G. D. Alton’s research while affiliated with Oak Ridge National Laboratory and other places

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Publications (280)


A positive (negative) surface ionization source concept for RIB generation
  • Article

6 Reads

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1 Citation

G. D. Alton

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A novel, versatile, new concept, spherical-geometry, positive (negative) surface-ionization source has been designed and fabricated which will have the capability of generating both positive- and negative-ion beams without mechanical changes to the source. The source utilizes a highly permeable, high-work-function Ir ionizer (Ïâ¼ = 5.29 eV) for ionizing highly electropositive atoms/molecules; while for negative-surface ionization, the work function is lowered to Ï â¼ = 1.43 eV by continually feeding cesium vapor through the ionizer matrix. The use of Cs to effect low work function surfaces for negative ion beam generation has the potential of overcoming the chronic poisoning effects experienced with LaBâ while enhancing the probability for negative ion formation of atomic and molecular species with low to intermediate electron affinities. The flexibility of operation in either mode makes it especially attractive for RIB applications and, therefore, the source will be used as a complementary replacement for the high-temperature electron impact ionization sources presently in use at the HRIBF The design features and operational principles of the source will be described in this report.



Experimental methods in RIB target/ion source development and characterization

5 Reads

We have developed off-line experimental techniques and apparatuses that permit direct measurement of effusive-flow delay-times and ionization efficiencies for nearly any chemically reactive element in high-temperature target/ion sources (TISs) commonly used for on-line radioactive ion beam (RIB) generation. The apparatuses include a hot Ta valve for effusive-flow delay-time measurements, a cooled molecular-injection system for determination of ionization efficiencies and a gas-flow measurement/control system for introducing very low, well-defined molecular flows into the TIS. Measurements are performed on a test-stand using molecular feed compounds containing stable complements of the radioactive nuclei of interest delivered to the TIS at flow-rates commensurate with on-line RIB generation. In this report, the general techniques are described and effusive-flow delay-times and ionization efficiency measurements are reported for fluorine in an electron-beam-plasma target/ion source (EBPTIS) developed for RIB generation and operated in both positive and negative ion extraction modes.


A combined thermal dissociation and electron impact ionization source for RIB generation
  • Article
  • Full-text available

15 Reads

The probability for simultaneously dissociating and efficiently ionizing the individual atomic constituents of molecular feed materials with conventional, hot-cathode, electron-impact ion sources is low and consequently, the ion beams from these sources often appear as mixtures of several molecular sideband beams. This fragmentation process leads to dilution of the intensity of the species of interest for RIB applications where beam intensity is at a premium. We have conceived an ion source that combines the excellent molecular dissociation properties of a thermal dissociator and the high ionization efficiency characteristics of an electron impact ionization source that will, in principle, overcome this handicap. The source concept will be evaluated as a potential candidate for use for RIB generation at the Holifield Radioactive Ion Beam Facility (HRIBF), now under construction at the Oak Ridge National Laboratory. The design features and principles of operation of the source are described in this article.

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Production of atomic negative ion beams of the Group IA elements

4 Reads

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1 Citation

A method has been developed which enables the direct sputter generation of atomic negative ion beams of all members of the Group IA elements (Li, Na, K, Rb, and Cs). The method consists of the use of sputter samples formed by pressing mixtures of the carbonates of the Group IA elements and 10% (atomic) Cu, Ag, or other metal powder. The following intensities are typical of those observed from carbonate samples subjected to /approximately/3 KeV cesium ion bombardment: Li⁻: greater than or equal to0.5 ..mu..A; Na⁻: greater than or equal to0.5 ..mu..A; K⁻: greater than or equal to0.5 ..mu..A; Rb⁻: greater than or equal to0.5 ..mu..A; Cs⁻: greater than or equal to0.2 ..mu..A. 7 refs., 2 figs., 1 tab.


Element/target-dependent release times and release efficiencies for the proposed OREB facility

4 Reads

Experiments have been initiated which are designed to measure the time release characteristics of stable ion implanted species from selected refractory target materials which are potential candidates for forming radioactive beans at the proposed Oak Ridge Exotic Beam Facility. In this report, we provide thermal time release data and estimates of the efficiencies for releasing Cl from ZrâSiâ and ⁷⁵As, ⁷⁹Br, and ⁷⁸Se from ZrâGeâ. 14 refs., 1 fig., 1 tab.


