/pdf/laser-spectroscopy-for-the-study-of-exotic-nuclei-e74lz4uc.pdf

Laser spectroscopy for the study of exotic nuclei

This thesis presents nuclear spins, electromagnetic moments, and changes in the mean-square charge radii for radioactive gallium isotopes, and the latter two for the francium isotope 214Fr with additional α-decay spectroscopy. Measurements were made using the CRIS technique at the ISOLDE facility in CERN, facilitating some of the most sensitive nuclear structure studies on exotic nuclei to date. Where applicable, experimental results are compared to empirical, and LSSM calculations. The amalgamated data set has presented the opportunity of probing the sturdiness of three doubly-magic nuclei with respect to their local vicinities: 56Ni, 78Ni, and 208Pb. A magical 56Ni core is confirmed with an electromagnetic-moment analysis of 65,67,69Ga, albeit of a soft nature. Comparisons with shell model calculations not only confirm increased mixtures of π2p3/2/π1f5/2 configurations and the presence of neutron correlations towards N = 28, but they also highlight systematic trends with respect to the neighbouring odd-Z isotope chains. Analyses of neutron-rich species up to 82Ga reveal a rich collection of nuclearstructure effects: a gradual proton-occupation migration from π2p3/2 → π1f5/2 for the odd-A species which culminates in a ground-state spin reversal involving those spins at 81Ga, isomeric presence in 80Ga at N = 49, and a kink in the change in the mean-square charge radii for 82Ga at N = 51. Overall, this adds further evidence for a robust doubly magic 78Ni core. Measurements of 214Fr with t1/2 = 5 ms represents the shortest-lived isotope to have been measured with laser spectroscopy techniques at an online facility, in which the ISOL production mechanism is the limiting factor. With its g factor suggesting a relatively pure (π1h9/2 ⊗ ν2g9/2) configuration for I = 1− and a kink in its charge-radii value at N = 127, the magical effects of 208Pb can be observed five protons away.

Exploring the magical tenacity of doubly closed-core nuclei with gallium and francium isotopes

Offline 2 is an entirely new research and development mass separator laboratory for the ISOLDE facility located on the Meyrin site of CERN. It closely resembles beam production (for non-radioactive beams) of the on-line (radioactive) systems at ISOLDE with machine versatility and flexibility at the core of its design. The beam optics and down stream beam preparation can deliver bunched beams or continuous beams of negative or positive ions with kinetic energies up to 60 keV. The mass resolving power of the separator operating with a typical ISOLDE ion source is R ∼ 500 . All of this is housed within a highly accessible 125 m2 work area with multiple beam optics instruments to determine the beam quality, quantify modifications, develop new technologies and create alternate beam tunes, with the purpose of improving the beams and targets used during on-line operations.

Offline 2, ISOLDE's target, laser and beams development facility

Since 2001, the SPIRAL 1 facility has been one of the pioneering facilities in ISOL techniques for re-accelerating radioactive ion beams: the fragmentation of the heavy ion beams of GANIL on graphite targets and subsequent ionization in the Nanogan ECR ion source has permitted to deliver beams of gaseous elements (He, N, O, F, Ne, Ar, Kr) to numerous experiments. Thanks to the CIME cyclotron, energies up to 20 AMeV could be obtained. In 2014, the facility was stopped to undertake a major upgrade, with the aim to extend the production capabilities of SPIRAL 1 to a number of new elements. This upgrade, which is presently under commissioning, consists in the integration of an ECR booster in the SPIRAL 1 beam line to charge breed the beam of different 1+ sources. A FEBIAD source (the so-called VADIS from ISOLDE) was chosen to be the future workhorse for producing many metallic ion beams. This source was coupled to the SPIRAL 1 graphite targets and tested on-line with different beams at GANIL. The charge breeder is an upgraded version of the Phoenix booster which was previously tested in ISOLDE. It was recently commissioned at LPSC and lately in the SPIRAL 1 beam lines with stable beams. The upgrade additionally permits the use of other target material than graphite. In particular, the use of fragmentation targets will permit to produce higher intensities than from projectile fragmentation, and thin targets of high Z will be used for producing beams by fusion-evaporation. The performances of the aforementioned ingredients of the upgrade (targets, 1+ source and charge breeder) have been and are still being optimized in the frame of different European projects (EMILIE, ENSAR and ENSAR2). The upgraded SPIRAL 1 facility will provide soon its first new beams for physics and further beam development are undertaken to prepare for the next AGATA campaign. The results obtained during the on-line commissioning period permit to evaluate intensities for new beams from the upgraded facility. © 2001 Elsevier Science. All rights reserved.

New exotic beams from the SPIRAL 1 upgrade

Collinear Doppler-free 2-photon resonance ionization has been applied inside a hot cavity laser ion source environment at CERN-ISOLDE. An injection-seeded Ti:sapphire ring laser was used to generate light pulses with a Fourier-limited linewidth for high-resolution spectroscopy. Using a molybdenum foil as a reflective surface positioned at the end of the target transfer line, rubidium was successfully ionized inside the hot cavity. The results are presented alongside previously obtained data from measurements performed at the RISIKO mass separator at Mainz University, where collinear and perpendicular ionization geometries were tested inside an RFQ ion guide. This work is a pre-cursor to the application of the Doppler-free 2-photon in-source spectroscopy method at ISOLDE. This approach aims to take advantage of the unmatched sensitivity of in-source spectroscopy, without the disadvantage of Doppler broadening.

pdf/first-demonstration-of-doppler-free-2-photon-in-source-laser-4kowmw56s8.pdf

First demonstration of Doppler-free 2-photon in-source laser spectroscopy at the ISOLDE-RILIS

The Versatile Arc Discharge and Laser Ion Source (VADLIS) is a recently established ion source for the CERN-ISOLDE radioactive ion beam facility. It offers either electron-impact ionization (VADIS-mode) or resonance laser ionization (RILIS-mode). The choice of operating mode depends on the element of interest or the required beam purity. Particle-in-cell simulations using the VSim software show that the ion extraction efficiency of the VADLIS in RILIS-mode can be improved if it is equipped with an insulated extractor plate, to which an optimal voltage can be applied. This enables optimization of the RILIS-mode ion extraction independently of the electron density. Experiments have been performed using a prototype VADLIS with an adjustable extractor plate voltage for the generation of gallium ion beams at the off-line separator as well as magnesium, molybdenum and mercury ion beams at ISOLDE. A factor >2 increase of the VADLIS efficiency in RILIS-mode has been achieved.

Enhancing the extraction of laser-ionized beams from an arc discharge ion source volume

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Enhancing the extraction of laser-ionized beams from an arc discharge ion source volume