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 63−70 Fe, including first-time high-precision direct measurements (δm/m ∼ 10 −7 ) of 68−70 Fe, as well as the discovery of a long-lived isomeric state in 69 Fe. 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 69 Fe 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.

Shape Coexistence in Even–Even Nuclei: A Theoretical Overview

“…Well-documented islands of inversion are known to occur [535,536] at N = 8 [537], N = 20 [533,[537][538][539][540][541][542][543], N = 28 [49,544,545], N = 40 [50,[546][547][548][549][550][551], and N = 50 [534]. Merging of the IoIs occurring at N = 20 and N = 28 has been suggested in [49,545], while merging of the IoIs occurring at N = 40 and N = 50 has been proposed in [534,551].…”

ARIEL experiments and theory

“…A program of high precision mass measurements is carried out at the TITAN (TRIUMF's Ion Trap for Atomic and Nuclear science) Penning trap facility. Research focus includes nuclear structure studies of exotic halo nuclei [3], shell evolution in neutron rich isotopes [4,5,6], precise determination of Q-values of superallowed β-decays used for the determination of the V ud matrix element of the CKM matrix [7].…”

“…Still more recently, high-precision mass measurements of neutron-rich Fe isotopes were performed at the TITAN facility using the newly commissioned multiple-reflection time-offlight mass spectrometer (MR-ToF-MS) [5]. These measurements were accompanied by inhouse ab initio VS-IMSRG calculations which enabled theoretical assignment of the spin-parities of the 69 Fe ground and isomeric states.…”