ISOLDE Research Articles

Masses of neutron-rich Ni and Cu isotopes and the shell closure at Z = 28 , N = 40

The Penning trap mass spectrometer JYFLTRAP, coupled to the Ion Guide Isotope Separator On-Line (IGISOL) facility at Jyvaskyla, was employed to measure the atomic masses of neutron-rich 70-73Ni and 73, 75Cu isotopes with a typical accuracy less than 5keV. The mass of 73Ni was measured for the first time. Comparisons with the previous data are discussed. Two-neutron separation energies show a weak subshell closure at 68 28Ni40 . A well established proton shell gap is observed at Z = 28 .

Splitting of high power, cw proton beams

A simple method for splitting a high power, continuous wave (cw) proton beam in two or more branches with low losses has been developed in the framework of the EURISOL (European Isotope Separation On-Line Radioactive Ion Beam Facility) design study. The aim of the system is to deliver up to 4 MW of ${\mathrm{H}}^{\ensuremath{-}}$ beam to the main radioactive ion beam production target, and up to 100 kW of proton beams to three more targets, simultaneously. A three-step method is used, which includes magnetic neutralization of a fraction of the main ${\mathrm{H}}^{\ensuremath{-}}$ beam, magnetic splitting of ${\mathrm{H}}^{\ensuremath{-}}$ and ${\mathrm{H}}^{0}$, and stripping of ${\mathrm{H}}^{0}$ to ${\mathrm{H}}^{+}$. The method allows slow raising and individual fine adjustment of the beam intensity in each branch.

Confirmation of parity violation in the γ decay of180Hfm

This paper reports measurements made using the technique of online nuclear orientation which reexamine the \ensuremath{\gamma} decay of isomeric ${}^{180}{\mathrm{Hf}}^{\mathrm{m}}$ and specifically the 501 keV ${8}^{\ensuremath{-}}$--${6}^{+}$ transition. The irregular admixture of $E2$ to $M2/E3$ multipolarity in this transition, deduced from the forward-backward asymmetry of its angular distribution, has for decades stood as the prime evidence for parity mixing in nuclear states. The experiment, based on ion implantation of the newly developed mass-separated ${}^{180}{\mathrm{Hf}}^{\mathrm{m}}$ beam at the CERN online isotope mass separator (ISOLDE) facility into an iron foil maintained at millikelvin temperatures, produces higher degrees of polarization than were achieved in previous studies of this system. The value found for the $E2/M2$ mixing ratio, $\ensuremath{\epsilon}=\ensuremath{-}0.0324$(16)(19), is in close agreement with the previous published average value $\ensuremath{\epsilon}=\ensuremath{-}0.030$(2), in full confirmation of the presence of the irregular $E2$ admixture in the 501 keV transition. The temperature dependence of the forward-backward asymmetry has been measured over a more extended range of nuclear polarization than previously possible, giving further evidence for parity mixing of the ${8}^{\ensuremath{-}}$ and ${8}^{+}$ levels and the deduced $E2/M2$ mixing ratio.

Status of JAEA–KEK radioactive ion beam facility, TRIAC

In collaboration with Japan Atomic Energy Agency (JAEA) and High Energy Accelerator Research Organization (KEK), we have been constructed an ISOL-based radioactive ion beam facility, Tokai Radioactive Ion Accelerator Complex (TRIAC), at JAEA – Tokai. This facility consists of a Charge-Breeding 18GHz Electron Cyclotron Resonance Ion-Source (CB-ECRIS), the Split-Coaxial Radio-Frequency Quadrupole (SCRFQ)- and Interdigital-H (IH)-type linacs. An Isotope Separator On-line (JAEA–ISOL) is connected to the CB-ECRIS as the injector of radioactive ions which are produced in proton-induced fission of uranium and heavy-ion reaction. The primary beams are provided from the JAEA Tandem Accelerator. Radioactive singly-charged ions from the JAEA–ISOL are bred to q/A⩾1/7 in the CB-ECRIS and then multi-charged ions are accelerated with the linac-complex from 2keV/u to the energy between 0.14 and 1.1MeV/u. So far, we successfully accelerate 8Li+ and 138Xe20+, the acceleration energy of 1.1MeV/u was achieved. From October 2005, some radioactive ion beams of 1.1MeV/u have become available for users.

