Nuclear Magnetic Moment of 59Cu with On-line $\beta$-NMR on Oriented Nuclei

The nuclear magnetic moment of the nucleus 59Cu with one proton and two neutrons outside the closed N = Z = 28 shells, was measured in an on-line experiment combining beta-NMR with low temperature nuclear orientation and with particle detectors operating at a temperature of about 10K. From the data the center frequency \nu(B_ext = 0) = 209.51(22) MHz was derived. Using the hyperfine field of Cu in host iron from literature the results for the moment is \mu[59Cu] = +1.891(9)\mu_N, wich reveals a large deviation from the proton p3/2 single-particle value. This provides strong experimental evidence for a massive shell breaking at 56Ni