Electromagnetic transition rates in $^{70}$Ni and $^{72}$Ni

A systematic study of Ni isotopes in the vicinity of doubly-magic $^{78}$Ni will help in the understanding of shell closure effects, isomerism, and single particle states in this region of the nuclear chart. An experiment was performed at National Superconducting Cyclotron Laboratory to measure electromagnetic transition rates in $^{70}$Ni and $^{72}$Ni populated by a one-proton knockout reaction of a Cu beam. The transition rates for the $2^+ \rightarrow 0^+$ and $4^+ \rightarrow 2^+$ transitions were determined using the Recoil Distance Method, particularly suited for picosecond lifetimes, using the Segmented Germanium Array coupled with the NSCL/K\"oln plunger at the target of the S800 spectrograph. The resulting lifetimes for the low lying transitions suggest a weaker core polarization for nickel isotopes above the N=40 subshell closure than previously suggested.