Wobbling Motion in Nuclei: Transverse, Longitudinal and Chiral

<p>Triaxial nuclear shapes are a very rare phenomena that are manifested experimentally via their unique signatures - chiral rotation and wobbling motion. The present work was aimed at studying these exotic rotational modes in two different regions of the nuclear chart viz. A ∼ 130 and 190. </p><p>Within the A ∼ 130 region, the primary focus of the present work was to study the 135Pr nucleus. This nucleus was the first case of wobbling observed outside of the well-studied A ∼ 160 region. Aided with a high-statistics measurement using the Gammasphere array at the Argonne National Laboratory, the present work was able to observe a second phonon (nω = 2) wobbling band in this nucleus. The nature of the wobbling bands was confirmed by the characteristic predominantly E2 nature of the nω+1 → nω linking transitions based on angular distribution measurements. These results sufficiently established the presence of wobbling motion in the A ∼ 130 region, independent of any particular spin or deformation. </p><p>In addition to the nω = 1 and nω = 2 wobbling bands, two chiral-partner bands with the configuration πh11/2 × νh11/2^2 have also been observed in 135Pr. Angular distribution analyses of the ∆I = 1 connecting transitions between the two chiral partners revealed a mixed M1/E2 nature. Based on these observations, 135Pr has been proposed to be the first observed case of a chiral wobbler wherein chiral rotation has been observed in coexistence with wobbling motion.</p><p>Beyond the A ∼ 130 region, the present work has also investigated the A ∼ 190 region to seek for evidence of nuclear wobbling motion. Experiments using the Gammasphere array were performed to populate levels in the 187 Au nucleus and a detailed analysis revealed two separate wobbling bands built on (πh9/2)1 and (πh1/2)−1 configurations. Based on angular distribution measurements, the ∆I = 1, E2 nature of the nω+1 → nω transitions was verified. The two structures so-observed were found to exhibit different types of wobbling: transverse and longitudinal. 187Au has hence been observed as a case of the first cleanly established longitudinal wobbler and of the possible coexistence of both forms of wobbling, a phenomenon never observed before.</p><p>Theoretical interpretations for the above work have been done within the framework of the Particle Rotor Model, the Quasiparticle Triaxial Rotor Model and the Triaxial Projected Shell Model and a good agreement with the experimental values has been obtained.</p>