Nuclear Structure 2026

Re-emergence of identical bands phenomenon at normal deformation

Jul 28, 2026, 6:11 p.m.

1m

Fletcher Challenge Canada (Simon Fraser University Harbour Centre)

Posters Poster Session

Speaker

Pramod Kumar Nayak (Bhabha Atomic Research Centre, Mumbai 400085, India & Homi Bhabha National Institute, Anushaktinagar, Mumbai 400094, India)

Description

The rare-earth nuclei around N ~ 90 and A ~ 160 continue to present fascinating as well as challenging physics issues spanning a wide range of angular momenta. Among the many exotic phenomena characterizing nuclei in this mass region, the identical band (IB) phenomenon became a topic of intense research and discussion in the nineties. It was first identified in excited superdeformed (SD) bands of $^{150}$Gd and $^{151}$Tb [1]. Thereafter, many low-spin IBs were also reported both at intermediate (ID) and normal deformation (ND) [2]. However, further exploration of this surprising phenomenon was hindered by the lack of a global explanation valid across the entire periodic chart for all values of deformation.

The subject of “identical high-$K$ bands” at normal deformation in isotopes of a particular isotopic chain has never been investigated through dedicated measurements or theory. Following a recent measurement using a alpha beam and a moderate-size array of eleven Compton-suppressed clover HPGe detectors plus one LEPS (INGA) at the Variable Energy Cyclotron Centre (VECC), Kolkata, India, a new high-$K$ band structure was identified in the $^{162}$Er nucleus (the first-ever) above its $K^\pi=7^-$ isomer [3]. The remarkable similarity between this two-quasiproton structure and the corresponding excitation in $^{164}$Er up to the highest observed spin is intriguing [3]. Further, this finding, when discussed in combination with the two-quasiproton $K^\pi=6^+$ identical high-$K$ bands in $^{174}$Hf and $^{178}$Hf (first recognized in the present work using data from the literature), extends the observation of this phenomenon at ND in pairs of even-even nuclei in the Er and Hf isotopic chains. However, when comparing the properties of the IBs in these two isotopic pairs, it must be concluded that proposed earlier explanations in terms of a delicate cancellation between changes in deformation and pairing do not hold for the Er isotopes [3].

Hence, the present observations call for further experimental and theoretical work. On the one hand, it is important to rule out that the identicality in the present instances is accidental by searching for additional cases, while, on the other, pursue further efforts to develop a single theoretical framework able to account for the occurrence of IBs at all deformations (ND, ID and SD) across the nuclear chart.

The INGA collaboration is gratefully acknowledged. A. C. and S. M. acknowledge the financial assistance received from DAE-BRNS, Govt. of India (Project Sanction No. 37(3)/14/17/2016-BRNS). This work was supported in part by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, under Grant DE-FG02-97ER41041 (UNC), and DEFG02-97ER41033 (TUNL).

[1] T. Byrski et al., Phys. Rev. Lett. 64, 1650 (1990).
[2] C. Baktash, B. Haas, and W. Nazarewicz, Annu. Rev. Nucl. Part. Sci. 45, 485 (1995).
[3] P. K. Nayak et al., under review in Phys. Rev. C.