In this Letter, we report a new mass for 11Li using the trapping experiment TITAN at TRIUMF's ISAC facility. This is by far the shortest-lived nuclide, t_{1/2}=8.8 ms, for which a mass measurement has ever been performed with a Penning trap. Combined with our mass measurements of ;{8,9}Li we derive a new two-neutron separation energy of 369.15(65) keV: a factor of 7 more precise than the best previous value. This new value is a critical ingredient for the determination of the halo charge radius from isotope-shift measurements. We also report results from state-of-the-art atomic-physics calculations using the new mass and extract a new charge radius for 11Li. This result is a remarkable confluence of nuclear and atomic physics.

Abstract. The Miniball germanium detector array has been operational at the REX (Radioactive ion beam EXperiment) post accelerator at the Isotope Separator On-Line facility ISOLDE at CERN since 2001. During the last decade, a series of successful Coulomb excitation and transfer reaction studies have been performed with this array, utilizing the unique and high-quality radioactive ion beams which are available at ISOLDE. In this article, an overview is given of the technical details of the full Miniball setup, including a description of the γ-ray and particle detectors, beam monitoring devices and methods to deal with beam contamination. The specific timing properties of the REX-ISOLDE facility are highlighted to indicate the sensitivity that can be achieved with the full Miniball setup. The article is finalized with a summary of some physics highlights at REX-ISOLDE and the utilization of the Miniball germanium detectors at other facilities.

The first excited 2 state of the unstable isotope 110 Sn has been studied in safe Coulomb excitation at 2:82 MeV=u using the MINIBALL array at the REX-ISOLDE post accelerator at CERN. This is the first measurement of the reduced transition probability of this state using this method for a neutron deficient Sn isotope. The strength of the approach lies in the excellent peak-to-background ratio that is achieved. The extracted reduced transition probability, BE2 : 0 ! 2 0:220 0:022e 2 b 2 , strengthens the observation of the evolution of the BE2 values of neutron deficient Sn isotopes that was observed recently in intermediate-energy Coulomb excitation of 108 Sn. It implies that the trend of these reduced transition probabilities in the even-even Sn isotopes is not symmetric with respect to the midshell mass number A 116 as 100 Sn is approached. DOI: 10.1103/PhysRevLett.98.172501 PACS numbers: 23.20.Js, 21.60.Cs, 25.70.De, 27.60.+j Substantial interest has recently arisen in the shell structure of atomic nuclei with only a few nucleons outside the double shell closure at 100 Sn. As an example, a series of experiments aiming at isotopes in this region has been carried out using fusion-evaporation reactions in the recent past [1]. With the advent of radioactive ion beams these studies are now taken further using sub-barrier and intermediate-energy Coulomb excitation [2,3]. In this Letter we present the only sub-barrier or ''safe'' Coulomb excitation experiment in this region to date. The study of the reduced transition probability -the BE2-of the first excited 2 state in an even-even nucleus gives a direct handle on the collectivity of that state. It can thus be used to measure systematic changes in the strengths of shell gaps. The general motivation for this kind of study goes back to our incomplete knowledge of the mechanisms that govern shell formation and their implications for the structure of nuclei far from stability. It is well known that a strong spinorbit force was introduced into the nuclear shell-model on Fermi's suggestion by Goeppert Mayer [4] and independently by Haxel, Jensen, and Suess [4] to explain the observed shell gaps. However, these papers were substantially predated by the consideration of a nuclear spin-orbit force by Inglis [5] who noted that the relativistic Thomas term which arises as a consequence of the noncommutation of Lorentz transformations should act also in atomic nuclei. This term, given by the vector product of the velocity and acceleration of the bound nucleon, gives rise to nuclear LS coupling, a result which can be derived from the Dirac equation [6]. In this picture, the acceleration is proportional to the derivative of the potential experienced by the bound particle, a notion still used in mean-field approaches today. As a consequence, the splitting of the shell gaps becomes density dependent and may change with the PRL 98,

A high-precision Penning trap mass measurement of the exotic 8He nuclide (T(1/2)=119 ms) has been carried out resulting in a reduction of the uncertainty of the halo binding energy by over an order of magnitude. The new mass, determined with a relative uncertainty of 9.2 x 10(-8) (deltam=690 eV) is 13 keV less bound than the previously accepted value. The mass measurement is of great relevance for the recent charge-radius measurement of 8He [P. Mueller, Phys. Rev. Lett. 99, 252501 (2007).10.1103/PhysRevLett.99.252501]. The 8He mass is the first result from the newly-commissioned Penning trap: TITAN (TRIUMF's Ion Trap for Atomic and Nuclear science) at the ISAC (Isotope Separator and Accelerator) radioactive beam facility at TRIUMF.

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Modern experiments at isotope separator on-line (ISOL) facilities like ISAC at TRIUMF often depend critically on the purity of the delivered rare isotope beams. Therefore, highly selective ion sources are essential. This article presents the development and successful on-line operation of an ion guide laser ion source (IG-LIS) for the production of ion beams free of isobaric contamination. Thermionic ions from the hot ISOL target are suppressed by an electrostatic potential barrier, while neutral radio nuclides effusing out are resonantly ionized by laser radiation within a quadrupole ion guide behind this barrier. The IG-LIS was developed through detailed thermal and ion optics simulation studies and off-line tests with stable isotopes. In a first on-line run with a SiC target a suppression of surface-ionized Na contaminants in the ion beam of up to six orders of magnitude was demonstrated.

We report on the first radioactive beam experiment performed at the recently commissioned REX-ISOLDE facility at CERN in conjunction with the highly efficient gamma spectrometer MINIBALL. Using 30Mg ions accelerated to an energy of 2.25 MeV/u together with a thin (nat)Ni target, Coulomb excitation of the first excited 2+ states of the projectile and target nuclei well below the Coulomb barrier was observed. From the measured relative deexcitation gamma-ray yields the B(E2;0(+)gs-->2(+)1) value of 30Mg was determined to be 241(31)e2 fm4. Our result is lower than values obtained at projectile fragmentation facilities using the intermediate-energy Coulomb excitation method, and confirms the theoretical conjecture that the neutron-rich magnesium isotope 30Mg resides outside the "island of inversion."