The electric quadrupole moment and the magnetic moment (or the factor) of low-lying states in even-even nuclei 72-80Ge and odd-mass nuclei 75-79Ge are studied in the framework of the nucleon pair approximation (NPA) of the shell model, assuming the monopole and quadrupole pairing plus quadrupole-quadrupole interaction. Our calculations reproduce well the experimental values of and for 72,74,76Ge, as well as the yrast energy levels of these isotopes. The structure of the states and the contributions of the proton and neutron components in and are discussed in the -pair truncated shell-model subspace. The overall trend of and as a function of the mass number , as well as their signs, are found to originate essentially from the proton contribution. The negative value of in 72,74Ge is suggested to be due to the enhanced quadrupole-quadrupole correlation and configuration mixing.

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