New spin assignments in the odd-odd N=Z nucleus ⁴²Sc and the breaking of the ⁴⁰Ca core

Using the ⁴⁰Ca(³He,p) reaction at E_³He=9 MeV and the multidetector array HORUS, angular correlations of coincident pairs of γ transitions in the odd-odd N=Z nucleus ⁴²Sc have been measured at the FN tandem Van de Graaff accelerator of the University of Cologne. The analysis of the data allowed nine new spin assignments and the determination of a series of new multipole mixing ratios. In particular, the spin and parity of the 5⁺ and 7⁺ levels belonging to the lowest T=0πf_7/2νf_7/2 multiplet have been determined and the (6⁺) level from the T=1 multiplet has been tentatively assigned. In this way, all T=1 states up to an excitation energy of 3.2 MeV now have known spins as well as the lowest T=0 quadruplet (J^π=1⁺,3⁺,5⁺,7⁺) and many other T=0 states of unknown structure. The comparison with shell-model calculations reveals that a breaking of the ⁴⁰Ca core has to be invoked to describe the level structure of ⁴²Sc.