Precise atomic masses of neutron-rich Br and Rb nuclei close to the r-process path

The Penning trap mass spectrometer JYFLTRAP, coupled to the Ion-Guide Isotope Separator On-Line (IGISOL) facility at Jyvaskyla, was employed to measure the atomic masses of neutron rich 85 to 92Br and 94 to 97Rb isotopes with a typical accuracy less than 10 keV. Discrepancies with the older data are discussed. Comparison to different mass models is presented. Details of nuclear structure, shell and subshell closures are investigated by studying the two-neutron separation energy and the shell gap energy.

Development of the RF-IGISOL at CYRIC

An rf ion guide for mass separation of fission fragments has been developed as a new type of the ion-source of an ion guide isotope separator on-line (IGISOL). Fission fragments from an uranium target are thermalized in a large helium gas cell and extracted by a combination of dc and inhomogeneous rf electric fields. They are subsequently mass separated by an electromagnetic mass separator. Test experiments with a radioactive α-source and with fission fragments produced in the proton-induced fission of 238U reveal that the yields of mass-separated radioactive ion beams are enhanced, due to the dc and rf electric fields in the gas cell.

Development of a RILIS ionisation scheme for gold at ISOLDE, CERN

At the ISOLDE on-line isotope separation facility, the resonance ionisation laser ion source (RILIS) can be used to ionise reaction products as they effuse from the target. The RILIS process of laser step-wise resonance ionisation of atoms in a hot metal cavity provides a highly element selective stage in the preparation of the radioactive ion beam. As a result, the ISOLDE mass separators can provide beams of a chosen isotope with greatly reduced isobaric contamination. With the addition of a new three-step ionisation scheme for gold, the RILIS is now capable of ionising 26 of the elements. The optimal scheme was determined during an extensive study of the atomic energy levels and auto-ionising states of gold, carried out by means of in-source resonance ionisation spectroscopy. Details of the ionisation scheme and a summary of the spectroscopy study are presented.

α decay ofCm238and the new isotopeCm237

Alpha decays of $^{237}\mathrm{Cm}$ and $^{238}\mathrm{Cm}$ have been studied using a gas-jet coupled on-line isotope separator. The new isotope $^{237}\mathrm{Cm}$ has been identified through the detection of $6656\ifmmode\pm\else\textpm\fi{}10$ keV \ensuremath{\alpha} particles. The \ensuremath{\alpha} energy of $^{238}\mathrm{Cm}$ has been revised more precisely than the previous one. The \ensuremath{\alpha} transition to the first excited ${2}^{+}$ state in $^{234}\mathrm{Pu}$ has also been observed. It was found that the ${2}^{+}$ energy in $^{234}\mathrm{Pu}$ is much higher than those in heavier Pu isotopes.

Rare Isotope Accelerator (RIA) Project

The proposed Rare Isotope Accelerator (RIA) Project will provide world-class intensities of radioactive beams created by any of the known production mechanisms. A driver linac will be used to accelerate any stable isotope from protons through uranium to energies of ⩾400 MeV/u and intensities of ⩾100 kW. Lighter elements will be used to produce radioactive ion beams by the isotope separation on line (ISOL) method. Typically heavier elements will be used to produce radioactive ion beams by the particle fragmentation (PF) method. A hybrid method of stopping radioactive ion beams produced by the PF method in a gas cell will also be employed. The RIA project has strong support from the nuclear science community as evidenced by RIA being the highest priority for major new construction in the most recent Nuclear Science Advisory Committee (NSAC) Long Range Plan [2002 NSAC Long-Range Plan: Opportunities in Nuclear Science, A long-range plan for the next decade, April 2002]. In addition, RIA is tied for third position for the near term priorities of the Department of Energy (DoE) 20-year plan [DOE Office of Science, Facilities for the future of science: a twenty-year outlook. http://www.sc.doe.gov/Sub/Facilities_for_future/facilities_future.htm]. The status of the RIA design is presented.

Experimental apparatus at KUR-ISOL to identify isomeric transitions from fission products, and decay spectroscopy of 151Ce

Decay studies on 151Ce have been performed using the on-line isotope separator connected to the Kyoto University Reactor. In addition to conventional γ and conversion electron spectroscopy, β -gated measurements were carried out on mass-separated 151Ce to identify an isomeric transition. From the analysis of the obtained data, the half-life of the isotope was ascertained to be 1.76(6) s and a decay scheme containing six excited levels was constructed for the first time. The excited level at 35.1 keV in 151Pr was found to be a long-lived state (a half-life of approximately 10 μ s or longer).

