Single-particle structure of neutron-rich Sr isotopes via H-2(Sr-94,Sr-95,Sr-96, p) reactions

Background: The region around neutron number N = 60 in the neutron-rich Sr and Zr nuclei is one of the most dramatic examples of a ground-state shape transition from (near) spherical below N = 60 to strongly deformed shapes in the heavier isotopes. Purpose: The single-particle structure of Sr95-97 approaching the ground-state shape transition at Sr-98 has been investigated via single-neutron transfer reactions using the (d, p) reaction in inverse kinematics. These reactions selectively populate states with a large overlap of the projectile ground state coupled to a neutron in a single-particle orbital. Method: Radioactive Sr-94,Sr-95,Sr-96 nuclei with energies of 5.5 A MeV were used to bombard a CD2, where D denotes H-2, target. Recoiling light charged particles and gamma rays were detected using a quasi-4 pi silicon strip detector array and a 12-element Ge array. The excitation energy of states populated was reconstructed employing the missing mass method combined with gamma-ray tagging and differential cross sections for final states were extracted. Results: A reaction model analysis of the angular distributions allowed for firm spin assignments to be made for the low-lying 352, 556, and 681 keV excited states in Sr-95 and a constraint has been placed on the spin of the higher-lying 1666 keV state. Angular distributions have been extracted for ten states populated in the 2H(Sr-95, p)Sr-96 reaction, and constraints have been provided for the spins and parities of several final states. Additionally, the 0, 167, and 522 keV states in Sr-97 were populated through the 2H(Sr-96, p) reaction. Spectroscopic factors for all three reactions were extracted. Conclusions: Results are compared to shell-model calculations in several model spaces and the structure of low-lying states in Sr-94 and Sr-95 is well described. The spectroscopic strength of the 0(+) and 2(+) states in Sr-96 is significantly more fragmented than predicted. The spectroscopic factors for the H-2(Sr-96, p)Sr-97 reaction suggest that the two lowest-lying excited states have significant overlap with the weakly deformed ground state of Sr-96, but the ground state of Sr-97 has a different structure.