ATMR investigation of quadrupole order parameter in actinide dioxides

O-17-NMR have been performed to investigate the order parameters in actinide dioxides. In the antiferro-magnetic ordered state Of UO2, magnetic dipole and electric quadrupole order parameters have been extracted individually through the microscopic hyperfine interactions with O-17 nuclei. We have also detected the development of the quadrupole order parameter in the exotic multipolar ordering state of NpO2. The large value of the critical exponent suggests the secondary character of the quadrupole ordering in NpO2.