Shape coexistence in 68Ni

The internal-conversion and internal-pair-production decays of the first excited 0(+) state in Ni-68 are studied following the beta decay of Co-68. A novel experimental technique, in which the ions of Co-68 were implanted into a planar germanium double-sided strip detector and which required digital pulse processing, is developed. The values for the energy of the first excited 0(+) state and the electric monopole transition strength from the first excited 0(+) state to the ground state in Ni-68 are determined to be 1605(3) keV and 7.6(4) x 10(-3), respectively. Comparisons of the experimental results to Monte Carlo shell-model calculations suggest the coexistence between a spherical ground state and an oblate first excited 0(+) state in Ni-68.