The Na-33 beta decay was studied online using mass separation techniques an
d 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 sch
eme for the daughter nucleus Mg-33 is given with five bound states. Spin an
d parity assignments are proposed according to beta feedings and gamma -ray
multipolarities, beta -strength distribution is evaluated, taking into acc
ount 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 configuration
s. 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.