Production of intense radioactive beams at ISAC using low-energy protons

A proof-of-principle approach for the production of intense (~108/s) radioactive ion beams, which differs from the standard ISOL (Isotope Separation On-Line) technique, has been demonstrated successfully using 11C at the TRIUMF laboratory. This approach uses 13 MeV protons produced by a medical cyclotron and should be useful for a range of radioisotopes of interest to the nuclear astrophysics research programme.PACS No.: 29.25.Rm

Ionization Scheme Development at the ISOLDE RILIS

The resonance ionization laser ion source (RILIS) of the ISOLDE on-line isotope separation facility is based on the method of laser step-wise resonance ionization of atoms in a hot metal cavity. The atomic selectivity of the RILIS complements 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 vapour lasers, ion beams of 24 elements have been generated at ISOLDE with ionization efficiencies in the range of 0.5-15%. As part of the ongoing RILIS development off-line resonance ionization spectroscopy studies carried out in 2003 and 2004 have determined the optimal three-step ionization schemes for scandium, antimony, dysprosium and yttrium.

Particle and radiation simulations for the proposed rare isotope accelerator facility

The Rare Isotope Accelerator (RIA) facility, planned to be built in the USA, will be capable of delivering diverse beams, from protons to uranium ions, with energies from 1 GeV to at least 400 MeV per nucleon to rare isotope-producing targets. High beam power—400 kW—will allow RIA to become the most powerful rare isotope beam facility in the world; however, it also creates challenges for the design of the isotope-production targets. This paper focuses on the isotope-separator-on-line (ISOL) target work, particularly the radiation transport aspects of the two-step fission target design. Simulations were performed with the PHITS, MCNPX, and MARS15 computer codes. A two-step ISOL target considered here consists of a mercury or tungsten primary target in which primary beam interactions release neutrons, which in turn induce fissions—and produce rare isotopes—in the secondary target filled with fissionable material. Three primary beams were considered: 1-GeV protons, 622-MeV/u deuterons, and 777-MeV/u 3He ions. The proton and deuterium beams were found to be about equivalent in terms of induced fission rates and heating rates in the target, while the 3He beam, without optimizing the target geometry, was less favorable, producing about 15% fewer fissions and about 50% higher heating rates than the proton beam at the same beam power.

A helium jet coupled On-Line Isotope Separator Facility at Variable Energy Cyclotron Centre, Kolkata

A helium jet coupled Isotope Separator On Line (ISOL) facility has been designed and developed at Variable Energy Cyclotron Centre (VECC), Kolkata, for the study of nuclei away from the line of β-stability. The 6.2 m long Quadrupole-Quadrupole-Dipole (QQD) system has been designed for a dispersion of 2.52 m for 100% rigidity change. A typical FWHM mass resolving power of around 900 has been measured in high temperature surface ionisation mode. The design and development of the facility and the first test experiment will be reported in this article.

Prescriptions for optimizing intensities of short-lived RIBs at ISOL based research facilities

In order to generate useful intensities of short-lived radioactive species at Isotope Separator On-Line (ISOL) based research facilities, species of interest must be diffused from the interior of the production target-material, effusively transported to an ion source, ionized, extracted, mass-analyzed, and accelerated to research energies in times commensurate with their lifetimes. The intensities at such facilities are principally limited by decay losses associated with times required for diffusion-release from target materials and transport from the target to the ion source and by the maximum permissible primary beam power depositional density that can be tolerated without deleteriously affecting target integrity or ion source efficiency. Consequently, it is imperative to minimize delay times associated with the independent diffusion and effusive-flow processes by choosing small dimensioned (short-diffusion length) highly refractory target materials and formatting them in highly permeable mechanically and thermally robust structures that can withstand high-power beam irradiation for extended periods of time. This article provides basic information on methods, procedures and principles for selecting target materials; for designing fast diffusion-release targets; for designing fast effusive-flow vapor transport systems; and introduces methods for controlling target temperatures as required for optimizing intensities of short-lived radioactive ion beams at ISOL based research facilities.

