Isotope Separator On-Line Facility Research Articles

Low-velocity transient-field technique with radioactive ion beams:gfactor of the first excited 2+state in72Zn

The $g$ factor of the first excited ${2}^{+}$ state in ${}^{72}\mathrm{Zn}$ has been measured using the transient-field (TF) technique in combination with Coulomb excitation in inverse kinematics. This experiment presents only the third successful application of the TF method to a short-lived radioactive beam in 10 y, highlighting the intricacies of applying this technique to present and future isotope separator on-line facilities. The significance of the experimental result, $g({2}_{1}^{+})=+0.47(14)$, for establishing the structure of the Zn isotopes near $N=40$ is discussed on the basis of shell-model and beyond-mean-field calculations, the latter accounting for the triaxial degree of freedom, configuration mixing, and particle number and angular momentum projections.

Design study of a re-bunching RFQ for the SPES project

An upgrade to the 2nd generation of the selective production of exotic species (SPES) to produce a radioactive ion beam (RIB) has been studied at the istituto nazionale di fisica nucleare — laboratory nazionali di Legnaro (INFN-LNL). Due to the long distance between the isotope separator online (ISOL) facility and the superconducting quarter wave resonator (QWR) cavity acceleratore lineare per ioni (ALPI), a new re-buncher cavity must be introduced to maintain the high beam quality during the beam transport. A particular radio frequency quadrupole (RFQ) structure has been suggested to meet the requirements of this project. A window-type RFQ, which has a high mode separation, less power dissipation and compact size compared to the conventional normal 4-vane RFQ, has been introduced. The RF design has been studied considering the requirements of the re-bunching machine for high figures of merit such as a proper operation frequency, a high shunt impedance, a high quality factor, a low power dissipation, etc. A sensitivity analysis of the fabrication and the misalignment error has been conducted. A micro-movement slug tuner has been introduced to compensate for the frequency variations that may occur due to the beam loading, the thermal instability, the microphonic effect, etc.

An ion guide laser ion source for isobar-suppressed rare isotope beams

Modern experiments at isotope separator on-line (ISOL) facilities like ISAC at TRIUMF often depend critically on the purity of the delivered rare isotope beams. Therefore, highly selective ion sources are essential. This article presents the development and successful on-line operation of an ion guide laser ion source (IG-LIS) for the production of ion beams free of isobaric contamination. Thermionic ions from the hot ISOL target are suppressed by an electrostatic potential barrier, while neutral radio nuclides effusing out are resonantly ionized by laser radiation within a quadrupole ion guide behind this barrier. The IG-LIS was developed through detailed thermal and ion optics simulation studies and off-line tests with stable isotopes. In a first on-line run with a SiC target a suppression of surface-ionized Na contaminants in the ion beam of up to six orders of magnitude was demonstrated.

Resonance ionization laser ion sources for on-line isotope separators (invited)

A Resonance Ionization Laser Ion Source (RILIS) is today considered an essential component of the majority of Isotope Separator On Line (ISOL) facilities; there are seven laser ion sources currently operational at ISOL facilities worldwide and several more are under development. The ionization mechanism is a highly element selective multi-step resonance photo-absorption process that requires a specifically tailored laser configuration for each chemical element. For some isotopes, isomer selective ionization may even be achieved by exploiting the differences in hyperfine structures of an atomic transition for different nuclear spin states. For many radioactive ion beam experiments, laser resonance ionization is the only means of achieving an acceptable level of beam purity without compromising isotope yield. Furthermore, by performing element selection at the location of the ion source, the propagation of unwanted radioactivity downstream of the target assembly is reduced. Whilst advances in laser technology have improved the performance and reliability of laser ion sources and broadened the range of suitable commercially available laser systems, many recent developments have focused rather on the laser/atom interaction region in the quest for increased selectivity and/or improved spectral resolution. Much of the progress in this area has been achieved by decoupling the laser ionization from competing ionization processes through the use of a laser/atom interaction region that is physically separated from the target chamber. A new application of gas catcher laser ion source technology promises to expand the capabilities of projectile fragmentation facilities through the conversion of otherwise discarded reaction fragments into high-purity low-energy ion beams. A summary of recent RILIS developments and the current status of laser ion sources worldwide is presented.

