Transition from collectivity to single-particle degrees of freedom from magnetic moment measurements on 3882 Sr 44 and 3890 Sr 52

Background: The 3888Sr and 4090Zr nuclei have been utilized as closed cores for large-scale shell-model calculations in the 28≤Z≤50 region around the N=50 shell. Measurements of magnetic moments for nuclei in this region would provide microscopic information about the use of 88Sr and 90Zr as stable closed-core nuclei. While the g factors of the 21+ states in the stable Sr isotopes have been previously measured, experimental g factors for the radioactive 82,90Sr have not been obtained to date. Purpose: The purpose was to measure the g factors of the 21+ and 41+ states in the unstable 82Sr and 90Sr nuclei in order to extend the systematics along the Sr isotopic chain. A comparison of the structure of the N=52 isotopes 90Sr and 92Zr will shed light on the relative robustness of proton subshell closures at Z=38 and Z=40. Methods: The pickup reaction of α particles in inverse kinematics together with the transient field technique were applied to beams of 78Kr and 86Kr at the Cyclotron Institute of Texas A&M University. Results: The values g(82Sr;21+)=+0.44(19), g(82Sr;41+)=+0.53(39), g(90Sr;21+)=-0.12(11), and g(90Sr;41+)=-0.02(17) were measured for the first time. Simultaneously, the g factors of the low-lying states in the Coulomb-excited beam projectiles were remeasured. The g(41+) = +1.03(14) in 86Kr was also measured for the first time. Conclusions: For 82Sr both g factors are in agreement with the collective value Z/A expected for nuclei in the middle of a major shell. The g factors in 90Sr are negative but smaller than in the isotone 92Zr. The results also indicate that 88Sr is a proton-soft core nucleus and perhaps even softer than 90Zr.