New isomeric transition in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi>Mg</mml:mi><mml:mprescripts/><mml:none/><mml:mn>36</mml:mn></mml:mmultiscripts></mml:math

Here, we observed a new isomeric γ transition at 168 keV in ³⁶Mg, with a half-life of T1/2=90⁢($^{+410}_{-50}$) ns. We propose that the observed transition deexcites a new 0⁺ isomeric state at 833 keV and populates the previously known first 2⁺ state. The existence of this isomer is consistent with the predictions of the large-scale shell-model calculations of ³⁶Mg using the sdpf-u-mix interaction. The observed excitation energy of the second 0⁺ state is caused by the small energy separation between two prolate-deformed configurations where the intruder configuration corresponds to two-neutron excitations from the sd to the pf shell. Within this interpretation, ³⁶Mg becomes the crossing point between nuclei in which ground state deformed/superdeformed configurations are caused by the dominance of N=20 intruders (^32,34Mg) and nuclei where deformed configurations are associated with the breaking of the N=28 closure and a large occupancy of the 1⁢p_3/2 neutron orbit (³⁸Mg and beyond). We found the lack of three-body monopole corrections in other effective interactions results in a predominance of N=20 intruder configurations past ³⁸Mg incompatible with our observation. We conclude that ³⁶Mg bridges the N=20 and N=28 islands of inversion, forming the so-called big island of deformation.. Authors: Madurga, M. [Univ. of Tennessee, Knoxville, TN (United States)] (ORCID:0000000281774328); Christie, J. M. [Univ. of Tennessee, Knoxville, TN (United States)]; Xu, Z. [Univ. of Tennessee, Knoxville, TN (United States)] (ORCID:0000000186261276); Grzywacz, R. [Univ. of Tennessee, Knoxville, TN (United States); Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)] (ORCID:0000000209202587); Poves, A. [Univ. Autonoma de Madrid (Spain)] (ORCID:000000017539388X). DOE Contract: AC05-00OR22725; FG02-96ER40983; NA0003180; NA0003899; NA0003906; NA0004068; SC0020451. Subjects: 73 NUCLEAR PHYSICS AND RADIATION PHYSICS