DELAYED G(9 2)(2) ALIGNMENT IN THE N=Z NUCLEUS KR-72/

The structure of Kr-72 has been investigated at GASP through the Ca-40 (Ca-40,2 alpha) reaction at a beam energy of 160 MeV using the 4 pi IS IS Si-ball for reaction channel selection. The level scheme has been e xtended up to an excitation energy of approximate to 8.5 MeV. The spin s and parities of the observed levels are assigned tentatively. The ob served band shows the predicted change from oblate to prolate shape. T he four quasi-particle g(9/2) alignment is found to be significantly d elayed in rotational frequency with respect to the heavier Kr isotopes . Such a delay contradicts the predictions of standard mean-field calc ulations and may reflect either additional correlations in the T = 0 p airing channel or coupling to vibrational degrees of freedom or both. (C) 1997 Elsevier Science B.V.