Coulomb excitation of 31Mg

The ground state properties of 31Mg indicate a change of nuclear shape at N = 19 with a deformed Jπ = 1/2+ intruder state as a ground state, implying that 31Mg is part of the “island of inversion”. The collective properties of excited states were the subject of a Coulomb excitation experiment at REXISOLDE, CERN, employing a radioactive 31Mg beam. De-excitation γ -rays were detected by the MINIBALL γ -spectrometer in coincidence with scattered particles in a segmented Si-detector. The level scheme of 31Mg was extended. Spin and parity assignment of the 945 keV state yielded 5/2+ and its de-excitation is dominated by a strong collective M1 transition. Comparison of the transition probabilities of 30,31,32Mg establishes that for the N = 19 magnesium isotope not only the ground state but also excited states are largely dominated by a deformed pf intruder configuration.status: publishe