Abstract
High-precision reduced electric-quadrupole transition probabilities B(E2) have been
measured from single-step Coulomb excitation of semi-magic 58,60,62,64 Ni (Z = 28) beams at 1.8 MeV per nucleon on a natural carbon target. The energy loss of the nickel beams through the carbon
target were directly measured with a zero-degree Bragg detector and the absolute B(E2) values
were normalized by Rutherford scattering. The B(E2) values disagree with recent lifetime studies
that employed the Doppler-shift attenuation method. The present high-precision B(E2) values
reveal an asymmetry about 62 Ni, midshell between N = 28 and 40, with larger values towards 56 Ni
(Z = N = 28). The experimental B(E2) values are compared with shell-model calculations in the
full pf model space and the results indicate a soft 56 Ni core.
