ISOLDE Research Articles

Laser ion sources for on-line isotope separators

The application of resonant photoionisation using tuneable pulsed laser systems for the production of short-lived radioactive isotopes is discussed. The different ways the laser ionisation is implemented at existing on-line isotope separators is reviewed and the properties, limitations and expectations of the laser ion sources are highlighted.

Selective laser ionization of radioactive Ni-isotopes

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.

High-resolution mass separator and 60 m beam transport line for the radioactive nuclear beam facility at INS

A high-resolution on-line isotope separator (ISOL) followed by a long beam transport line is under testing at INS, as a pilot radioactive beam facility for the E-arena of the Japanese Hadron Project. The ISOL has a unique feature in its high-voltage potential configuration; it has two separation stages and both are electrically insulated from the ground. This feature is effective to eliminate impurities as well as to perform high-resolution mass separation while keeping the injection beam velocity to the post accelerator constant. The design concept and present status of performance tests are reported.

Coupling a total absorption spectrometer to the GSI on-line mass separator

A total absorption spectrometer, constructed and briefly operated at the on-line isotope separator OASIS at Lawrence Berkeley Laboratory, has been moved and installed at the on-line mass separator of GSI Darmstadt. At GSI, the spectrometer has been used for β-decay strength function measurements of nuclei in the vicinity of 100Sn and 146Gd.

Transport efficiency of fission products in IGISOL

Two types of double-room target chambers were constructed for effective stopping of fission fragments in ion-guide isotope separator on-line (IGISOL). It was found that the efficiencies for the double-room chambers are about three and four times larger than that for the standard one. The yield/μC decreases with an increase of the beam intensity. The decreasing trends for both chambers quite resemble each other. This fact suggests that the plasma effect remains even in the double-room chambers. Using the charge distribution of fission products obtained by IGISOL, the yield of RI beam was estimated for the proton-induced fission of 238U.

The TISOL facility at TRIUMF: operational status at 10 years

The TISOL (Test Isotope Separator On-Line) has been in operation for about ten years at the high intensity, intermediate energy proton cyclotron, TRIUMF. On June 12, 1995 funding was announced for the major, new ISOL based accelerated radioactive beams facility, ISAC. The purpose of this report is to review the performance of TISOL and assess its plans for the future.

Holifield Radioactive Ion Beam Facility — status and plans for the near future

The Holifield Radioactive Ion Beam Facility is described. Utilizing the isotope separator on-line technique, this new user facility is coming on-line at the end of 1996. A new experimental endstation centered around the Recoil Mass Spectrometer is also described. Recent data taken on 74Rb and 75Rb is also presented.

High-accuracy mass measurements in ion traps and storage rings

High-accuracy mass measurements have recently been performed on radioactive isotopes produced by proton-induced spallation at the on-line isotope separator ISOLDE at CERN and by heavy-ion projectile fragmentation at the fragment separator FRS at GSI. At ISOLDE, singly charged ions were injected into the Penning trap mass spectrometer ISOLTRAP and their masses determined by observing their cyclotron frequencies in the homogeneous magnetic field of the ion trap. At GSI, bare, hydrogen, or helium-like ions were injected into the experimental storage ring ESR, electron-cooled to the same velocity, and their masses determined by observing their revolution frequencies in the ESR. With ISOLTRAP and ESR, resolving power in the range of 4 × 105< = m/Δ m(FWHM)< = 107 and an accuracy up to \delta m/m~ 10-7 were achieved for radioactive isotopes. Mass measurements of highly charged ions of stable isotopes were performed at Stockholm by use of SMILETRAP. In this case, a resolving power of about 108 and an accuracy close to 10-9 were obtained.

Excited states of154Nd studied through the decay of154Pr

The neutron-rich isotope154Pr, the heaviest isotope of praseodymium, has been investigated byγ-ray multispectrum scaling andγ-γ-(t),X-γ-(t) coincidence experiments. The isotope154Pr was separated from235U fission products with the on-line isotope separator KUR-ISOL. The decay scheme of154Pr has been constructed consisting of 9 excited states and 12 transitions in154Nd, including 7 excited states newly found in the present experiment.

