Negative $g$ factor for the 4$^+_1$ state in $^{86}$Sr: a test of the shell model near $N$ = 50

Lifetimes and $g$ factors of several low-lying states have been measured by Coulomb excitation, in inverse kinematics. The $_{38}^{86}$Sr$_{48}$ nucleus lies near the $N$ = 50 shell closure. $^{86}$Sr is a particularly interesting case because $^{88}$Sr is often taken as the core nucleus in shell model calculations in this region. Noteworthy results of the experiment include the negative $g$ factor for the 4$^+_1$ state of $^{86}$Sr, in contrast to the positive $g$ factor of the 2$^+_1$ state, and similarities between the two isotones $^{86}$Sr and $^{88}$Zr. Large scale shell model calculations using the JJ4B and JUN45 interactions have been carried out. The results will be presented and compared to the data from the $^{84-102}$Zr and $^{84,88}$Sr isotopes.