Electric monopole transition strengths in 62Ni

Abstract

Excited states in 62Ni were populated with a (p, p') reaction using the 14UD Pelletron accelerator at the Australian National University. Electric monopole transition strengths, ρ2(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 ρ2(E0) value of the 2+ 2 to 2+ 1 transition in 62Ni has been measured for the first time and found to be one of the largest ρ2(E0) values measured to date in nuclei heavier than Ca. The low-lying states of 62Ni 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 ρ2(E0) value for the 2+ 2 to 2+ 1 transition