Proposal for a radioactive nuclear beam facility at CIAE

The proposal for a radioactive nuclear beam facility at CIAE is based on the present HI-13 tandem accelerator. A new intensity proton cyclotron accelerator will be built to provide a primary proton beam with 70 MeV, 200 μA. A thick target-ion source system and an on-line isotope mass separator system will produce the interesting exotic radioactive nuclear beam. The beam then passes through a charge exchange canal to change its charge state to negative ion and is injected into the present HI-13 tandem. A super conducting heavy ion linac accelerator will be built as a post accelerator, which can give an energy gain of 17 MeV/ q. A 5 MeV/ A radioactive exotic ion beam with an intensity of more than 6 × 10 8 p.p.s for masses up to A = 130 will be expected with this facility.

The generation of radioactive ion beams

A new design is presented of an ion source of the hollow-cathode type adapted to the on-line isotope separator JASNAPP-2 at JINR, Dubna. To determine its optimal work conditions the source characteristics have been investigated. With the source were generated radioactive fluxes of various isotopes of Po, At, Bi, Pb, Fr and Rn using a 660 MeV proton beam and the Th (p, xpn) reaction. The relative values of the cross-sections for production of the above isotopes are also given.

Targets and ion sources for RIB generation at the Holifield Radioactive Ion Beam Facility

The Holifield Radioactive Ion Beam Facility (HRIBF), now under construction at the Oak Ridge National Laboratory, is based on the use of the well-known on-line isotope separator (ISOL) technique in which radioactive nuclei are produced by fusion type reactions in selectively chosen target materials by high-energy proton, deuteron, or He ion beams from the Oak Ridge Isochronous Cyclotron (ORIC). Among several major challenges posed by generating and accelerating adequate intensities of radioactive ion beams (RIBs), selection of the most appropriate target material for production of the species of interest is, perhaps, the most difficult. In this report, we briefly review present efforts to select target materials and to design composite target matrix/heat-sink systems that simultaneously incorporate the short diffusion lengths, high permeabilities, and controllable temperatures required to effect maximum diffusion release rates of the short-lived species that can be realized at the temperature limits of specific target materials. We also describe the performance characteristics for a selected number of target ion sources that will be employed for initial use at the HRIBF as well as prototype ion sources that show promise for future use for RIB applications.

Identification of a New Isotope166Tb

A new neutron-rich isotope 166 Tb produced in 16 MeV proton-induced fission of 238 U has been identified using the JAERI on-line isotope separator (JAERI-ISOL) coupled to a gas-jet transport system. Dy KX-rays and γ rays originating from the decay of 166 Tb were found in both mass-166 and 182 fractions, where the 166 Tb nuclides were mass-separated as elemental ions 166 Tb + and monoxide ions 166 TbO + , respectively. The half-life of 166 Tb has been determined as 21±6 s, which is much shorter than theoretical predictions. A decay scheme of 166 Tb has been proposed and a probable spin assignment for the 166 Tb ground state has been discussed.

Excited states of 154Nd studied through the decay of 154Pr

The neutron-rich isotope 154Pr, the heaviest isotope of praseodymium, has been investigated by γ-ray multispectrum scaling and γ-γ-(t), X-γ-(t) coincidence experiments. The isotope 154Pr was separated from 235U fission products with the on-line isotope separator KUR-ISOL. The decay scheme of 154Pr has been constructed consisting of 9 excited states and 12 transitions in 154Nd, including 7 excited states newly found in the present experiment.

