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

Abstract

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 95–97Sr approaching the ground-state shape transition at 98Sr 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 94,95,96Sr nuclei with energies of 5.5 AMeV were used to bombard a CD2, where D denotes 2H, target. Recoiling light charged particles and γ rays were detected using a quasi-4π 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 γ-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 95Sr 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(95Sr,p)96Sr reaction, and constraints have been provided for the spins and parities of several final states. Additionally, the 0, 167, and 522 keV states in 97Sr were populated through the 2H(96Sr,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 94Sr and 95Sr is well described. The spectroscopic strength of the 0+ and 2+ states in 96Sr is significantly more fragmented than predicted. The spectroscopic factors for the 2H(96Sr,p)97Sr reaction suggest that the two lowest-lying excited states have significant overlap with the weakly deformed ground state of 96Sr, but the ground state of 97Sr has a different structure.