Surface Ionization Ion Source Research Articles

Chemistry of the elements at the end of the actinide series using their low-energy ion-beams

Abstract Studies of the chemical properties of the elements at the uppermost end of the Periodic Table are extremely challenging both experimentally and theoretically. One of the most important and interesting subjects is to clarify the basic chemical properties of these elements as well as to elucidate the influence of relativistic effects on their electronic configuration. Isotopes of these elements produced at accelerators, however, are short-lived, and the number of produced atoms is so small; any chemistry to be performed must be done on an atom-at-a-time basis that imposes stringent limits on experimental procedures. Here we describe our recent achievements in the effective production of low-energy ion-beams of the elements at the end of the actinide series, fermium (Fm, atomic number Z = 100), mendelevium (Md, Z = 101), nobelium (No, Z = 102), and lawrencium (Lr, Z = 103), using a surface ionization ion-source installed in the ISOL (Isotope Separator On-Line) at the Tandem accelerator facility of JAEA (Japan Atomic Energy Agency). Then the successful measurements of the first ionization potentials (IP1) of these elements with the ISOL setup are reviewed. The measured IP1 values increased up to No via Fm and Md, while that of Lr was the lowest among the actinides. Based on the variation of the IP1 values of the heavy actinides with the atomic number in comparison with those of the heavy lanthanides, the results clearly demonstrated that the 5f orbitals are fully filled at No, and the actinide series ends with Lr. Furthermore, the IP1 value of Lr provoked controversy over its position in the Periodic Table, so a short introduction to this issue is presented. The feasibility of the extension of chemical studies to still heavier elements with their ion-beams generated by ISOL is briefly discussed.

Present status of electron-beam-driven RI separator for SCRIT at RIKEN RI Beam Factory

A radioactive isotope (RI) separator named ERIS (electron-beam-driven RI separator for SCRIT) was constructed at the SCRIT (Self-Confining Radioactive isotope Ion Target) electron scattering facility at RIKEN RI Beam Factory and has been in operation since 2013. Recently, ion stacking and pulse extraction were developed at ERIS to improve the dc-to-pulse conversion efficiency of a radio-frequency quadrupole cooler buncher. Using a surface-ionization ion source, long-time stacking inside ERIS was realized and a dc-to-pulse conversion efficiency of more than 50% was achieved with a relatively small amount of buffer gas.

Design Study and Fabrication of the Target/Ion Source to Generate a Li-8 Beam

The Korea Multi-purpose Accelerator Complex (KOMAC) has developed a target/ion source (TIS) to generate a Li-8 radioactive isotope beam. The basic concept of the TIS is that the Li isotope is produced at a beryllium-oxide target irradiated by a 100-MeV proton beam, and Li atoms are ionized at a surface ionization ion source (SIS). Various numerical studies were conducted to design the TIS. The FLUKA code was utilized to estimate the Li-8 production rate and to find an optimum target thickness. Also, a simple Monte Carlo code was developed to estimate the ionization efficiency of the SIS. In addition, a zero-dimensional power balance model of the TIS was developed, and a three-dimensional finite-element method was applied to obtain detailed thermal analysis results. On the basis of the thermal analysis, the related design and operation parameters were determined. The TIS designed by using various numerical studies was fabricated and tested. The TIS will be irradiated by a proton beam and generate Li-8 beam for β-NMR facility.

Development of a He/CdI2 gas-jet system coupled to a surface-ionization type ion-source in JAEA-ISOL: towards determination of the first ionization potential of Lr (Z = 103)

We report on development of a gas-jet transport system coupled to a surface ionization ion-source in the JAEA-ISOL (Isotope Separator On-Line) system. As a new aerosol material for the gas-jet system, CdI2, which has a low boiling point of 713 °C, is exploited to prevent deposition of the aerosol material on the surface of the ion-source. An additional filament is newly installed in the previous ion-source to provide uniform heating of an ionizer. The present system is applied to the measurement of absolute efficiencies of various short-lived lanthanide isotopes produced in nuclear reactions.

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.

First successful ionization of Lr (Z = 103) by a surface-ionization technique

We have developed a surface ionization ion-source as part of the JAEA-ISOL (Isotope Separator On-Line) setup, which is coupled to a He/CdI2 gas-jet transport system to determine the first ionization potential of the heaviest actinide lawrencium (Lr, Z = 103). The new ion-source is an improved version of the previous source that provided good ionization efficiencies for lanthanides. An additional filament was newly installed to give better control over its operation. We report, here, on the development of the new gas-jet coupled surface ion-source and on the first successful ionization and mass separation of 27-s (256)Lr produced in the (249)Cf + (11)B reaction.

