Precision Mass Measurements of Neutron-Rich Co Isotopes Beyond N=40

For many years, the region near Z=28, N=40 has been a subject of great interest for the nuclear structure community due to spectroscopic signatures in $^{68}$Ni suggesting a subshell closure at N=40. Mass surfaces and their derivatives provide a complementary approach to shell structure investigations via separation energies, and mass measurements can therefore play an important role in understanding shell structure in the region of $^{68}$Ni. Penning trap mass spectrometry has provided precise measurements for a number of nuclei in this region, however a complete picture of the mass surfaces has so far been limited by the large uncertainty remaining for nuclei with N$>$40 along the iron and cobalt chains. Here we shall present the first Penning trap measurements of $^{68,69}$Co, performed at the Low Energy Beam and Ion Trap facility at the National Superconducting Cyclotron Laboratory, and discuss the importance of these measurements for understanding the evolution of nuclear structure in the region of $^{68}$Ni.