Ion sources for radioactive beams and related problems (Review) (invited)

Ion sources for radioactive beam facilities are integrated systems of production target and ionizer which have to convert the limited number of particles produced in nuclear reactions efficiently and selectively into an ion beam. The figures of merit for such a system are thus its efficiency for a desired isotope and its discrimination against the unwanted elements. The efficiency is the product of release efficiency (a characteristic of the integrated system) and ionization efficiency, the latter characterizing the ionizing mechanism. The ionizers described include both the ones routinely used in isotope separation on-line as well as promising new developments; they are classified according to their ionizing medium, utilizing electrons, heat, or photons, respectively.

Laser ion source for the Leuven Isotope Separator On-Line

An on-line laser ion source has been developed and coupled to an on-line isotope separator for the production of isotopically and isobarically pure beams of radioactive ions. It is based on element-selective resonant laser ionization of nuclear reaction products thermalized and neutralized in a high-pressure noble gas after their recoil out of the target. Pure beams of 54,55Ni and 54Co, produced in a light-ion-induced fusion-evaporation reaction, and of 113Rh, produced in a proton-induced fission of 238U, were obtained. A preliminary efficiency of the ion source of ∼6% for fusion reactions and of ∼0.2% for fission reactions has been obtained. A selectivity of the ion source of 300 for fusion and 50 for fission reactions limited by the evacuation of non-neutralized reaction products has been achieved.

Status report on the electron cyclotron resonance ion sources used for the production of radioactive ion beams at Louvain-la-Neuve

Two single-stage, 6 GHz electron cyclotron resonance (ECR) ion sources are currently in use at the ARENAS project at Louvain-la-Neuve. One of them is used to ionize radioactive elements to low charge states (1+ to 4+) before injection in the postaccelerator cyclotron. High intensity beams of 6He, 11C, 13N, 18Ne, and 19Ne are being produced. Recently the source has been adapted for the ionization of 18F and the first experiment with this beam has been performed. A second ECR source, almost identical to the first, is used in combination with the Leuven isotope separator on-line. It produces stable and radioactive beams at 50*q keV. Mass separated beams of 13N, 14O, and 15O can be produced using a high-temperature carbon target. An upgrade of this type of ECR source is now under construction. It consists mainly of increased magnetic fields and the capability for insertion of a heated cavity.

Beta + decay of 15.2-min 114Te.

The ${\mathrm{\ensuremath{\beta}}}^{+}$ decay of 15.2 min $^{114}\mathrm{Te}$ into levels of $^{114}\mathrm{Sb}$ was studied through \ensuremath{\gamma}-ray and conversion electron spectroscopy at the UNISOR on-line isotope mass separator. Multiscaled \ensuremath{\gamma}-ray and electron singles provided for the determination of energies and intensities for 94 transitions (68 new) and of internal conversion coefficients for 12 of these transitions. The level scheme was deduced from \ensuremath{\gamma}-\ensuremath{\gamma} and \ensuremath{\gamma}-e coincidence measurements and extended to 2.1 MeV. The energy spectrum and electromagnetic properties of levels and associated transitions were calculated in the interacting boson-fermion-fermion model (IBFFM), with good agreement between experimental and theoretical results. \textcopyright{} 1996 The American Physical Society.

127Ce levels populated in the 4.2 s127Pr beta-decay

From new measurements, a half-live of 4.2±0.3 s has been clearly established in127Pr. This value confirms our first result [4] and rules out other data [5]. The127Pr activity was produced by bombarding92Mo or94Mo targets with 210 MeV40Ca beams. The mass identification has been made using an ion-guide coupled with an on-line isotope separator. The partial level scheme proposed for127Ce has been deduced from β-gated γ spectra and Xγ- and γγ-coincidences. A new band structure based on a 1/2+ state is established.

Recent experiments with radioactive ion beams at GSI

Abstract A review is given over recent experiments performed by means of A·keV to A·GeV radioactive ion beams at GSI Darmstadt. Nuclear structure information on exotic nuclei is discussed as obtained by using an online isotope separator, a velocity filter or a magnetic beam-line spectrometer.