ISOLDE Research Articles

Development and applications of the IGISOL technique

The development and present status of the Ion Guide Isotope Separator On-Line technique is presented. Applications to nuclear physics research include decay spectroscopy of proton- and neutron-rich nuclei of refractory elements and studies of their ground-state properties by collinear laser spectroscopy. Future developments, including ion-beam manipulations by linear RFQ and Penning traps, are discussed together with high-energy applications of the IGISOL technique.

How to produce intense and pure ISOL beams

The three key requirements for all individual parts of an ISOL (Isotope Separation On-Line) facility are efficiency, rapidity and selectivity.

Yields of products from fast neutron-induced fission of 233U measured by means of an isotope separator on-line (ISOL) system

A comprehensive study has been carried out of the yield pattern of fission products formed in fast neutron-induced fission of 233U. The isotope separator on-line facility at Studsvik to the R2-0 nuclear reactor was used for rapid separation of the fission products. At a target temperature of 2250°C fission products of the elements from zinc (Z = 30) to barium (Z = 56) are released, with the exception of yttrium, zirconium, niobium, molybdenum, technetium, ruthenium and rhodium. The individual isotopes are then available for study, implying that an almost complete mapping of the yield distribution can be made. In the analysis, the delay between production and measurement and the overall separator efficiency for three consecutive elements (the one under study and its parent and grand parent) are taken into account. Independent and/or cumulative yields have been obtained for 203 nuclear species, among them 59 isomeric states.

Isomer separation of [formula omitted]Cu and [formula omitted]Cu with a resonance ionization laser ion source

Radioactive copper isotopes were ionized with the resonance ionization laser ion source (RILIS) at the on-line isotope separator ISOLDE (CERN). Using the different hyperfine structure in the 3d 10 4s 2 S 1/2 – 3d 10 4p 2 P 0 1/2 transition the low- and high-spin isomers of 70 Cu were selectively enhanced by tuning the laser wavelength. The light was provided by a narrow-bandwidth dye laser pumped by copper vapor lasers (CVL) and frequency doubled in a BBO crystal. The ground state to isomeric state intensity ratio could be varied by a factor of 30, allowing to assign gamma transitions unambiguously to the decay of the individual isomers. It is shown that the method can also be used to determine magnetic moments. In a first experiment for the 1 + ground state of 70 Cu a magnetic moment of (+)1.8(3) μ N and for the high-spin isomer of 70 Cu a magnetic moment of (±)1.2(3) μ N could be deduced.

Band structure of 146Ce studied through γ-γ angular correlation measurements

The β-decay of 146La was studied using the on-line isotope separator KUR-ISOL. Gamma-gamma angular correlation measurements were performed with a 4-Ge detectors system. Spin assignments of three levels were made: 3+ for the 1576.5 keV level, 4+ for the 1627.1 keV level and 5+ for the 1810.2 keV level. The mixing ratios (E2/M1) were deduced to be δ183.2= 0.25 ± 0.08, δ638.9= 0.33 ± 0.05, δ959.0= 1.19+0.16 −0.14, δ1015.9= 5.4+3.1 −1.5 and δ1318.1= 6.5+1.7 −1.1. These were compared to the calculated values obtained in three cases involving different Majorana force parameter values. The band structure of 146Ce is discussed based on the results of calculation using the IBM-2 theory.

Ion source development for isotope separator on-line based radioactive nuclear beam facility at KEK-Tanashi

For an isotope separator on-line based radioactive nuclear beam facility at KEK-Tanashi, two different types of ion sources are currently employed: a single stage 6.4 GHz electron cyclotron resonance ion source for Ne2+18 and Ne2+19 ions and a surface ionization-type ion source for Li1+8 ions. The production target for Ne radioisotopes is LiF powder. Enclosed in a water-cooled Cu target cell, the target can sustain proton beam power of 120 W for a long term. The methods to suppress unwanted isotopes, like F19 in Ne19 and O18 in Ne18, are discussed. For the production of Li1+8 with the surface ionization-type ion source, a recoil-catcher method is adopted. The feasibility is discussed, comparing to a thick target method.

Accelerated radioactive ion beams: Existing and planned facilities

An over view of existing and planned radioactive ion beam facilities world wide is given. Two types of production methods are distinguished: projectile fragmentation and the on-line isotope separator (ISOL) method. Advanced radioactive beam facilities will allow the production and study of many new nuclei with presently unknown properties.

The ISOLDE facility

The CERN on-line isotope separator facility ISOLDE is a unique tool for studying problems in nuclear, atomic, surface and solid state physics, nuclear medicine and astrophysics. Protons in very short high intensity pulses from the PS Booster are directed on either one of the targets of the two on-line mass separators. The 60 keV ions from them are fed into a common beam transport system to which most of the experiments are connected. The layout of the facility is presented and a detailed description of the two mass separators and the beam distribution system is given. Also the problems of radiation shielding and of the handling of radioactivity are discussed.

