Second Irregularity in the Yrast Line ofYb160

γ−γ energy correlations in 167,168Hf observed with two compton-suppression spectrometers

“…This indicates that the higher bandcrossing phenomena involve most likely the i13/2 and f7/2 neutron and the h11/2 proton orbitals. It may be noticed that the presently found irregularity at hCOc3 = 0.42 MeV corresponds almost exactly with that of the observed second backbending in 158Er [1] and 160yb [2], which was ascribed as being due to the hll/2 proton orbital. The highest observed irregularity at//COc4 = 0.52 MeV is close to the one observed at ~0.55 MeV in a similar work [6], but employing single detectors.…”

“…Several groups have started searches for possible second and higher bandcrossing phenomena. Although the second backbending has been established by now [ 1,2] it occurs at such a high rotational frequency that the signifying transitions are very difficult to observe as discrete peaks in the 3,-ray spectrum. Recently a new method has been proposed [3] to isolate energy 1 Present address: Argonne National Laboratory, Argonne, IL 60439, USA.…”

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

“…A second yrast crossing has been observed in isSEr [10], 160 Yb [6,11], and ^Er [12], while transitions of high enough rotational frequency have been seen in 156 Dy [13] to demonstrate the absence of a similar crossing. Here we present nev results on higher spins in 1G0 Yb and on the previously unknown yrast line in i6If Hf from work at Oak Sidge, results which pertain to the second backbend.…”

Backbending in 167Hf and 168Hf and the band-crossing picture

“…There is no evidence for a possible second backbending in the yrast band of 168Hf up to spin 28, i.e. for a second band crossing up to h60 = 440 keV, as it has been observed in the lighter nuclei 156,158Er and 160yb [1][2][3][4]. On the contrary, the data suggest that if such a phenomenon occurs, it must happen at higher frequencies.…”

“…Significant progress, both experimental and theoretical, has recently been achieved in the understanding of nuclear behaviour at high-spin. For example, multiple band structure has been observed in the well-deformed nucleus 160yb up to at least/= 32 [1], and intriguing new phenomena like the existence of a second backbending around 1 = 28 have been reported for the nuclei 158Er [2], 160yb [1,3] and 156Er [4] ; these works have included the observation of discrete "y-rays. From the theoretical side, cranking-model calculations [5] allow the interpretation of the irregularities observed in the level sequences in terms of crossings between bands with different degrees of rotation-alignment; in particular, the dominant role of the i13/2 neutron orbit for the interpretation of the first backbending in all the even-even nuclei of the rare-earths region has been emphasized.…”