Nuclear and Electronicg-Factors of²¹¹Fr, Nuclear Ground-State Spin of²⁰⁷Fr and the Nuclear Single-Particle Structure in the Range²⁰⁷⁻²²⁸Fr

The nuclear and electronic magnetic dipole moments of 21 Fr and the nuclear ground-state spin of 207 Fr have been measured directly by on-line atomic-beam magnetic resonance techniques at the ISOLDE facility at CERN. The following results have been obtained: μ I ( 211 Fr) = 4.00(8) nm, g J (Fr, 7 s 2 S 1/2 ) = 2.00497(9) and I ( 207 Fr) = 9/2. A large deviation of the electronic magnetic moment from the free electron value was found. Using the measured nuclear magnetic moment μ I ( 211 Fr), a comparison is made between different theoretical calculations of the magnetic dipole hyperfine constants and with the available experimental data in 211 Fr. An analysis of the electric quadrupole interaction is also given. Nuclear magnetic dipole and electric quadrupole moments are deduced for the sequences 207-213 Fr and 220-228 Fr, using the data on 211 Fr as reference values. The nuclear quantities are discussed within the framework of the shell model and the core-quasiparticle model, giving information on the nuclear single-particle structure and on the variation in deformation along the sequences of francium isotopes.