Manifestations of non-axial shapes in nuclei

 Gopal Mukherjee (Variable Energy Cyclotron Centre, India)

 The atomic nucleus is a many-body quantum system, in which the nucleons are bound by short range attractive strong force. It is interesting that such a tiny quantal system possesses different shapes and structures, which are the manifestations of the breaking of different quantum mechanical symmetries. For example, the prolate or oblate deformed shapes are the results of the breaking of spherical symmetry, often affected by some particular nucleonic orbits. The non-axial shape in a nucleus occurs when the axial symmetry is broken. It is not well understood yet what exactly causes the various symmetry breaking. The lowest order nuclear deformation is quantified by two parameters, β2 and γ. The complex dependence of the nucleonic shells on these two parameters results in minimum of nuclear potential for a particular set of values of β2 and γ, which defines the nuclear shape. In order to experimentally verify the shapes, in particular the non-axial shape of a nucleus, one has to identify its various manifestations. The primary finger print of nuclear shape is its “level scheme”. The nuclear wobbling motions [1], gamma-vibration [2] and nuclear chirality [3] are to name a few manifestations of non-axial nuclear shapes which could be identified as different types of “band structures” in the level scheme of a nucleus. In addition, the breaking of reflection symmetry gives rise to octupole correlation and octupole shapes in nuclei [4,5]. An octupole band in the level scheme is a result of an octupole shape. The set of excited states that a nucleus can have, is constructed from the high-resolution gamma-ray spectroscopy measurements. We have performed such measurements at VECC, Kolkata using light and heavy-ion beams from the K-130 cyclotron and utilizing the Indian National Gamma Array (INGA) as the gamma-ray spectrometer. In our work, we have identified different manifestations of these shapes in nuclei with proton and/or neutron numbers around the magic numbers 28, 50 or 82. Some of these results and the role of the single-particle orbitals near these magic numbers will be discussed in the presentation. 

[1] S. Nandi, GM, et al., Phys. Rev. Lett 125, 132501 (2020). 
[2] S. Nandi, GM, et al., Phys. Rev. C 105, 034336 (2022). 
[3] T. Roy, GM, et al., Physics Letters B 782 768 (2018). 
[4] S. Basu, GM, et al., Eur. Phys. J. A 59 229 (2023). 
[5] A. Karmakar, …, GM, et al., Phys. Rev. C 110, L051302 (2024).