Nuclear-physics applications of MYRRHA

The Belgian Nuclear Research Centre SCKCEN is currently working on the design of the MYRRHA research reactor, able to operate in both critical and sub-critical mode as an Accelerator-Driven System (ADS). When operated as an ADS, the MYRRHA reactor core will be coupled to an external neutron source, which is generated by a 600- MeV, 2- to 4-mA proton beam impinging on a lead-bismuth spallation target. By using a small fraction (up to 5%) of the MYRRHA proton beam, intensities of 100-200 A can be sent to a separate facility called ISOL@MYRRHA. Given the high proton energy, most isotopes known on the chart of nuclides can be produced. The production in the hot-target is followed by selective ionization and extraction of atoms in a Radioactive Ion Beam (RIB). Following mass-purification, high-intensity RIBs will be delivered for a large variety of experimental programmes requiring long measurement times. By its experimental programme, the ISOL@MYRRHA facility will be complementary to running and planned Isotope Separator On-Line (ISOL) facilities in Europe and abroad.

Design study of 10 kW direct fission target for RISP project

We are developing Isotope Separation On-Line (ISOL) target system, which consists of 1.3 mm-thick uranium-carbide multi-disks and cylindrical tantalum heater, to be installed in new facility for Rare Isotope Science Project in Korea. The intense neutron-rich nuclei are produced via the fission process using the uranium carbide targets with a 70 MeV proton beam. The fission rate was estimated to be 1.5 10 13 /sec for 10 kW proton beam. The target system has been designed to be operated at a temperature of 2000 C so as to improve the release e ciency. Production and delivery of high purity intense of Rare Isotope Beam (RIB) have been a major con- cern for fundamental research fields such as astro and nuclear physics as well as applied research field such as material and bio-medical science. Rare Isotope Science Project (RISP) of Korea has proposed to construct Isotope Separation On-Line (ISOL) facility in order to provide the intense rare isotopes. The ISOL target enables us not only to produce the nuclei with the medium mass neutron- rich region but also to obtain their high production rates. A uniform 70 MeV proton beam with a maximum current of 500 A, which is delivered from a cyclotron driver, will impinge on an uranium carbide target. The neutron-rich isotopes are produced via proton-induced fission. A singly charged (1+) RIB is produced and extracted from the target and the ion source, respectively, then the beam emittance is reduced by a RF-cooler to be 3 mm mrad before injecting to the high resolution mass separator (HRMS). The isotopes selected by the HRMS are delivered to an electron beam ion source (EBIS) or an electron cyclotron resonance (ECR) type charge breeder so as to breed the charge from the 1 + charge state to a n + charge state for e cient and economical post-acceleration. An A=q sepa- rator is installed at the downstream of the charge breeder to purify the ion beam contaminated during charge breeding. Here, we report on the results of the ISOL target design for 10 kW proton beam. The main issues concerning the design of the ISOL target can be divided into three categories; in- target fission rate, release time, and temperature of the target. Firstly, a total e ective thickness of the target should be as thick as possible in order to maximize the in-target fission rate. This requires a large size of the target. Secondly, release time should be as short as possible so as to minimize the losses by the decay of isotopes. A small size of the target helps to reduce the release time by decreasing the flight length of the isotopes. However, it should be noted here that the small size can lead to melt down of the target due to the reduced radiant cooling. Lastly, the temperature of the target should be as high as possible to increase the thermal velocity of the isotopes, which leads to the reduction of the release time. Therefore, the correlations between the three points mentioned above should be investigated so as to find the optimum condition for the ISOL target.

