Onset of collectivity in^96,98Sr studied via Coulomb excitation

Abstract

Abstract.A rapid onset of quadrupole deformation is known to occur around the neutron number 60 in the neutron-rich Zr and Sr isotopes. This shape change has made the neutron-rich A = 100 region an active area of experimental and theoretical studies for many decades now. We report in this contribution new experimental results in the neutron rich 96,98 Sr investigated by safe Coulomb excitation of radioactive beams at the REX-ISOLDE facility, CERN. Reduced transition probabilities and spectroscopic quadrupole moments have been extracted from the differential Coulomb excitation cross section supporting the scenario of shape coexistence/change at N=60. Future perspectives are presented including the recent experimental campaign performed at ILL-Grenoble.

Coulomb excitation studies of shape coexistence in atomic nuclei

“…From the differential Coulomb excitation cross section it was possible to obtain the spectroscopic quadrupole moment for the 2 1 + state. The result indicates a very small deformation [13,89]. In the case of the much more collective 98 Sr the ground-state band was populated up to the 8 1 + state in addition to the 0 2 + and 2 2 + states.…”

“…Scattering of heavy ions, on the other hand, leads to multi-step excitation, and in collective nuclei a large number of states can be populated up to relatively high spin. Spins up to 30 ÿ have been reached in experiments with heavy projectiles on actinide targets [10,11], while in experiments using weak radioactive beams spins up to ∼10 ÿ are conceivable [12,13].…”

“…The details of the shape transition and shape coexistence in the Sr isotopes were investigated in low-energy Coulomb excitation experiments with 96 Sr and 98 Sr beams at ISOLDE [13,89]. The 96 Sr beam was produced by injecting CF 4 gas into the target ion source [69,71] and to large-scale shell model calculations [72].…”

Lifetime Measurments of Excited States in Neutron-rich Fission Fragments

“…Coulomb excitation of 96,98 Sr has yielded spectroscopic quadrupole moments and reduced transition probabilities for various low-lying states. The results have given direct evidence for the crossing of the near-spherical and well-deformed configuration between 96 Sr and 98 Sr [5]. A similar Coulomb excitation experiment for the 97,99 Rb isotopes indicates that the sudden shape transition is also present in the Rb chain and that the deformation for Rb nuclei above N = 60 is similar to the other strongly deformed nuclei in the region [6].…”

“…The results support the assigned proton configuration for the ground state and provide a measurement of the deformation of the 98 Sr core. The lifetime measurement for 99 Y is, therefore, complementary to a recent Coulomb excitation experiment which investigated the shape and shape coexistence of the low-lying states in 98 Sr using a radioactive beam from the ISOLDE facility at CERN [5].…”