  The 1789 keV level in 30Mg was identified as the first excited 0^+ state by
measuring its E0 transition to the ground state. The measured small value of
rho^2(E0,0^+_2 --> 0^+_1) = 5.7(14) x 10^-3 implies a very small mixing of
competing configurations with largely different intrinsic quadrupole
deformation near N=20. Axially symmetric Beyond-Mean-Field 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 a two neutrons excitated into the nu1 f_{7/2} orbital. Using a
two-level model, a mixing amplitude of 0.08(4) can be derived.