Chemical investigations of isotope separation on line target units for carbon and nitrogen beams

Radioactive ion beams (RIBs) are of significant interest in a number of applications. Isotope separation on line (ISOL) facilities provide RIB with high beam intensities and good beam quality. An atom that is produced within the ISOL target will first diffuse out from the target material. During the effusion towards the transfer line and into the ion source the many contacts with the surrounding surfaces may cause unacceptable delays in the transport and, hence, losses of the shorter-lived isotopes. We performed systematic chemical investigations of adsorption in a temperature and concentration regime relevant for ISOL targets and ion source units, with regard to COx and NOx on Al2O3 and SiO2. These materials are potential construction materials for the above-mentioned areas. Off-line and on-line tests have been performed using a gas thermochromatography setup with radioactive tracers. The experiments were performed at the production of tracers for atmospheric chemistry (PROTRAC) facility at the Paul Sche...

Status report of the radioactive ion beam production at TRIUMF (invited)

The ISAC radioactive ion beam (RIB) facility has been operational since November 1998. The ISAC Facility at TRIUMF utilizes up to 100μA proton intensity at 500MeV from the existing H− cyclotron to produce RIB using the isotopic separation on-line (ISOL) method. The science programs at ISAC range from nuclear astrophysics to fundamental symmetry. The facility can deliver RIB to the low energy area and a linear accelerator composed of a four-rod radio frequency quadrupole and a linear accelerator can provide beam from A=3to30amu with an energy range from 0.15to1.5AMeV. An accelerator upgrade is underway and will allow us to extend the mass range to A=150amu and the energy up to 6.5AMeV. The target/ion source assembly and heavy-ion optics components are located in a shield canyon under 2m of steel shielding allowing high proton beam intensity on a thick target. At the beginning the production target was operating at 2–5μA but rapidly the proton beam intensity was raised to 40μA. Now, we operate up to nearly 100μA proton beam using the new high power target design equipped with radial fins. While the production target capabilities have improved quite a lot, from 2to100μA, the ion sources development have not followed the same trend. Since the beginning of ISAC most of the RIB production is done using the surface ion source. A 2.45GHz electron cyclotron resonance ion source (ECRIS) was built and used on line with moderate success.

High-efficiency target ion sources for radioactive ion beam generation

In this report, high-temperature ion sources are described, which have demonstrated the high ionization efficiency, species versatility, and operational reliability required at isotope-separator-online (ISOL) based radioactive ion beam facilities such as the Holifield Radioactive Ion Beam Facility (HRIBF). Specific attention is given to the ion optics, operational parameters, thermal transport properties, emittances, and ionization efficiencies of the HRIBF ion sources that have been carefully designed for safe handling in the high-level radiation fields incumbent at such facilities. Included in the article are descriptions and performance data for high-temperature, positive- (electron impact and surface ionization) and negative- (kinetic ejection and surface ionization) ion sources as well as low-temperature, batch-mode negative-ion sources, developed for processing long-lived isotopes that have been the principal contributors to recent successes held at the Holifield Radioactive Ion Beam Facility.

Opportunistic mass measurements at the Holifield Radioactive Ion Beam Facility

A technique for measuring mass differences has been developed at the Holifield Radioactive Ion Beam Facility (HRIBF) that requires no specialized equipment. Mass differences are measured as position differences between known and unknown-mass isobars, dispersed at the image of the energy-analyzing magnet following the 25 MV tandem post-accelerator, and identified by an energy-loss measurement. The technique has been demonstrated on neutron-rich 77–79Cu and 83–86Ge isotopes produced using the isotope separator online (ISOL) method with the 238U(p,fission) reaction, where a mass accuracy of 500 keV was achieved. These nuclides are well suited to the measurement technique, as they readily migrate out of the production target and to the ion source and comprise the most neutron-rich elements of the isobarically mixed beam. Because modest precision mass values can be obtained with only a few tens of counts of the nuclide of interest among orders of magnitude more of the isobaric neighbors closer to stability, the sensitivity of this technique makes it appropriate for initial mass measurements far from stability.

Design of LINAC post-accelerator for VECC RIB facility using realistic field

Variable Energy Cyclotron Centre (VECC) is presently developing an Isotope Separator On-Line (ISOL) post-accelerator type of Radioactive Ion Beam (RIB) facility. The facility is planned around the existing K = 1 3 0 room temperature cyclotron as the primary accelerator and RFQ and LINAC as the post-accelerators for the ion beams. The following report presents the beam dynamics design of the first three LINAC cavities to accelerate RIBs up to about 400 keV/u along with the results of the RF structure studies on the cold model of the first LINAC tank. The mechanical engineering design aspects of the first LINAC tank have also been discussed.