*Review* **Reaching into the** *N* **<sup>=</sup> 40 Island of Inversion with Nucleon Removal Reactions**

**Alexandra Gade 1,2**

<sup>1</sup> FRIB Laboratory, Michigan State University, East Lansing, MI 48824, USA; gade@nscl.msu.edu

<sup>2</sup> Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824, USA

**Abstract:** One ambitious goal of nuclear physics is a predictive model of all nuclei, including the ones at the fringes of the nuclear chart which may remain out of experimental reach. Certain regions of the chart are providing formidable testing grounds for nuclear models in this quest as they display rapid structural evolution from one nucleus to another or phenomena such as shape coexistence. Observables measured for such nuclei can confirm or refute our understanding of the driving forces of the evolution of nuclear structure away from stability where textbook nuclear physics has been proven to not apply anymore. This paper briefly reviews the emerging picture for the very neutron-rich Fe, Cr, and Ti isotopes within the so-called *N* = 40 island of inversion as obtained with nucleon knockout reactions. These have provided some of the most detailed nuclear spectroscopy in very neutron-rich nuclei produced at rare-isotope facilities. The results indicate that our current understanding, as encoded in large-scale shell-model calculations, appears correct with exciting predictions for the *N* = 40 island of inversion left to be proven in the experiment. A bright future emerges with predictions of continued shell evolution and shape coexistence out to neutron number *N* = 50, below 78Ni on the chart of nuclei.

**Keywords:** rare isotopes; shell evolution; *N* = 40 island of inversion; knockout reactions
