R. Catherall

Pulse shape of the ISOLDE radioactive ion beams

Abstract The 2.4 μs proton pulses from the PS Booster are delivered to the ISOLDE targets at a low repetition rate (typically 0.4 Hz). However, the synchronously produced radioisotopes have partially lost this time structure due to the delay incurred by the mass transfer processes used in their conversion into an ion beam. Since the pulse shape of the ion bunches is a vital information for the target development and the experiments, new techniques have been developed to measure it. These methods as well as the mathematics used for calculating the production yield will be described in detail. The limits of the techniques are discussed and a set of examples are presented.

Recent developments of the ISOLDE laser ion source

The ISOLDE laser ion source (LIS), in which stepwise resonant laser ionization is performed inside a high-temperature cavity, has been extended to include the elements Be, Zn, Cu and Cd. The ionization efficiencies obtained are discussed with respect to the level of saturation of each step achieved with the available laser beam intensities. Because of a high ionization potential of about 9 eV the first resonant transition of Be, Zn and Cd is in the far ultraviolet (UV) region. The UV laser beam needed for the first resonant step of Be, Zn and Cd is achieved in a new laser setup via frequency tripling of the dye laser light. The ions created during the 30 ns laser pulse are extracted from the hot cavity of the ion source by the electrical field resulting from the ohmic heating of the cavity. The time distribution of the laser-ionized ion bunches was measured for various cavities and temperatures. The time structure of the ion bunch is discussed in order to gain insight into the development of LIS cavities.

On-line yields obtained with the ISOLDE RILIS

The ISOLDE resonance ionization laser ion source (RILIS) allows to ionize efficiently and selectively many metallic elements. In recent yield surveys and on-line experiments with the ISOLDE RILIS we observed 23–34 Mg, 26–34 Al, 98–132 Cd, 149 Tb, 155–177 Yb, 179–200 Tl, 183–215 Pb and 188–218 Bi. The obtained yields are presented together with measured release parameters which allow to extrapolate the release efficiency towards more exotic (short-lived) nuclides of the same elements. 2002 Elsevier Science B.V. All rights reserved.

Development of high efficiency Versatile Arc Discharge Ion Source at CERN ISOLDE

We report here recent developments of Forced Electron Beam Induced Arc Discharge (FEBIAD) ion sources at the ISOLDE radioactive ion beam facility, hosted at the European Organization for Nuclear Research (CERN). As a result of the propositions to improve the ionization efficiency, two FEBIAD prototypes have been produced and successfully tested in 2008. Off-line studies showed that the 1+ ionization efficiencies for noble gases are 5-20 times larger than with the standard ISOLDE FEBIAD ion sources and reach 60% for radon, which allowed the identification at ISOLDE of (229)Rn, an isotope that had never previously been observed in the laboratory. A factor of 3 increase is also expected for the ionization efficiency of the other elements. The experimental and theoretical methodology is presented. The theoretical model, which gives precise insights on the processes affecting the ionization, is used to design optimal sources (grouped under the name of VADIS--Versatile Arc Discharge Ion Source) for the different chemical classes of the produced isotopes, as already demonstrated for the noble gases.

Release from ISOLDE molten metal targets under pulsed proton beam conditions

Abstract By moving the ISOLDE mass separators from the 600 MeV Synchrocyclotron (SC) to the 1 GeV Proton-Synchrotron-Booster (PS) [1] the instantaneous energy density of the proton beam went up by 3 orders of magnitude. The developments of the molten metal target units and the optimization of the PS proton beam to cope with the effects of the thermal shocks induced by the proton beam are described. The energy density of the PS proton beam was reduced by spatial defocusing and time staggered extraction of the four PS-accelerators. The release from lanthanum, lead and tin targets is discussed for different settings of the proton beam and compared to the release observed at ISOLDE-SC. The yields of Hg isotopes are presented.

Release and yields from thorium and uranium targets irradiated with a pulsed proton beam

Abstract Radioactive ion-beams produced from various uranium and thorium targets at the ISOLDE mass separator facility are presented. The targets are bombarded with 1 GeV protons delivered by the PS-Booster at CERN. The target materials are uranium carbide and thorium carbide, both prepared from the oxides or diphtalocyanines of uranium and thorium. Due to the pulsed structure of the PS-Booster, release can be measured as a function of time for a number of elements. Beam intensities and delay time distributions of the alkali-metals, the earth-alkalis, the boron group and the noble gases measured from the described targets are discussed. Comparisons are made between the target materials and with ISOLDE beam intensities produced by 600 MeV protons from the CERN synchrocyclotron.

Production of radioactive Ag ion beams with a chemically selective laser ion source

Abstract We have developed a chemically selective laser ion source at the CERN-ISOLDE facility in order to study neutron-rich Ag nuclides. A pulsed laser system with high repetition rate has been used based on high-power coppe-vapour pump lasers and dye lasers. With this source significant reductions of the isobaric background has been achieved.

Oxide fiber targets at ISOLDE

Abstract Many elements are rapidly released from oxide matrices. Some oxide powder targets show a fast sintering, thus losing their favorable release characteristics. Loosely packed oxide fiber targets are less critical since they may maintain their open structure even when starting to fuse together at some contact points. The experience with various oxide fiber targets (titania, zirconia, ceria and thoria) used in the last years at ISOLDE is reviewed. For short-lived isotopes of Cu, Ga and Xe the zirconia and ceria targets respectively provided significantly higher yields than any other target (metal foils, oxide powders, etc.) tested before. Titania fibers, which were not commercially available, were produced in a relic process by impregnation of a rayon felt in a titanium chloride solution and subsequent calcination by heating the dried felt in air. Thoria fibers were obtained either by the same process or by burning commercial gas lantern mantle cloth. In the future a beryllia fiber target could be used to produce very intense 6He beams (order of 1013 ions per second) via the 9Be(n,α) reaction using spallation neutrons.

Off-line production of intense 7,10Be+ beams

Abstract 7 Be and 10 Be were produced by 590 MeV proton bombardment of a graphite target at PSI. Parts of this graphite target were transferred into an ISOLDE target and ion source unit and ionized with the ISOLDE resonance ionization laser ion source. Thus intense radioactive ion beams of 300 nA of 7,10 Be + were produced off-line.

Recent developments in production of radioactive ion beams with the selective laser ion source at the on-line isotope separator ISOLDE

The resonance ionization laser ion source (RILIS) of the ISOLDE on-line isotope separation facility is based on the method of laser stepwise resonance ionization of atoms in a hot metal cavity. The atomic selectivity of the RILIS compliments the mass selection process of the ISOLDE separator magnets to provide beams of a chosen isotope with greatly reduced isobaric contamination. Using a system of dye lasers pumped by copper vapor lasers, ion beams of 22 elements have been generated at ISOLDE with ionization efficiencies in the range of 0.5%–30%. As part of the ongoing RILIS development, recent off-line resonance ionization spectroscopy studies have determined the optimal three-step ionization schemes for yttrium, scandium, and antimony.