Two-step laser ionization schemes for in-gas laser ionization and spectroscopy of radioactive isotopes

The in-gas laser ionization and spectroscopy technique has been developed at the Leuven isotope separator on-line facility for the production and in-source laser spectroscopy studies of short-lived radioactive isotopes. In this article, results from a study to identify efficient optical schemes for the two-step resonance laser ionization of 18 elements are presented.

ISOL facility for rare isotope beams at RAON

The Rare Isotope Science Project (RISP) in Korea is developing the Rare Isotope (RI) Accelerator, RAON. The RAON is planned to be an advanced RI beam using isotope separation on-line (ISOL) with a high-power target. The main goal of the ISOL facility is to deliver high-quality, intense, neutron-rich (n-rich) beams to the experimental hall; for example 108 atoms per second of the 132Sn n-rich reference isotope. The RAON ISOL facility consists of mainly two systems. One is the RI production system of a high-power uranium fission target combined with the Forced Electron Beam Induced Arc Discharge (FEBIAD) ion source, Surface Ionization (SI) ion source and Resonance Ionization Laser Ion Source (RILIS), in which system the final goal for the RI production rate is 1014 fission per second. The other is the RI beam purification system, which is comprised of an RF beam cooler, a high resolution mass separator (HRMS), a charge breeder and a charge state separator, and the design goal is to deliver the RI beam with a mass resolving power up to 45,000 and with a limit of 6 × 105 background counts per second. The current status of the ISOL facility of the RISP is reported.

Ionization efficiency estimations for the SPES surface ion source

Ion sources play a crucial role in ISOL (Isotope Separation On Line) facilities determining, with the target production system, the ion beam types available for experiments. In the framework of the SPES (Selective Production of Exotic Species) INFN (Istituto Nazionale di Fisica Nucleare) project, a preliminary study of the alkali metal isotopes ionization process was performed, by means of a surface ion source prototype. In particular, taking into consideration the specific SPES in-target isotope production, Cs and Rb ion beams were produced, using a dedicated test bench at LNL (Laboratori Nazionali di Legnaro). In this work the ionization efficiency test results for the SPES Ta surface ion source prototype are presented and discussed.

Recommissioning of JYFLTRAP at the new IGISOL-4 facility

The JYFLTRAP double Penning-trap system was moved to a new location along with the Ion Guide Isotope Separator On-line (IGISOL) facility at the Accelerator Laboratory of the University of Jyväskylä. The move made it possible to upgrade various parts of the facility. For example, separate beam lines for JYFLTRAP and the collinear laser spectroscopy station were constructed after the radio-frequency quadrupole cooler and buncher. In this contribution we give an overview of the new JYFLTRAP facility and results from the first stable ion-beam tests.

Towards commissioning the new IGISOL-4 facility

The Ion Guide Isotope Separator On-Line facility at the Accelerator Laboratory of the University of Jyväskylä is currently being re-commissioned as IGISOL-4 in a new experimental hall. Access to intense beams of protons and deuterons from a new MCC30/15 cyclotron, with continued possibility to deliver heavy-ion beams from the K=130MeV cyclotron, offers extensive opportunities for long periods of fundamental experimental research, developments and applications. A new layout of beam lines with a considerable increase in floor space offers new modes of operation at the facility, as well as a possibility to incorporate more complex detector setups. We present a general overview of IGISOL-4 and the current status of several projects, including the collinear laser spectroscopy station and the future of neutron-induced fission. Recent milestones from the first commissioning experiments are presented.