Beta-neutrino correlation experiments on laser trapped K-38m, K-37

Laser trapping and cooling techniques are now being applied to the study of nuclear beta-decay at several labs. A magneto-optical trap (MOT) provides a localized source of atoms suspended in space, so the low-energy recoiling nuclei can freely escape and be detected in coincidence with the beta. This allows reconstruction of the neutrino momentum, and the deduction of the beta-nu correlation in a more direct fashion than previously possible. In addition, the nuclei can be polarized by atomic techniques, opening a new class of spin-correlation measurements to test the degree to which parity is maximally violated in the weak interaction. Our present experiment has detected several hundred thousand recoil-beta(+) coincidences from the 0(+) --> 0(+) pure Fermi decay of K-38m, produced at the on-line isotope separators TISOL and ISAC at TRIUMF. Our goal is to set constraints on non-Standard Model scalar bosons competitive with high-energy colliders and more conventional beta-nu correlation experiments.

More than three decades of ISOLDE physics

The ISOLDE on-line isotope separator started its operation in an external beam from the CERN SC in 1967. Since then there has been a steady development of its technical performance and its physics programme so that ISOLDE today is a major facility at CERN.

Isomer separation and measurement of nuclear moments with the ISOLDE RILIS

Short-lived radioisotopes are element selectively ionized by the resonance ionization laser ion source (RILIS) of the on-line isotope separator ISOLDE (CERN). The relative production of low and high spin isomers can be significantly changed when a narrow-bandwidth laser is used to scan through the atomic hyperfine structure. This allows the assignment of gamma ray transitions to the decay of the individual isomers. Moreover, the measurement of the hyperfine splitting provides a very sensitive method for the determination of magnetic moments of exotic isotopes. The technical developments are discussed for the example of copper.

The use of the ion guide technique for collinear laser spectroscopy

The present paper introduces the Ion Guide Isotope Separator On-Line IGISOL. In addition, different ion guide types for different reaction types are reviewed. Further, plans to improve IGISOL performance are presented.

High-efficiency-release targets for use at ISOL facilities: computational design

This report describes efforts made at the Oak Ridge National Laboratory to design high-efficiency-release targets that simultaneously incorporate the short diffusion lengths, high permeabilities, controllable temperatures, and heat-removal properties required for the generation of useful radioactive ion beam (RIB) intensities for nuclear physics and astrophysics research using the isotope separation on-line (ISOL) technique. Short diffusion lengths are achieved either by using thin fibrous target materials or by coating thin layers of selected target material onto low-density carbon fibers such as reticulated-vitreous-carbon fiber (RVCF) or carbon-bonded-carbon fiber (CBCF) to form highly permeable composite target matrices. Computational studies that simulate the generation and removal of primary beam deposited heat from target materials have been conducted to optimize the design of target/heat-sink systems for generating RIBs. The results derived from diffusion release-rate simulation studies for selected targets and thermal analyses of temperature distributions within a prototype target/heat-sink system subjected to primary ion beam irradiation are presented in this report.

Radioactive Nuclear Beams

In his News Focus article (1 Oct., p. [28][1]), Andrew Watson describes the current effort to create facilities that will produce slow nuclear beams by postacceleration of rare isotopes. The article, however, may leave the impression that the other main technique for exploring nuclear structure, based on fast direct beams from heavy-ion fragmentation, will be superseded because of “poor beam intensity.” This is definitely not the case. The greatest scientific perspective in research with radioactive beams lies in the exploration of exotic nuclear species at the limits of stability of the nucleus. Experience from the last couple of years suggests that, for this purpose, the high-energy beams from the fragmentation of heavy ions are superior to beams produced from isotope separation online (ISOL) combined with passage of sorted radioactive nuclei through a small accelerator. As a rough measure, in a study based on nuclear reactions, the same amount of information can be obtained with a fragmentation beam that is a factor of 100,000 weaker than an ISOL beam of the same isotope. Because the production rates are comparable, this implies that direct fragmentation beams will reach several mass numbers farther away from stability, to rare species produced with very small probabilities. This pioneering exploration is already in progress at existing fragment separators at major heavy-ion laboratories: the Large National Accelerator for Heavy Ions (GANIL) in Caen, France; the Center for Heavy-Ion Research (GSI) in Darmstadt, Germany; the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University; and the Institute of Physical and Chemical Research (RIKEN) in Tokyo, Japan. An upgrade now in progress here at the NSCL will by 2001 increase our beam intensity by about a factor of 1000 over the current value. Any plan for the future must have even more powerful fragmentation beams as a major, if not the main, component. For a future heavy-ion machine representing the ultimate in modern technology, the “second-generation” radioactive-beam facility referred to in Watson's article, the fragmentation beams are expected to have at least the same intensity as those based on the ISOL technique. [1]: /lookup/doi/10.1126/science.286.5437.28

