Study of collectivity in neutron-deficient A ≅ 120 nuclei close to the proton drip line

This thesis reports on spectroscopic studies of very neutron-deficient nuclei in the mass region A≅120. We performed the fusion evaporation reaction ⁶⁴Zn+⁵⁸Ni and used the Jurogam 3 + MARA setup located at JYFL, Finland. More than 15 nuclei were produced in this reaction. Our study was mainly focused on three isotopes: ¹²⁰La, ¹¹⁷Cs, and ¹¹⁴I. We identified excited states in ¹²⁰La for the first time which makes ¹²⁰La the lightest isotope of lanthanum known spectroscopically. The observed states are organized in a cascade built on the ground state and a rotational band built on the πh_11/2 x νh_11/2 configuration. Cranked Nilsson Strutinsky calculations were performed to estimate the deformation parameters, and a two-quasiparticle plus triaxial rotor model was employed to describe the signature inversion and B(M1)/B(E2) transition probabilities. In the case of ¹¹⁷Cs, we found three new bands, established the ground state, and the excitation energies of bands 1 and 2. With the help of the mass spectra obtained at the focal plane of the MARA separator and the X-rays observed in the Jurogam 3 detector, we firmly assigned all the observed bands to ¹¹⁷Cs. Particle number conserving cranked shell model calculations were performed to check the assigned configurations to all bands. The calculations suggest that ¹¹⁷Cs is a deformed nucleus with ε₂≅0.32. We also studied the level structure of ¹¹⁴I, in which we found several low-lying states characterized by a small deformation, and three rotational bands at higher excitation energy based on larger deformation. We established the band head energy of all bands and thereby identified the ground state. Three new isomers were identified based on the imbalance in the intensities. The shell-model calculations suggest a prolate-oblate shape coexistence in ¹¹⁴I. In all this work, spins and parities were assigned based on angular correlation and polarisation measurements. We also performed a detailed analysis of the rotational properties of all identified bands, which helped us to understand the physics behind the level structure. (author)