T. Gottwald

The laser ion source trap for highest isobaric selectivity in online exotic isotope production

The improvement in the performance of a conventional laser ion source in the laser ion source and trap (LIST) project is presented, which envisages installation of a repeller electrode and a linear Paul trap/ion guide structure. This approach promises highest isobaric purity and optimum temporal and spatial control of the radioactive ion beam produced at an online isotope separator facility. The functionality of the LIST was explored at the offline test separators of University of Mainz (UMz) and ISOLDE/CERN, using the UMz solid state laser system. Ionization efficiency and selectivity as well as time structure and transversal emittance of the produced ion beam was determined. Next step after complete characterization is the construction and installation of the radiation-hard final trap structure and its first online application.

GISELE: A resonant ionization laser ion source for the production of radioactive ions at GANIL

SPIRAL2 is the new project under construction at GANIL to produce radioactive ion beams and in particular neutron rich ion beams. For the past 10 yr SPIRAL1 at GANIL has been delivering accelerated radioactive ion beams of gases. Both facilities now need to extend the range of radioactive ion beams produced to condensable elements. For that purpose, a resonant ionization laser ion source, funded by the French Research National Agency, is under development at GANIL, in collaboration with IPN Orsay, University of Mainz (Germany) and TRIUMF, Vancouver (Canada). A description of this project called GISELE (GANIL Ion Source using Electron Laser Excitation) is presented.

An All-Solid-State High Repetiton Rate Titanium:Sapphire Laser System For Resonance Ionization Laser Ion Sources

On‐line production facilities for radioactive isotopes nowadays heavily rely on resonance ionization laser ion sources due to their demonstrated unsurpassed efficiency and elemental selectivity. Powerful high repetition rate tunable pulsed dye or Ti:sapphire lasers can be used for this purpose. To counteract limitations of short pulse pump lasers, as needed for dye laser pumping, i.e. copper vapor lasers, which include high maintenance and nevertheless often only imperfect reliability, an all‐solid‐state Nd:YAG pumped Ti:sapphire laser system has been constructed. This could complement or even replace dye laser systems, eliminating their disadvantages but on the other hand introduce shortcomings on the side of the available wavelength range. Pros and cons of these developments will be discussed.

Resonance ionization spectroscopy of thorium isotopes?towards a laser spectroscopic identification of the low-lying 7.6 eV isomer of 229Th

In-source resonance ionization spectroscopy was used to identify an efficient and selective three-step excitation/ionization scheme of thorium, suitable for titanium:sapphire (Ti:sa) lasers. The measurements were carried out in the preparation of laser spectroscopic investigations for an identification of the low-lying 229mTh isomer predicted at 7.6 ± 0.5 eV above the nuclear ground state. Using a sample of 232Th, a multitude of optical transitions leading to over 20 previously unknown intermediate states of even parity as well as numerous high-lying odd parity auto-ionizing (AI) states were identified. Level energies were determined with an accuracy of 0.06 cm−1 for intermediate and 0.15 cm−1 for AI states. Using different excitation pathways, an assignment of total angular momenta for several energy levels was possible. One particularly efficient ionization scheme of thorium, exhibiting saturation in all three optical transitions, was studied in detail. For all three levels in this scheme, the isotope shifts of the isotopes 228Th, 229Th and 230Th relative to 232Th were measured. An overall efficiency including ionization, transport and detection of 0.6% was determined, which was predominantly limited by the transmission of the mass spectrometer ion optics.

Ion production from solid state laser ion sources.

Laser ion sources based on resonant excitation and ionization of atoms are well-established tools for selective and efficient production of radioactive ion beams. Recent developments are focused on the use of the state-of-the-art all solid-state laser systems. To date, 35 elements of the periodic table are available from laser ion sources based on tunable Ti:sapphire lasers. Recent progress in this field regarding the establishment of suitable optical excitation schemes for Ti:sapphire lasers are reported.

Emittance characterization of a hot-cavity laser ion source at Holifield Radioactive Ion Beam Facility

The first investigation of the transverse emittance of a hot-cavity laser ion source based on all-solid-state Ti:sapphire lasers is presented. The emittances of (63)Cu ion beams generated by three-photon resonant ionization are measured and compared with that of the (69)Ga and (39)K ion beams resulting from surface ionization in the same ion source. A self-consistent unbiased elliptical exclusion method is adapted for noise reduction and emittance analysis. Typical values of the rms and 90% fractional emittances of the Cu ion beams at 20 keV energy are found to be about 2 and 8 pi mm mrad, respectively, for the ion currents of 2-40 nA investigated. The emittances of the laser-produced Cu ion beams are smaller than those of the surface-ionized Ga and K ion beams.

Laser Resonance Ionization Spectroscopy of the Lanthanides Tb, Dy and Ho as Homologues to Actinides and Super Heavy Elements

Spectroscopic investigations of the rare earth elements Tb, Dy and Ho have been carried out using laser resonance ionization mass spectroscopy. A variety of new intermediate energy levels and autoionizing states were observed in these elements. Efficient and selective excitation and ionization schemes for the elements have been developed for Ti:Sapphire lasers using the spectroscopic data. Resonant ionization schemes for Np were also been studied as the preparation work for related investigations on actinide elements and for the spectroscopy on the heaviest elements, where spectroscopic data so far are scarce or not existing at all.

Depletion of the excited state population in negative ions using laser photodetachment in a gas-filled RF quadrupole ion guide

The depopulation of excited states in beams of negatively charged carbon and silicon ions was demonstrated using collisional detachment and laser photodetachment in a radio-frequency quadrupole ion guide filled with helium. The high-lying, loosely bound 2D excited state in C− was completely depleted through collisional detachment alone, which was quantitatively determined within 6%. For Si− the combined signal from the population in the 2P and 2D excited states was only partly depleted through collisions in the cooler. The loosely bound 2P state was likely to be completely depopulated, and the more tightly bound 2D state was partly depopulated through collisions. 98(2)% of the remaining 2D population was removed by photodetachment in the cooler using less than 2 W laser power. The total reduction of the excited population in Si−, including collisional detachment and photodetachment, was estimated to be 99(1)%. Employing this novel technique to produce a pure ground state negative ion beam offers possibilities of enhancing selectivity, as well as accuracy, in high-precision experiments on atomic as well as molecular negative ions.

Laser ion source development at Holifield Radioactive Ion Beam Facility

This report describes the efforts made to develop a resonant-ionization laser ion source based on tunable Ti:sapphire lasers for nuclear physics and astrophysics research at Holifield Radioactive Ion Beam Facility. Three Ti:sapphire lasers have been upgraded with individual pump lasers to eliminate laser power losses due to synchronization delays. Ionization schemes for 14 elements have been obtained. Off-line studies show that the overall efficiency of the laser ion source can be as high as 40%. TaC surface coatings have been investigated for minimizing surface and bulk trapping of the atoms of interest.

Time profile of ion pulses produced in a hot-cavity laser ion source

The time spreads of Mn ions produced by three-photon resonant ionization in a hot-cavity laser ion source are measured. A one-dimensional ion-transport model is developed to simulate the observed ion time structures. Assuming ions are generated with a Maxwellian velocity distribution and are guided by an axial electric field, the predictions of the model agree reasonably well with the experimental data and suggest that the ions are radially confined in the ion source and a substantial fraction of the ions in the transport tube are extracted.