An IGISOL portrait

This issue of Hyperfine Interactions consists of 21 articles describing scientific work related to the research at the on-line isotope separator facility IGISOL at the University of Jyvaskyla, Finland. Ten contributions containing a significant amount of original results, earlier unpublished, have been presented as a Topical Collection in the European Physical Journal (EPJA 48 issue No 4, 2012). In the early 1980s, the Ion Guide Isotope Separator On-Line (IGISOL) concept was realized at the 20 MeV proton cyclotron of the Physics Department at the University of Jyvaskyla (JYFL). For the first time, the technique allowed the production of high quality ISOL beams from nuclear reaction products with millisecond delay times without chemical restrictions. By providing access to short-lived isotopes of refractory elements it opened up new regions in the nuclear chart for nuclear decayand ground-state spectroscopy. During the 1980s, the main research activity at IGISOL was decay spectroscopy, and in particular, of fission products produced in proton-induced fission of natural uranium. Approximately 40 new isotopes and isomers were discovered and studied employing beta-, gamma-, and conversion electron spectroscopy. These experiments covered a broad range of neutron-rich nuclei from yttrium (Z = 39) to cadmium (Z = 48) and revealed how their structure was developing between highly deformed zirconium through triaxial ruthenium isotopes to weakly deformed vibrational cadmium isotopes. The original IGISOL facility was shut down in October 1991 and was reinstalled as IGISOL-2 at the science campus housing the laboratory for the K = 130 MeV heavy ion cyclotron. A new window of opportunity for extending research to neutrondeficient nuclei far from stability was opened and was going to have a strong impact

Neutron-rich isotope production using a uranium carbide - carbon nanotubes SPES target prototype

The SPES (Selective Production of Exotic Species) project, under development at the Istituto Nazionale di Fisica Nucleare - Laboratori Nazionali di Legnaro (INFN-LNL), is a new-generation Isotope Separation On-Line (ISOL) facility for the production of radioactive ion beams by means of the proton-induced fission of uranium. In the framework of the research on the SPES target, seven uranium carbide discs, obtained by reacting uranium oxide with graphite and carbon nanotubes, were irradiated with protons at the Holifield Radioactive Ion Beam Facility (HRIBF) of Oak Ridge National Laboratory (ORNL). In the following, the yields of several fission products obtained during the experiment are presented and discussed. The experimental results are then compared to those obtained using a standard uranium carbide target. The reported data highlights the capability of the new type of SPES target to produce and release isotopes of interest for the nuclear physics community.

The Miniball spectrometer

The Miniball germanium detector array has been operational at the REX (Radioactive ion beam EXperiment) post accelerator at the Isotope Separator On-Line facility ISOLDE at CERN since 2001. During the last decade, a series of successful Coulomb excitation and transfer reaction studies have been performed with this array, utilizing the unique and high-quality radioactive ion beams which are available at ISOLDE. In this article, an overview is given of the technical details of the full Miniball setup, including a description of the \(\gamma\)-ray and particle detectors, beam monitoring devices and methods to deal with beam contamination. The specific timing properties of the REX-ISOLDE facility are highlighted to indicate the sensitivity that can be achieved with the full Miniball setup. The article is finalized with a summary of some physics highlights at REX-ISOLDE and the utilization of the Miniball germanium detectors at other facilities.

First on-line results from the CRIS (Collinear Resonant Ionisation Spectroscopy) beam line at ISOLDE

The CRIS (Collinear Resonant Ionisation Spectroscopy) experiment at the on-line isotope separator facility, ISOLDE, CERN, has been constructed for high-sensitivity laser spectroscopy measurements on radioactive isotopes. The technique determines the magnetic dipole and electric quadrupole moments, nuclear spin and changes in mean-square charge radii of exotic nuclei via measurement of their hyperfine structures and isotope shifts. In November 2011 the first on-line run was performed using the CRIS beam line, when the hyperfine structure of 207Fr was successfully measured. This paper will describe the technique and experimental setup of CRIS and present the results from the first on-line experiment.

Optimization studies of the CERN-ISOLDE neutron converter and fission target system

The ISOLDE facility at CERN has been one of the leading isotope separator on-line (ISOL) facilities worldwide since it became operative in 1967. More than 1000 isotopes are available at ISOLDE, produced after the bombardment of various primary targets with a pulsed proton beam of energy 1.4 GeV and an average intensity of 2 μA. A tungsten solid neutron converter has been used for ten years to produce neutron-rich fission fragments in UCx targets. In this work, the Monte Carlo code FLUKA and the cross-section codes TALYS and ABRABLA were used to study the current layout of the neutron converter and fission target system of the ISOLDE facility. An optimized target system layout is proposed, which maximizes the production of neutron-rich isotopes and reduces the contamination by undesired neutron-deficient isobars. The studies here reported can already be applied to ISOLDE and will be of special relevance for the future facilities HIE-ISOLDE and EURISOL.

