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The yrast band of the NϭZ nucleus 84 Mo has been extended up to the 10 ϩ state. Its moment of inertia varies smoothly up to this state ͑rotational frequency 0.6 MeV͒. The new data confirm the systematic delay of the particle alignment frequency in NϭZ nuclei with respect to the neighboring NϾZ nuclei, which has been suggested as a signature of the neutron-proton pairing interaction. Projected shell model calculations performed for the heaviest NϭZ nuclei studied so far, 84 Mo and 88 Ru, predict that the confirmation of a possible enhancement of the neutron-proton residual interaction requires the observation of still higher spins in these nuclei.The study of NϭZ nuclei is expected to give the most relevant information about the properties of the neutronproton (np) pairing interaction. In NϭZ nuclei, neutrons and protons occupy the same shell-model orbitals, and thus can have the largest probability to interact with each other. It has been thought that the np pairing interaction may be the cause of the delayed rotational alignments in the even-even NϭZ nuclei in the Aϳ80 mass region, and this line of research has been actively pursued. The recently observed alignment delays in 72 Kr, 76 Sr, and 80 Zr may be such examples ͓1,2͔.Experimentally, the main difficulty in extending the study of NϭZ nuclei at higher spins is their population with extremely low cross sections in a small number of available reactions. Progress in the development of large ␥-ray arrays and associated ancillary detectors, as well as refinements of the data processing techniques, allowed recent advance in the knowledge of the heaviest NϭZ nuclei in general, and of their high spin behavior in particular. Theoretically, it has been suggested that the behavior of the moment of inertia of an NϭZ nucleus with increasing spin ͑rotation͒ would be particularly relevant in this respect. Different pairing fields (nn, pp, and np) respond differently to the Coriolis forces. The enhancement of the np interaction in NϭZ nuclei has in general an effect to sustain the pairing field under rotation. The real situation is, however, rather complicated, due to the fact that the spin alignment is also sensitively influenced by other factors such as deformation. Theoretical calculations, most of which are still schematic, have reached various conclusions on the role of different np interactions ͓3-9͔.To date, consistent delays in the crossing frequencies ͑due to alignment of the g 9/2 particles͒ in the ground state bands have been observed for the NϭZ Kr ͓1,2͔, Sr, Zr ͓2͔, and Ru ͓10͔ nuclei. The strongest effect has been observed in 72 Kr where a very delayed crossing has been located at 0.85 MeV ͓2͔. In 76 Sr there is a discernible effect which indicates a broad crossing shifted to 0.62 MeV ͑compared to Ϸ0.55 in NϾZ isotopes ͓2͔͒, while for 80 Zr ͓2͔ and 88 Ru ͓10͔ the observations indicate again a delay but the crossing has not been located yet. In this chain of NϭZ nuclei, 84 Mo is the only one which has not been studied at spins higher than 4ប.In view of the pre...

Excited states in 52 Fe have been determined up to spin 10h in the reaction 28 Si + 28 Si at 115 MeV by using γ-ray spectroscopy methods at the GASP array. The excitation energy of the yrast 10 + state has been determined to be 7.381 MeV, almost 0.5 MeV above the well known β + -decaying yrast 12 + state, definitely confirming the nature of its isomeric character. The mean lifetimes of the states have been measured by using the Doppler Shift Attenuation method. The experimental data are compared with spherical shell model calculations in the full pf -shell.