Mapping the N = 40 Island of Inversion: Precision Mass Measurements of Neutron-rich Fe Isotopes
Abstract
Nuclear properties across the chart of nuclides are key to improving and validating our understanding of the strong interaction in nuclear physics. We present high-precision mass measurements of neutron-rich Fe isotopes performed at the TITAN facility. The multiple-reflection time-of-flight mass spectrometer (MR-ToF-MS), achieving a resolving power greater than 600\,000 for the first time, enabled the measurement of 63-70Fe, including first-time high-precision direct measurements (δ m/m 10-7) of 68-70Fe, as well as the discovery of a long-lived isomeric state in 69Fe. These measurements are accompanied by both mean-field and ab initio calculations using the most recent realizations which enable theoretical assignment of the spin-parities of the 69Fe ground and isomeric states. Together with mean-field calculations of quadrupole deformation parameters for the Fe isotope chain, these results benchmark a maximum of deformation in the N = 40 island of inversion in Fe, and shed light on trends in level densities indicated in the newly-refined mass surface.
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