Exploring the Onset of Collectivity Approaching N=40 through Manganese Masses

Isotopes in the region of the nuclear chart below ${}^{68}\mathrm{N}\mathrm{i}$ have been the subject of intense experimental and theoretical effort due to the potential onset of a new ``island of inversion’’ when crossing the harmonic oscillator subshell closure at $N=40$. We have measured the masses of ${}^{64-68}\text{Mn}$ using TITAN’s multiple-reflection time-of-flight mass spectrometer, resulting in the first precision mass measurements of ${}^{67}\mathrm{M}\mathrm{n}$ and ${}^{68}\mathrm{M}\mathrm{n}$. These results are compared to $\mathit{\text{ab}}\mathit{\text{initio}}$ calculations and modern shell model calculations and show an increase in collectivity approaching $N=40$.