Electric Monopole Transition Strengths in⁶²Ni

Abstract

Abstract. Excited states in 62 Ni were populated with a (p, p') reaction using the 14UD Pelletron accelerator at the Australian National University. Electric monopole transition strengths, ρ 2 (E0), were measured through simultaneous detection of the internal conversion electrons and γ rays emitted from the de-excitation of populated states, using the Super-e spectrometer coupled with a germanium detector. The strength of the 0 + 2 to 0 + 1 transition has been measured to be 77 +23 −34 × 10 −3 and agrees with previously reported values. Upper limits have been placed on the 0 + 3 to 0 + 1 and 0 + 3 to 0 + 2 transitions. The measured ρ 2 (E0) value of the 2 + 2 to 2 + 1 transition in 62 Ni has been measured for the first time and found to be one of the largest ρ 2 (E0) values measured to date in nuclei heavier than Ca. The low-lying states of 62 Ni have previously been classified as one-and two-phonon vibrational states based on level energies. The measured electric quadrupole transition strengths are consistent with this interpretation. However as electric monopole transitions are forbidden between states which differ by one phonon number, the simple harmonic quadrupole vibrational picture is not sufficient to explain the large ρ 2 (E0) value for the 2 + 2 to 2 + 1 transition.

Critical insights into nuclear collectivity from complementary nuclear spectroscopic methods

“…A comprehensive study [84] performed with the (n, n′γ) reaction found that the twophonon states had notable deviations from the harmonic predictions, and there was no evidence for the existence of three-phonon states. Measurements [85,86] A very important step in the direction to understand the origin of collectivity in spherical or weakly-deformed nuclei was provided by Walz et al [87] in their pioneering study of 92 Zr by both electron and proton scattering. Their first result was that the collectivity in the + 2 1 state (and also the so-called 'mixed-symmetry' state) was predominately due to mixing with the giant quadrupole resonance (GQR).…”

“…Of the Sr isotopes, Kern et al [10] cited 82 Sr as the best example of spherical vibrational behaviour; however, they also cautioned that this agreement might be 'accidental'. Figure 38 displays the data for the low-lying states in the [80][81][82][83][84][85][86] Sr isotopes. Indeed, the level energies for 82 value point to a transition to a deformed structure.…”