Effects of the shape in a finite fermion system

The effects of the shape of a finite fermion system on its collective modes of excitations remain a subject of intense research. This experimental evidence comes from different fields of research. For example, an ultracold cloud of ~ 4 × 105 6Li atoms exhibits collective angular oscillation about a principal axis of the elliptic trap when the angle of the trap is suddenly rotated by ~ 5°. Another piece of evidence is the observation of strong dipole and quadrupole resonances in ultrasmall two-dimensional systems comprised of ~20 electrons per quantum dot, where the system can be described by an effective parabolic potential. However, the most well studied system of this class is the deformed atomic nucleus, which is a classic example of a quantum rotor. In this case, the effects of the shapes manifest in the high spin level structures of these deformed nuclei. In this presentation, I shall describe the experiments which we have carried out with the Indian National Gamma Array at the Pelletron accelerators to establish the high spin level structures of nuclei in the mass-100 region. The relation between the observed level structures and the different shapes of these nuclei will be discussed [1- 5]. [1] S. Roy et. al, Phys. Lett. B 694 , 322 (2011). [2] S. Roy et. al, Phys. Lett. B 710, 587 (2012). [3] P. Datta et. al, Phys. Rev. C. 78, 021306(R) (2008). [4] N. Rather et. al, Phys. Rev. C89, 061303 (R) (2014). [5] N. Rather et. al, Phys. Rev. Lett 112, 202503 (2014).