Isotope fractionation in surface ionization ion source of alkaline-earth iodides

The relationship between the isotope fractionation of alkaline-earth elements in the surface ionization ion source and the evaporation filament current, i.e., filament temperature, was studied. It was confirmed that the isotope fractionation depends on the evaporation filament temperature; the isotope fractionation in the case of higher temperature of filament becomes larger. The ionization and evaporation process in the surface ionization ion source was discussed, and it was concluded that the isotope fractionation is suppressed by setting at the lower temperature of evaporation filament because the dissociations are inhibited on the evaporation filament.

Simulations of ionization in a hot cavity surface ion source

A new numerical Monte Carlo method based model of a hot cavity surface ionization ion source is presented in this paper. The model, intended to support the studies on ionization phenomena in a widely used class of ion sources, takes into account geometry of the ion source and extraction system, ionizer temperature and other features. The results of ion source efficiency calculations for various configurations of the extraction field are reviewed. The dominant role of the ionizer region near the extraction opening is described. Simulated dependences of ionization efficiency on the working parameters like ionizer length and temperature, ionization potential of the substance, and extraction voltage are discussed. A good agreement of the experimental data (e.g., influence of ionizer temperature, current-voltage curve) and the predictions of the model is found. It is also shown that the contribution to the ionization yield from impact of thermionic electrons accelerated by the extraction field may be significant, especially for the substances of small surface ionization coefficient. The simulation results are compared to the predictions of different theoretical models of the ion source--the obtained simulation data are in accordance both with a well-known Kirchner formula and the so called spherical ionizer model.

Development of electron beam ion source charge breeder for rare isotopes at Californium Rare Isotope Breeder Upgrade

Recently, the Californium Rare Isotope Breeder Upgrade (CARIBU) to the Argonne Tandem Linac Accelerator System (ATLAS) was commissioned and became available for production of rare isotopes. Currently, an electron cyclotron resonance ion source is used as a charge breeder for CARIBU beams. To further increase the intensity and improve the purity of neutron-rich ion beams accelerated by ATLAS, we are developing a high-efficiency charge breeder for CARIBU based on an electron beam ion source (EBIS). The CARIBU EBIS charge breeder will utilize the state-of-the-art EBIS technology recently developed at Brookhaven National Laboratory (BNL). The electron beam current density in the CARIBU EBIS trap will be significantly higher than that in existing operational charge-state breeders based on the EBIS concept. The design of the CARIBU EBIS charge breeder is nearly complete. Long-lead components of the EBIS such as a 6-T superconducting solenoid and an electron gun have been ordered with the delivery schedule in the fall of 2011. Measurements of expected breeding efficiency using the BNL Test EBIS have been performed using a Cs(+) surface ionization ion source for external injection in pulsed mode. In these experiments we have achieved ∼70% injection∕extraction efficiency and breeding efficiency into the most abundant charge state of ∼17%.

Measurements of charge state breeding efficiency at BNL test EBIS

Charge breeding of singly charged ions is required to efficiently accelerate rare isotope ion beams for nuclear and astrophysics experiments, and to enhance the accuracy of low-energy Penning trap-assisted spectroscopy. An efficient charge breeder for the Californium Rare Isotope Breeder Upgrade (CARIBU) to the ANL Tandem Linear Accelerator System (ATLAS) facility is being developed using the BNL Test Electron Beam Ion Source (Test EBIS) as a prototype. Parameters of the CARIBU EBIS charge breeder are similar to those of the BNL Test EBIS except the electron beam current will be adjustable in the range from 1 to 2 A. The electron beam current density in the CARIBU EBIS trap will be significantly higher than in existing operational charge state breeders based on the EBIS concept. The charge state breeding efficiency is expected to be about 25% for the isotope ions extracted from the CARIBU. For the success of our EBIS project, it is essential to demonstrate high breeding efficiency at the BNL Test EBIS tuned to the regime close to the parameters of the CARIBU EBIS at ANL. The breeding efficiency optimization and measurements have been successfully carried out using a Cs + surface ionization ion source for externally pulsed injection into the BNL Test EBIS. A Cs + ion beam with a total number of ions of 5×10 8 and optimized pulse length of 70 μs has been injected into the Test EBIS and charge-bred for 5.3 ms for two different electron beam currents – 1 and 1.5 A. In these experiments we have achieved 70% injection/extraction efficiency and breeding efficiency into the most abundant charge state ∼17%.

