First spectroscopy of 61Ti and the transition to the Island of Inversion at N = 40

Abstract Isomeric states in 59,61 Ti have been populated in the projectile fragmentation of a 345 A MeV 238 U beam at the Radioactive Isotope Beam Factory. The decay lifetimes and delayed γ -ray transitions were measured with the EURICA array. Besides the known isomeric state in 59 Ti, two isomeric states in 61 Ti are observed for the first time. Based on the measured lifetimes, transition multipolarities as well as tentative spins and parities are assigned. Large-scale shell model calculations based on the modified LNPS interaction show that both 59 Ti and 61 Ti belong to the Island of Inversion at N = 40 with ground state configurations dominated by particle-hole excitations to the g 9 / 2 and d 5 / 2 orbits.