title: Shape coexistence near neutron number N=20: first identification of the E0 decay from the deformed first excited Jpi=0+ state in 30Mg.
abstract: The 1789 keV state in 30Mg was identified as the first excited 0+ state via its electric monopole (E0) transition to the ground state. The measured small value of rho2(E0,0(2)+-->0(1)+)=(26.2+/-7.5)x10(-3) implies within a two-level model a small mixing of competing configurations with largely different intrinsic quadrupole deformation near the neutron shell closure at N=20. Axially symmetric configuration mixing calculations identify the ground state of 30Mg to be based on neutron configurations below the N=20 shell closure, while the excited 0+ state mainly consists of two neutrons excited into the nu 1f7/2 orbital. The experimental result represents the first case where an E0 back decay from a strongly deformed second to the normal deformed first nuclear potential minimum well has been unambiguously identified, thus directly proving shape coexistence at the borderline of the much-debated "island of inversion."
authors: Ludwig-Maximilians-Universität München, D-85748 Garching, Germany.
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