A compact radio frequency quadrupole for ion bunching in the WITCH experiment

During the last several years the WITCH (Weak Interaction Trap for CHarged particles) experimental setup at ISOLDE has undergone various upgrades aiming at improvement of general performance. An essential innovation, a compact Radio Frequency Quadrupole (RFQ) ion cooler and buncher device, was designed and successfully commissioned as a part of the off-line tuning system of WITCH. The RFQ is coupled to the existing surface ionization ion source providing high intensity ion bunches (up to 107 ions per bunch) towards the pulsed drift tube and the Penning traps of WITCH. This achievement allows for loading and tuning of the Penning traps in the domain of space charge limits and grants off-line operation independently of the REX-ISOLDE ion source. The current upgrade allows for a more thorough and frequent testing with bunched stable ion beams of high intensities, which will be used for studying various systematic effects involved in experiments with radioactive ions.

Li+ ion emission from a hot-plate alumina-silicate source stimulated by flash heating with an infrared laser

The Neutralized Drift Compression Experiment-II accelerator under construction at Lawrence Berkeley National Laboratory has been designed to employ a lithium-doped alumino-silicate (Al-Si) hot-plate surface-ionization ion source. In order to achieve the design 1 mA∕cm(2) current density, the emitter must be constantly kept at a high temperature, leading to the accelerated loss of Li material as ions or neutrals. As a result, the estimated lifetime of the source is 50 h. This lifetime can be extended if the source is kept at low temperature during standby, and pulse heated to the high temperature during the ion extraction phase only. A pulsed heating technique based on an infrared laser (CO(2) gas discharge, λ = 10.6 μm) is described in this paper. The feasibility of ion current emission stimulated by flash heating with an infrared (IR) laser was demonstrated. High repeatability of the laser-stimulated ion current was observed, creating an opportunity for modulation and gating of the ion current with a laser pulse. It was found that with the available low power (≈115 W∕cm(2)) IR laser, current densities as high as 0.8 mA∕cm(2) could be achieved with a 2.8 mm diameter source. Various approaches for scaling to a larger (10 cm diameter) source and the application of short pulse, high power lasers are discussed. The results and conclusions of this paper may apply to various species of hot-plate ion sources.

The radioactive ion beam production systems for the SPIRAL2 project

The SPIRAL2 project, currently under construction at GANIL, will include an isotope separator on line based facility for the production and acceleration of radioactive ion beams. A superconducting linear accelerator will accelerate 5 mA deuterons up to 40 MeV and 1 mA heavy ions up to 14.5 MeV/u. These primary beams will be used to bombard both thick and thin targets. We are investigating three different techniques to produce the radioactive ion beams: (1) the neutron induced fission of uranium carbide, (2) the direct interaction of deuterons in a uranium carbide target, and (3) the interaction of a heavy ion beam with a target. All these production systems will be coupled to an ion source. Four kinds of ion sources are foreseen for the ionization of the radioactive atoms: an electron cyclotron resonance ion source, a surface ionization ion source, a forced electron beam induced arc discharge ion source, and a laser ion source depending on the characteristics of the desired radioactive ion beam in terms of intensity, efficiency, purity, etc. A presentation of the SPIRAL2 project and of the different production systems is given.

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.

High temperature ion sources with ion confinement

Different types of high temperature ion sources such as surface, laser, and electron beam ionization ion sources have been developed and tested in off-line and on-line experiments. All types of developed ion sources have an essential common feature: an existence of the ion confinement inside the ion source cavity.

Supersonic gas chromatography/mass spectrometry.

