Intruder features in the island of inversion: The case of Mg-33

The Na-33 beta decay was studied online using mass separation techniques and a first description of the level structure of the neutron-rich isotope Mg-33, with N=21, has been obtained. The experiment involved the measurement of beta-gamma, beta-gamma-gamma, and beta -n-gamma coincidences as well as neutron spectra by time-of-flight technique. The first low energy level scheme for the daughter nucleus Mg-33 is given with five bound states. Spin and parity assignments are proposed according to beta feedings and gamma -ray multipolarities, beta -strength distribution is evaluated, taking into account 1n- and 2n-emission channels and it is compared with the calculated GT strength distribution. In particular, the 1p-1h and 2p-2h excitations are shown to result in substantial contribution to the low energy configurations. Allowed beta branch to the (33)Ma g.s. [log ft = 5.27(26)] gives direct evidence for the inversion of nu (f(7/2)) and nu (d(3/2)) states.