Shape Evolution in Exotic Nuclei Studied via Lifetime Measurements with GRETINA
In the past decades, low-lying states of atomic nuclei have been characterized based on phonon excitations or rotational motions with respect to the ground-state shape as a single basis. However, this picture could be altered significantly if different nuclear shapes are manifested in a single nucleus under extreme conditions of proton-neutron asymmetry and nuclear binding energies. In this talk, recent results obtained for the neutron-deficient 72Kr and neutron-rich 17C isotopes from excited-state lifetime measurements will be presented. In these nuclei, different intrinsic nuclear shapes coexist, resulting in the competition between prolate and oblate shapes in 72Kr at N=Z and the interplay between halo and deformed structure in 17C near the drip line.
The experiment was performed at NSCL using a combination of state-of-the-art instruments including the next-generation gamma-ray tracking array GRETINA. A novel application of the recoil distance method based on the use of multi-layer foils was demonstrated by taking advantage of excellent position and energy resolution obtainable from GRETINA. The present approach significantly extends the sensitive range of lifetimes that can be covered with a single setup and thus enables us to study several states simultaneously. Rapid shape evolution observed for 72Kr and 17C as well as the performance of GRETINA in lifetime measurements with fast rare isotope beams will be discussed.