A new gas chromatography/mass spectrometry (GC/MS) system was designed and evaluated which we have named 'Supersonic GC/MS'. It is based on a modification of a commercially available GC/MS system to include a supersonic molecular beam (SMB) MS interface. In this system the standard electron ionization (EI) ion source was replaced with a fly-through EI ion source mounted in the path of the SMB. A hyperthermal surface ionization (HSI) ion source combined with a 90 degrees ion mirror (for the EI-produced ions) was also added, and placed inside the quadrupole mass analyzer in place of its original EI ion source. The 'Supersonic GC/MS' system requires 18 cm added bench space plus the addition of an air-cooled 60 L/s diffusion pump and a 537 L/min rotary pump. The system is user friendly since all the gas flow rates, heated zones, sampling and data analysis are performed the same way as the original system and are computer-controlled via the original software. Similar EI sensitivity was obtained as with the original system for hexachlorobenzene and octafluoronaphthalene, while improved EI detection limits were demonstrated for methyl stearate and eicosane due to the significant enhancement of their molecular ion abundances. A GC/MS detection limit of 500 ag for pyrene was demonstrated using HSI. Good supersonic expansion cooling was achieved with large alkanes, despite the use of a rotary pump at the nozzle chamber instead of a diffusion pump. High temperature GC/MS analysis was demonstrated for large polycyclic aromatic hydrocarbons (PAHs) including ovalene and decacyclene (ten rings). Library searches with EI mass spectra are demonstrated, and it is explained why the enhancement of the molecular ion actually improves the library search in most cases. The analysis of large phthalate esters is also described, and the improvement obtained is shown to originate from their enhanced molecular and high mass fragment ions.

A Trial Modification of a Surface Ionization Ion Source for Direct Sample Loading for Isotope Analysis.

A trial modification was carried out to the conventional surface (thermal) ionization ion source. A direct sample loading of milligram sized chip of solid sample completely free from terrestrial chemical additional reagents is adopted in the modification. A milligram sized block sample is set into a kind of boat filament made of tantalum, heated and evaporated in the form of atomic vapor with no addition of silica gel or phosphoric acid. This point is perfectly different from other previous works of direct loading methods. The atoms are ionized at the surface of the side filament made of rhenium. The direct loading ionization system was installed in a virtual image compact double focusing mass spectrometer whose mass resolving power is reached over 5,000. As an example of isotope analysis, a 0.5 mg weighed chip of commercially sold pure magnesium metal was loaded as a sample. It gave reasonable isotope ratio 25Mg/24Mg=0.12472±0.00045 and 26Mg/24Mg=0.13564±0.00050; δ26=0.15‰. Several terrestrial mineral samples, forsterite, enstatite, hypersthene, hornblende, and serpentine were also analyzed for magnesium isotope ratios, and δ26's for those samples were distributed -1.7‰ to +4.9‰. Although the reproducibility of isotope analysis is ±3.5‰, and may be comparatively too large to apply the detection of minute isotope anomaly, the newly developed ion source was found to be usable for the isotope analysis of a milligram sized solid samples by the method of direct loading completely free from the additives of chemical reagents.

Self imaging of surface ionization ion sources — where do the ions come from?

Images of the ion emitting regions of solid state ion sources have been produced using the ions emitted from the sources during operation to help elucidate the chemistry and physics of surface ionization. Examples are presented of a ceramic negative ion source producing perrhenate anions and of a zeolite ion source producing cesium cations, both of which are used as ion emitters in SIMS guns. In both cases it is shown that the ions orginate from the surface of the ceramic or zeolite matrix, and not from interfacial regions between the matrix and the metal support structure. It is argued that for these two systems the gas phase ions are formed predominantly by direct sublimation of preformed ions from the hot surface of the matrix, due to the established fact that the ions observed in the gas phase are also known to exist in the solid, while it is improbable that the neutral species exist in the solid in appreciable concentrations. It is further shown that conventional surface ionization filament designs introduce asymmetric voltage gradients in the ion lens, leading to a loss in focusing. This can be corrected by using an indirectly heated ion source that has no voltage gradient across the face of the ion emitting region.

Beam Bunching at Surface Ionization Ion Source and Its Application

Beam Bunching at Surface Ionization Ion Source and Its Application

Plasma kinetics of magnesium and calcium stable isotope tracers in a human subject after simultaneous oral ingestion of 25Mg and 44Ca determined by thermal ionization mass spectrometry.

The plasma concentrations of stable isotope tracers of magnesium (25Mg) and calcium (44Ca) were determined during a 50 h period, after simultaneous oral tracer ingestion in an adult man. The measurements were performed by magnetic sector field mass spectrometry using surface ionization ion sources. The data were used to evaluate the potential of this method in long-term kinetic studies. It is concluded that under the experimental conditions specified, the isotopic tracers will be detectable in blood plasma with sufficient precision and accuracy for approximately 600 h after oral ingestion. The differences in the plasma concentration curves of 25Mg and 44Ca were analysed by means of the convolution integral method. These differences indicate inhomogeneities in the distribution of absorption activity relative to magnesium and calcium within the upper small intestine.