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

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Excited states in ;{152}Sm have been investigated with the ;{152}Sm(n,n;{'}gamma) reaction. The lowest four negative-parity band structures have been characterized in detail with respect to their absolute decay properties. Specifically, a new K;{pi} = 0;{-} band has been assigned with its 1;{-} band head at 1681 keV. This newly observed band has a remarkable similarity in its E1 transition rates for decay to the first excited K;{pi} = 0;{+} band at 684 keV to the lowest K;{pi} = 0;{-} band and its decay to the ground-state band. Based on these decay properties, as well as energy considerations, this new band is assigned as a K;{pi} = 0;{-} octupole excitation based on the K;{pi} = 0_{2};{+} state. An emerging pattern of repeating excitations built on the 0_{2};{+} level similar to those built on the ground state may indicate that ;{152}Sm is a complex example of shape coexistence rather than a critical point nucleus.

Low-lying multiphonon states in 136 Ba have been populated with the inelastic neutron scattering reaction. Excitation functions were performed at neutron energies from 2.2 to 3.9 MeV, and γ -ray angular distributions were measured at 2.5, 3.0, and 3.5 MeV. Lifetimes have been determined using the Doppler-shift attenuation method, and electromagnetic transition rates have been deduced. The previously assigned 2 + 1,ms mixed-symmetry state at 2128.9 keV has been confirmed and is not greatly fragmented. For the first time in the N = 80 isotones, a 3 + 2,ms two-phonon mixed-symmetry state is proposed. In addition, the 2 + 5 and the 4 + 3 levels at 2222.7 and 2356.4 keV, respectively, decay with large B(M1) values to the two-phonon 2 + 2 and 4 + 1 states, respectively, which suggests two-phonon mixed-symmetric character. Their excitation energies, however, are not consistent with this interpretation.