We report on the measurement of the first 2 + and 4 + states of 66 Cr and 70,72 Fe via in-beam γ-ray spectroscopy. The nuclei of interest were produced by (p, 2p) reactions at incident energies of 260 MeV/nucleon. The experiment was performed at the Radioactive Isotope Beam Factory, RIKEN using the DALI2 γ-ray detector array and the novel MINOS device, a thick liquid hydrogen target combined with a vertex tracker. A low-energy plateau of 2 + 1 and 4 + 1 energies as a function of neutron number was observed for N≥38 and N≥40 for even-even Cr and Fe isotopes, respectively. State-of-the-art shell model calculations with a modified LNPS interaction in the pf g 9/2 d 5/2 valence space reproduce the observations. Interpretation within the shell model shows an extension of the Island of Inversion at N=40 for more neutron-rich isotopes towards N=50. Atomic nuclei are the place of a complex interplay between single-particle configurations and correlations which strongly determine their quantum coherent wavefunctions. All over the nuclear chart, the so-called magic numbers of nucleons define boundaries of large areas of deformation. This picture, mainly established for stable nuclei and neighbors, is re-examined at the light of new available nuclei with an unbalanced proton-to-neutron ratio, with the underlying question of the persistence or evolution of magic numbers [1,2]. Specific terms of the nuclear interaction can induce the formation of shell gaps or the lowering of relative orbital energies which, combined with correlations, sometimes lead to energetically favored intruder states as the ground state configuration [3][4][5][6][7][8]. Regions where two-particle two-hole (2p2h) configurations are favored over normally-filled orbitals by quadrupole correlations have been termed as Islands of Inversion (IoI) [9][10][11]. The N=20 IoI in the vicinity of 32 Mg has provided unique information on shell evolution [12]. This IoI does not show any decrease in collectivity for Mg isotopes at N > 24 and merges with the N=28 deformation region [8,13]

Gaudefroy et al. Reply: Reference [1] aimed, in particular, at determining the variation of the neutron p 3=2 ÿ p 1=2 spin-orbit splitting (SO) between 49 20 Ca and 47 18 Ar due to the removal of 2 protons. This was achieved by using the experimental energy difference between the 3=2 ÿ 1 and 1=2 ÿ 1 states in the two nuclei. However, as soon as one departs from a doubly magic nucleus the single-particle strength of the p 3=2 and p 1=2 states becomes fragmented as they couple to excitations of the core nucleus. Therefore, Signoracci and Brown [2] pointed out that the prescription of Baranger [3] should be used to determine the singleparticle centroid energy by including both the particle and hole strengths for the p 3=2 and p 1=2 states. In practice, the full strength is rarely obtained experimentally and the observed states carry a various fraction of it. In 49 Ca 29 , 85(12)% and 91(15)% of the single-particle strengths of the p 3=2 and p 1=2 states are contained in the first 3=2 ÿ and 1=2 ÿ states, respectively. In 47 Ar 29 , these strengths are reduced to 61(5)% and 81(6)%, respectively. Therefore the determination of SO requires an adjustment of the proton-neutron monopole matrix elements V pn involving the p orbits to reproduce experimental data, after having included the proper nuclear correlations.Shell model calculations using the sdfp interaction by Nummela et al.[4] exhibit deviations of binding energies of up to 400 keV for the 3=2 ÿ and 1=2 ÿ states in the 45;46;47 Ar and 47;48;49 Ca nuclei. Therefore, contrary to Ref.[2], we have modified the relevant neutron-proton monopole interactions V pn to reproduce the experimental binding energies and spectroscopic factors of the known p states in 45;47 Ar [1,5] and 47;49 Ca [6]. By this means, the particle strengths of the p 3=2 and p 1=2 orbits, P C 2 S (using the notation of [2]), agree with the results of the 46 Ard; p 47 Ar reaction [1]. Similarly the hole strength of the p 3=2 orbital, P C 2 S ÿ , is in accordance with the result of the 1-neutron knock-out reaction 46 Arÿ1 n 45 Ar [7]. These features show that the shell model account well for the splitting of the single-particle strength due to correlations. Proton correlations are essentially due to the quasidegeneracy between the s 1=2 and d 3=2 orbits. The vacancy numbers [2j 1 ÿ occupation number] of the proton s 1=2 , d 3=2 , and d 5=2 orbits in the ground state of 46 Ar are 0.83, 1.05 and 0.12, respectively. In 48 Ca all sd orbits are fully occupied and vacancy values are null. The resulting ground-state wave function (WF) of 46 Ar contain equal mixing of s 1=2 2 d 3=2 2 and s 1=2 0 d 3=2 4 configurations. Neutron correlations are due to particle hole (p ÿ h) excitations across the N 28 shell gap. About 50% of the ground-state WF of 46 Ar correspond to 0p ÿ 0h (or f 8 7=2 ) neutron closed-shell configuration. The 1p ÿ 1h and 2p ÿ 2h excitations correspond each to 20% of the WF. Higher order excitations provide the remaining strength.The 3=2 ÿ 1 state observed in 47 Ar exhibits about 55% of 1p ÿ ...