A.-H. Evensen

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.

CHEMICALLY SELECTIVE LASER ION SOURCE OF MANGANESE

Abstract Ion beams produced by on-line isotope separators are often contaminated by abundantly produced isobars. This significantly complicates, and in a number of cases renders impossible, the realization of physical experiments with such beams. In many cases the purity of the ion beams may be improved on the ionization stage of the isotope separation using a laser resonance ion source. The method of laser resonance ionization of atoms in a hot cavity has been applied for chemically selective production of Mn ion beams at the CERN-ISOLDE facility. Radiation of pulsed dye lasers and copper vapor lasers provided three-step excitation and ionization of Mn isotopes in the ordinary W surface ionizer, connected to the target container. High values of efficiency and selectivity obtained with the laser ion source made it possible to suppress substantially an admixture of 57 Fe in the 57 Mn ion beam and to perform Mossbauer experiments on implanted impurities in solids.

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.

Selective laser ionization of radioactive Ni-isotopes

Abstract A chemically selective laser ion source based on resonance ionization of atoms in a hot cavity has been applied in the study of Ni-isotopes at the CERN-ISOLDE on-line isotope separator. Laser ionization enhanced the yields of long-lived Ni-isotopes almost four orders of magnitude when compared to the yields obtained with the surface ionization mode of the source. As a result, high yields of long-lived Ni-isotopes were obtained. Separation efficiencies of 0.3 and 0.8% were obtained for Ni produced in uranium-carbide, produced from uranium-di-pthalocyanine, and Ta-foil targets, respectively. Ni was found to be released very slowly from the present target and ion source combination.

A new pulsed release method for element selective production of neutron rich isotopes near 208Pb

Abstract A new method to reduce the isobaric contamination problem for the production of neutron rich Bi, Pb and Tl nuclei at on-line mass separators, based on the pulsed release of these radioactive species, is presented. The results of a feasibility study are reported.

Bunched release of gases from oxide targets

Abstract Targets made out of oxides of the alkaline earth metals have been shown at ISOLDE to be among the fastest targets for production of radioactive beams of the rare gas elements. In addition oxide target materials release nitrogen and seem to be the only ones which may release the element carbon due to its oxidation to the high temperature stable CO gas. Thick targets of MgO and CaO have been studied in connection with their use at the 1GeV pulsed proton beam from the PS-BOOSTER synchrotron. It is shown that the 2.4 μs short proton pulse causes a pronounced bunched release with short delay of these elements which gives rise to 100–200 ms wide pulses of radioactive ion beams. Pulse shapes and overall yields of ion beams of He, Ne and Ar isotopes are studied as function of temperature and proton pulse intensity. For carbon and nitrogen also the release as function of the observed ionic species C+, CO+, N+ and N2+ is discussed.

Status of the REX-ISOLDE project

The Radioactive beam Experiment (REX-ISOLDE)(1,2,3) at ISOLDE/CERN is under progress and first tests are carried out with some of the structures. The radioactive ions from the online mass separator ISOLDE will be cooled and bunched in a Penning trap, charge bred in an electron beam ion source (EBIS) and finally accelerated in a short LINAC to a target energy between 0.8 and 2.2 MeV/u. The LINAC consists of a radio frequency quadrupole (RFQ) accelerator, which accelerates the ions up to 0.3 MeV/u, an interdigital H-type (IH) structure with a final energy between 1.1 and 1.2 MeV/u and three seven gap resonators, which allow the variation of the final energy. All components of the experiment are now in production or undergo first test measurements. Such measurements are ion capture tests of the trap, electron beam tests of the EBIS, low level measurements and first power tests of the RFQ and the first 7-gap resonator. In this paper the status of the experiment, and the proposed schedule are presented.

THE EVOLUTION OF THE ISOLDE CONTROL SYSTEM

Abstract The ISOLDE on-line mass separator facility is operating on a Personal Computer based control system since spring 1992. Front End Computers accessing the hardware are controlled from consoles running Microsoft Windows™ through a Novell NetWare4™ local area network. The control system is transparently integrated in the CERN wide office network and makes heavy use of the CERN standard office application programs to control and to document the running of the ISOLDE isotope separators. This paper recalls the architecture of the control system, shows its recent developments and gives some examples of its graphical user interface.

Production and identification of new, neutron-rich nuclei in the [sup 208]Pb region

The recently developed methods allowing the experimental studies on new neutron-rich nuclei beyond doubly-magic {sup 208}Pb are briefly described. An identification of new neutron-rich isotopes {sup 215}Pb and {sup 217}Bi, and new decay properties of {sup 216}Bi studied by means of a pulsed release element selective technique at PS Booster-ISOLDE are reported.