In-source resonant ionization laser spectroscopy of the even-A polonium isotopes (192-210,216,218)Po has been performed using the 6p(3)7s (5)S(2) to 6p(3)7p (5)P(2) (λ=843.38  nm) transition in the polonium atom (Po-I) at the CERN ISOLDE facility. The comparison of the measured isotope shifts in (200-210)Po with a previous data set allows us to test for the first time recent large-scale atomic calculations that are essential to extract the changes in the mean-square charge radius of the atomic nucleus. When going to lighter masses, a surprisingly large and early departure from sphericity is observed, which is only partly reproduced by beyond mean field calculations.

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Hyperfine splitting parameters have been measured for the neutron-deficient odd-mass polonium isotopes and isomers [193][194][195][196][197][198][199][200][201][202][203] Po g,m , 209,211 Po. The measurement was performed at the ISOLDE (CERN) online mass separator using the in-source resonance ionization spectroscopy technique. The magnetic dipole moments μ and spectroscopic electric quadrupole moments Q S have been deduced. Their implication for the understanding of nuclear structure in the vicinity of the closed proton shell at Z = 82 and the neutron mid-shell at N = 104 is discussed. For the most neutron-deficient nuclei (A = 193,195,197), a deviation of μ and Q S from the nearly constant values for heavier polonium nuclei was observed. Particle-plus-rotor calculations with static oblate deformation describe the electromagnetic moments for these nuclei well, provided a gradual increase of a mean deformation when going to lighter masses is assumed for the polonium nuclei with A<198.

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The B(E2; 0 + → 2 + ) value in 68 Ni has been measured using Coulomb excitation at safe energies. The 68 Ni radioactive beam was postaccelerated at the CERN on-line isotope mass separator (ISOLDE) facility to 2.9 MeV/u and directed to a 108 Pd target. The emitted γ rays were detected by the MINIBALL detector array. Not only directly registered but also indirectly deduced information on the nucleus emitting the γ ray was used to perform the Doppler correction, leading to a larger center-of-mass angular range to infer the excitation cross section. orbitals. More recent mass measurements do show a local weak discontinuity in the two-neutron separation energy, thus confirming the very weak N = 40 subshell gap [5]. Still, the 68 Ni nucleus possesses nuclear properties that are characteristic for a doubly magic nucleus: a high 2 + energy and a low B(E2; 0 + → 2 + ) value [6,7,8,9,10]. In recent work it has been advocated that the high 2 + energy is largely due to the opposite parity of the ν2p 3 2 1f 5 2 2p 1 2 orbitals and the νg 9/2 orbital and that a major part of the B(E2) strength resides at high energy [11,12]. Although the high energy of the first 2 + state at 2033 keV has been measured by different experiments [1, 2, 3], the low B(E2; 0 + → 2 + ) value has been obtained from one Coulomb excitation experiment performed in inverse kinematics and using a 68 Ni beam at intermediate energy (produced from the fragmentation of a 70 Zn beam with an energy of 65.9 MeV/u). The value obtained was 255±60 e 2 fm 4 [3], approximately 2 times lower than the B(E2; 0 + → 2 + ) in 56 Ni, with Z = N = 28. As this low B(E2; 0 + → 2 + ) value is crucial for understanding the structure of 68 Ni, a new experiment aimed at measuring this value was performed using a postaccelerated 68 Ni beam from the CERN on-line isotope mass separator (ISOLDE) facility.In this note, we report on a determination of the B(E2; 0 + → 2 + ) value of 68 Ni using safe Coulomb excitation where the contribution of nuclear effects in the excitation process is limited because the separation between the surfaces of the colliding nuclei does not drop below 5 fm over the detected scattering range [13]. The 68 Ni (T 1/2 = 29 s) ion beam was produced at the ISOLDE radioactive-beam facility by bombarding a 1.4-GeV proton beam, produced by the PS booster accelerator, on a UC x target of 52 g/cm 2 . After diffusion of the fission products from the target and transport to the ion source, the nickel atoms were selectively laser ionized [14,15,16] and mass separated, yielding an average beam intensity of approximately 2.5 × 10 6 particles per second at 60 keV [17]. Subsequently, the beam was postaccelerated by up to an energy of 2.9 MeV/u. Coulomb excitation was induced by directing the postaccelerated 68 Ni beam at v/c ∼ 0.08 to a 2 mg/cm 2 108 Pd target. The scattered nuclei were detected by a double sided silicon strip detector (DSSSD) [19], consisting of