A new technique for the production of 17F beams

We have demonstrated that radioactive beams of Al17F+can be produced with intensities as high as 3×108 ions/s using the conventional Isotope Separation On-Line (ISOL) technique employing fibrous HfO2 target material and an external source of Al vapor. Commercially available HfO2 cloth composed of Φ=4–6 μm fibers packed to ∼12% of the bulk density of HfO2, was irradiated with ∼2 μA of 44 MeV deuterons from the Oak Ridge Isochronous Cyclotron (ORIC). The target material (1.6 g/cm2) was contained in a high-temperature reservoir which was coupled through a heated transfer line, to a conventional plasma ion source where the radioactive ion beam was extracted. During irradiation, a flux of elemental Al vapor was directed through the fibrous material forming a transportable molecule which was then extracted from the source as Al17F+. A detailed description of this technique is given and the results of this initial experiment are discussed. The target system was used to inject 17F into the tandem electrostatic accelerator at the Holifield Radioactive Ion Beam Facility (HRIBF) and used to study the 17F(p,p)17F excitation function in the 17F energy range of 10–12 MeV.

Emission channeling studies of defect annealing in the wide band gap semiconductors ZnTe and ZnSe

The Emission Channeling technique has been applied to probe the lattice sites of radioactive 8Li and 111mCd implanted in the wide band gap semiconductors ZnTe and ZnSe, and to study the annealing behaviour of radiation induced lattice damage. The probe ions were implanted at 60 keV energy into single crystal samples at the on-line isotope separator, ISOLDE, at CERN. On implantation at low temperature (⩽180 K) the Li atoms take up tetrahedral interstitial sites in both samples. A site change of the Li atoms from interstitial to substitutional takes place with increasing temperature. In ZnSe the substitutional fraction ( f S ) reaches its maximum value (55%) at 275 K and maintains this value until 510 K; in ZnTe maximum f S (50%) is reached at 250 K and maintained until 440 K. At higher temperatures the Li atoms diffuse to the surface in ZnTe and to extended defects within the crystal in ZnSe. Annealing studies with emission channeling measurements with 111mCd probes show that amorphization and lattice recovery depend strongly on sample and implantation dose.

β-decay half-lives of new neutron-rich isotopes 167,168Tb and levels in 167,168Dy

$\ensuremath{\beta}$-decay half-lives of new neutron-rich isotopes ${}^{167}\mathrm{Tb}$ and ${}^{168}\mathrm{Tb}$ produced in the 20 MeV proton-induced fission of ${}^{238}\mathrm{U}$ have been determined to be 19.4(27) s and 8.2(13) s, respectively, using a gas-jet coupled on-line isotope separator. The present half-lives and those of the recently identified nuclei ${}^{159}\mathrm{Pm},$ ${}^{161}\mathrm{Sm},$ ${}^{165}\mathrm{Gd},$ ${}^{166}\mathrm{Tb}$ were compared with theoretical predictions. The recent calculation by the gross theory with the new one-particle strength functions shows quite good agreement with the experimental half-lives. Excited states of the daughter nuclides ${}^{167}\mathrm{Dy}$ and ${}^{168}\mathrm{Dy}$ have been established for the first time. Level energies of the first ${2}^{+}$ states in even-even Dy isotopes were found to show an irregular behavior at ${}^{164}\mathrm{Dy}$ and increasing deformation toward the neutron midshell around $N\ensuremath{\approx}104$.

High-accuracy mass determination of unstable cesium and barium isotopes

Direct mass measurements of short-lived Cs and Ba isotopes have been performed with the tandem Penning trap mass spectrometer ISOLTRAP installed at the on-line isotope separator ISOLDE at CERN. Typically, a mass resolving power of 600 000 and an accuracy of δm ≈ 13 keV have been obtained. The masses of 123,124,126Ba and 122 m Cs were measured for the first time. A least-squares adjustment has been performed and the experimental masses are compared with theoretical ones, particularly in the frame of a macroscopic-microscopic model.

Studies on the level structure of 152Nd

The structure of 152Nd, produced via β− decay of 152Pr, has been investigated using γ-γ coincidence, γ-γ angular correlation, and β-γ-γ triple coincidence measurements. Praseodymium activities were obtained by the thermal neutron fission of 235U and collected by the on-line isotope separator KUR-ISOL. Nineteen γ-rays and four excited states were newly found. The spins of six exited states were determined and the parities of three of them were also deduced. The spin and parity of the 152Pr ground state, which were previously considered as 4−, are proposed to be 4+ by the present study.

Isomeric yield ratios of fission products in proton-induced fission of232Th

Isomeric yield ratios of 11 fission products were measured in the system of 13 MeV proton-induced fission of232Th by an on-line ion-guide isotope separator. It was found that the closed shell structures of primary fragments and their complementary fragments affect the isomeric yield ratios. Isomeric yield ratios of121Cd (11/2−, 3/2+) and135Xe (11/2−, 3/2+) were measured precisely in the proton energy range of 13 to 26 MeV to investigate their energy dependence. It was found that the isomeric yield ratios increased slightly with proton energy. The results were discussed in connection with the deformation of fission fragments and fission modes.