence is presented for the first identification of a low-lying f 7 2 structure in nuclei below lead.

Rotation-aligned coupling and axial asymmetry in 189−195Au

Abstract Levels in 189, 191, 193Au have been studied by radioactive decay of isotopically separated 189, 191, 193Hg. The systematics of the levels are followed from 195Au to 189Au and show a remarkable insensitivity to neutron number. The h 1 1 2 bands are identified and provide a critical test of the model of a single-j nucleon subject to rotation-aligned coupling to an asymmetric core. Within the framework of the model the triaxial degree of freedom appears to be very stable.

The cranking model applied to Yb bands and band crossings

Abstract In-beam γ-ray spectroscopy experiments have been performed on 160, 161, 162 Yb in Copenhagen and on 160 Yb in Oak Ridge. Fifteen rotational sequences (bands) were observed, most of them beyond I = 20. Thirteen band crossings (upbends or backbends) were found, and these are classified according to the frequency and the gain in aligned angular momentum in the crossing. Six negative-parity side bands in 160,162 Yb and the i 13 2 band in 161 Yb experience a similar crossing around ω = 0.36 MeV/ h , a value intermediate to the frequencies of the first and second yrast backbends in 160 Yb. Cranking model calculations are used to suggest quasiparticle assignments for the bands and to explain the nature of the three basic types of band crossings observed in our measurements.

Signature inversion in semi-decoupled bands: residual interaction between protons and neutrons ☆

Abstract Semi-decoupled bands based on the πh 9 2 ⊗ vi 13 2 configuration are observed in 162 Tm, 164 Tm and 174 Ta. Spins assigned to these bands imply an inversion of the expected signature splitting, which is interpreted as being the result of a residual proton-neutron interaction.

Alignment processes and shape variations in 184Pt

Abstract High-spin states in the transitional nucleus 184Pt were populated via the reactions 154Sm(34S, 4n)184Pt and 172Yb(16O, 4n)184Pt. The yrast band was extended up to I = 28 ħ and six new side bands built on both neutron and proton quasiparticle configurations were observed. Shell correction-type calculations indicate variations of the nuclear shape in different bands, especially as a result of band crossings due to the process of angular momentum alignment. Comparison of the band characteristics are made between 184Pt and eight adjacent nuclei. The pattern of band crossings in these nine nuclei is considered from the viewpoint of blocking comparisons and of theoretical calculations. The competition between low-frequency vi 13 2 and πh 9 2 band crossings is discussed.

The Limits of Studying High-Spin States by Discrete-Line Gamma-Ray Spectroscopy

Recent (HI, xn) data on rotational Yb and Hf nuclei are used to describe the motivations and techniques for pushing discrete-line spectroscopy to the realm of the weakly populated yrast and non-yrast states. Three aspects of these studies are discussed: extraction of moments of inertia in different aligned bands, observation and understanding of high-frequency band crossings, and dependence of feeding patterns on nuclear structure.

Prediction of hyperdeformed nuclear states at very high spins

Abstract Calculations based on the generalized cranking-Strutinsky method with the deformed Woods-Saxon potential predict the existence of extremely elongated hyperdeformed nuclear shapes with the axis ratios significantly exceeding 2:1. The strongest effect is expected to take place for nuclei around 166 Er, 168 Yb, and 170 Hf ( Z = 68, 70, 72; N = 98) for spins as high as the fission limit down to I ∼ 10–20. The chances for observing those states in nature are discussed in detail. Systematic occurrences of the superdeformed and hyperdeformed states also in lighter ( A ∼ 70, and A ∼ 100) nuclei are suggested as a consequence of the approximate pseudo-oscillator (or pseudo-SU(3) symmetries of the realistic nuclear mean field.

Identification of excited structures in proton unbound nuclei 173,175,177Au: shape co-existence and intruder bands

Abstract Excited states in the proton-unbound 173,175,177 Au nuclei were identified for the first time. Level structures associated with three different shapes were observed in 175 Au. While the yrast lines of 175 Au and 177 Au consist of a prolate band built upon the intruder 1/2 + [660] ( i 13/2 ) proton orbital, no sign of collectivity was observed in the lighter 173 Au isotope. Implications for the deformation associated with these structures are discussed with a focus on shape co-existence in the vicinity of the proton-drip line.

High-spin states in 183Pt

Abstract High-spin states in 183 Pt have been studied for the first time using the reactions 154 Sm( 34 S, 5n) and 170 Yb( 16 O,3n). Rotational bands built on the Nilsson configurations 1 2 − [521], 7 2 − [514] and 9 2 + [624] were observed up to spin values of 39 2 − 49 2 h . Quasiparticle alignments and band crossing frequencies were investigated in these bands. A large signature splitting was observed in the νi 13 2 - band structure . The experimental results were compared with total routhian surface calculations, in which the shape of the nucleus could be followed as a function of rotational frequency for different quasiparticle configurations.

Experimental estimates of quasiparticle interactions for rotational nuclei

Abstract Previously presented data on rotationally aligned quasiparticle bands in 160,161,162,163 Yb are analyzed to give experimental values of the quasiparticle interactions V μν as a function of rotational frequency. The measured level energies are converted to the rotating frame of reference and expressed as routhians. The routhian of a multi-quasiparticle band is compared to the sum of the routhians of the component quasiparticles at a given frequency, the difference being the quasiparticle interaction. The experimental spectra of bands in these nuclei are consistent with the assumption of a binary interaction between the rotating quasiparticles, where most of the V μν are in the range −0.3 to −0.1 MeV. Analysis of the shift in the observed crossing frequencies for bands of different quasiparticle number yields similar values. The extracted V μν are found to have a frequency dependence, which is associated with the loss of alignment of a multi-quasiparticle state. An equidistant-level model is used to estimate the contributions to the quasiparticle interactions by polarization of the collective degrees of freedom. This model yields typical V μν values of −0.15 MeV, which is only half of some values extracted from experiment. This suggests that the extracted V μν contain a significant amount of nuclear-structure information.