Overview of the KoRIA Facility for Rare Isotope Beams

The Korea Rare Isotope Accelerator, currently referred to as KoRIA, is briefly presented. The KoRIA facility is aimed to enable cutting-edge sciences in a wide range of fields. It consists of a 70 kW isotope separator on-line (ISOL) facility driven by a 70 MeV, 1 mA proton cyclotron and a 400 kW in-flight fragmentation (IFF) facility. The ISOL facility uses a superconducting (SC) linac for post-acceleration of rare isotopes up to about 18 MeV/u, while the SC linac of IFF facility is capable of accelerating uranium beams up to 200 MeV/u, 8 pμA and proton beams up to 600 MeV, 660 μA. Overall features of the KoRIA facility are presented with a focus on the accelerator design.

Decays of T Z = − 3/2 nuclei 23Al, 31Cl, and 41Ti

This article gives an overview on the decay spectroscopy of T Z = –3/2 nuclei 23Al, 31Cl, and 41Ti performed at the Ion Guide Isotope Separator On-Line (IGISOL) facility. The results of the IGISOL experiments are compared to the experimental results that have been published since. The isobaric multiplet mass equation (IMME) has been studied for the T = 3/2 quartets at A = 23 and A = 31. For 41Ti, a detailed comparison to the Gamow–Teller strengths obtained for the analog transitions via charge-exchange reactions has been done. Further improvements in the experimental instrumentation and methods and possible implementations for studying T Z = –3/2 nuclei at the new IGISOL facility are discussed.

Isomer and decay studies for the rp process at IGISOL

This article reviews the decay studies of neutron-deficient nuclei within the mass region \(\ensuremath A=56\mbox{--}100\) performed at the Ion-Guide Isotope Separator On-Line (IGISOL) facility in the University of Jyväskylä over last 25 years. Development from He-jet measurements to on-line mass spectrometry, and eventually to atomic mass measurements and post-trap spectroscopy at IGISOL, has yielded studies of around 100 neutron-deficient nuclei over the years. The studies form a solid foundation to astrophysical rp -process path modelling. The focus is on isomers studied either via spectroscopy or via Penning-trap mass measurements. The review is complemented with recent results on the ground and isomeric states of 90Tc . The excitation energy of the low-spin isomer in 90Tc has been measured as \(\ensuremath E_x=144.1(17)\) keV with JYFLTRAP double Penning trap and the ground state of 90Tc has been confirmed to be the (8+) state with a half-life of \(\ensuremath T_{1/2}=49.2(4)\) s. Finally, the mass-excess results for the spin-gap isomers 53Com and 95Pdm and implications from the JYFLTRAP mass measurements for the (21+) isomer in 94Ag are discussed.

Initial commissioning results with the NSCL Electron Beam Ion Trap

The ReA reaccelerator is being added to the National Superconducting Cyclotron Laboratory (NSCL) fragmentation facility in order to provide exotic rare-isotope beams, not available at the Isotope Separation On-Line facilities, in the several-MeV/u energy range. The first stage of the NSCL reaccelerator complex, consisting of an EBIT charge breeder, a room-temperature radiofrequency quadrupole (RFQ) accelerator, and superconducting linear accelerator modules, has been completed and is being put into operation. Commissioning of the EBIT has started by extracting charge-bred residual gas ions, ions created from a Ne gas jet directed across the EBIT's electron beam and ions captured from an external test ion source. Charge-bred ions from the Ne gas jet have been extracted as a pulse and accelerated through the RFQ and the two cryomodules.