Measurements consisting of γ-ray excitation functions and angular distributions have been performed using the (n, n ′ γ) reaction on 62 Ni. The excitation function data allowed us to check the consistency of the placement of transitions in the level scheme. From γ-ray angular distributions, the lifetimes of levels up to ∼ 3.8 MeV in excitation energy have been extracted with the Doppler-shift attenuation method. The experimentally deduced values of reduced transition probabilities have been compared with the predictions of the quadrupole vibrator model and with large-scale shell model calculations in the f p shell configuration space. Two-phonon states have been found to exist with some notable deviation from the predictions of the quadrupole vibrator model, but no evidence for the existence of three-phonon states could be established. Z = 28 proton core excitations play a major role in understanding the observed structure.

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Excited low-spin states of 92 Zr have been studied with the (n,n γ ) reaction. Comprehensive data on the electromagnetic decay of states with excitation energies up to about 3.8 MeV in particular, lifetimes, γ -ray branching ratios, multipole mixing ratios, and absolute transition strengths have been obtained. The detailed spectroscopic information about the low-spin level scheme enables us to address the predominant proton-neutron symmetry for low-spin states of 92 Zr. These data are compared to those of corresponding states in the N = 52 isotone 94 Mo and to a shell model calculation using 88 Sr as an inert core. However, neither a purely collective picture nor the restricted shell model calculation yields a fully satisfactory description of the observed structures. [1][2][3][4]. In neighboring 96 Ru 52 , the 2 + 1,ms state was found [5,6], and candidates for two-phonon MS states were assigned from E2/M1 mixing ratios, branching ratios, and lifetime limits [6].In vibrational nuclei, signatures of MS states, accessible through γ -ray spectroscopy at rather low excitation energies, are strong M1 transitions to symmetric states with the same phonon number with matrix elements of about | J f sym M1 J i ms | ≈ 1µ N , and weakly collective E2 transitions to symmetric states, since the latter transitions stem from the annihilation of a MS phonon Q ms . In contrast, we expect collective E2 transitions with transition strengths of several Weisskopf units between states with the same proton-neutron symmetry, e.g., from the MS two-phonon states to the 2 + 1,ms state from the annihilation of a symmetric phonon Q s . 0556-2813/2005/71(5)/054304(15)/$23.00 054304-1