Figure 2. Scanning electron micrographs of finely-divided powders after milling, ZrC on the left and HfC on the right.
Figure 4. Scanning electron micrographs of various targets made using the paint coating technique (ZrC on the left, CeS in the middle, and Al 2 O 3 on the right).
A New Method for Coating Highly-Permeable Matrices for High-Power ISOL Production Targets

A relatively simple and inexpensive infiltration coating technique has been developed for depositing refractory target materials onto highly-permeable matrices to form short diffusion-length production targets for ISOL applications. The method is based on a suspension of finely divided (φ: ~1 µm) target materials (e.g. carbides, oxides, sulfides, etc.) in a binder to form a paint that can be vacuum infiltrated to uniformly coat the surfaces of highly-permeable, fibrous matrices such as reticulated-vitreous-carbon-fiber (RVCF). The coating operation is followed by thermal treatment under high vacuum conditions to evaporate the binder and, if possible, to sinter the material. The technique has been used to coat RVCF matrices with a number of refractory metal-carbides and metal-oxides for potential use as high power, short diffusion-length spallation and fission production targets at the RIA. Initial on-line tests of a CeS target that was manufactured using this process have been completed. An on-line release measurement of 34 Cl from this CeS target resulted in beam intensities of about 10 4 ions per second and the presence of molecular ions (aluminum chloride) was also confirmed. Inspection of the target material after irradiation showed no damage, indicating that this method can be used to make viable ISOL production targets.


DEVELOPMENT OF A LITHIUM LIQUID METAL ION SOURCE FOR MEV ION BEAM ANALYSIS

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1 Citation

Lithium liquid metal ion *ource* are an attractive complement to the existing gaseous ion sources that are extensively used for ion beam analysis. This is due in part to the high brightness of the liquid metal ion source and in part to the availability of a lithium ion beam. High brightness is of particular importance to MeV ion microprobes which are now approaching current density limitations on targets determined by the ion source. The availability of a lithium beam provides increased capabilities for hydrogen profiling and high resolution Rutherford backscattering spectrometry. This Paper describes the design and performance of a lithium liquid metal ion source suitable for use on a 5MV Laddertron accelerator. Operational experience with the source and some of its uses for ion beam analysis are discussed.


452 RECENT DEVELOPMENTS AT THE HOLIFIELD HEAVY ION RESEARCH FACILITY

7 Reads

The Holifield Heavy Ion Research Facility (HHIRF) accelerator system consists of a 25URC tandem electrostatic Pelletron' and the Oak Ridge lsochronous Cyclotron* (ORIC). The Pelletron was manufactured by the National Electrostatics Corporation (NEC) and placed into routine operation in 1982. It was the first large accelerator to be constructed in a folded configuration. The design terminal potential is 25 MV. To date, 66 isotopes of 36 elements from H to U, have been provided for the experimental program. Of this number, 27 isotopes were provided using ORIC as an energy booster in coupled operation. ORIC was completed in the early 1960s as a versatile accelerator with variable energy for both fight and heavy ions. ORIC was designed as a K = ME/Q* = 100 cyclotron and can operate at K = 105. In the 1960s ORIC was used mostly for light ion production. In the 1970s the experimental program shifted to heavy ions and in the late 197Os, ORIC was modified to be an energy booster for the tandem accelerator using a foil stripping injection system. In 1988, the internal ion source was decommissioned.


Citations (47)


... In fact, the batch-mode technique is one of the early approaches for producing negative ion beams of isotopes with lifetimes longer than a few hours [46][47][48][49][50][51]. A multi-sample Cs-sputter ion source was developed at HRIBF for batch-mode generation of RIBs of long-lived isotopes [52,53]. Chemically active radioactive species are often released from target materials in a variety of molecular forms, for example, fluorine isotopes were found to be released from Al 2 O 3 production targets primarily as AlF. ...

Reference:

Production of negatively charged radioactive ion beams
A Multi-Sample Cs-Sputter Negative-Ion Source
  • Citing Technical Report
  • April 1999

... Several attempts have been made to describe the processes taking place in hot cavity ion sources using computer modelling, especially those based on the Monte Carlo methods. Some of them focused on thermal ionization in the hot cavity [11,22,23], describing the crucial effect of multiple collisions with the walls of the hot cavity, while other papers presented issues such as vapour transport from the bombarded target to the ionizer [24,25] or the release of nuclides from the walls of the ionizer [26,27]. Various shapes of ionizers were considered in the literature; the most popular being tubular [23,[28][29][30], rarely employed spherical or hemispherical [31][32][33], but also conical [34][35][36], and even the most exotic, resembling a kind of mace with spikes [22]. ...

Monte-Carlo simulation of complex vapor-transport systems for RIB applications
  • Citing Article
  • December 2005

Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms

... Several attempts have been made to describe the processes taking place in hot cavity ion sources using computer modelling, especially those based on the Monte Carlo methods. Some of them focused on thermal ionization in the hot cavity [11,22,23], describing the crucial effect of multiple collisions with the walls of the hot cavity, while other papers presented issues such as vapour transport from the bombarded target to the ionizer [24,25] or the release of nuclides from the walls of the ionizer [26,27]. Various shapes of ionizers were considered in the literature; the most popular being tubular [23,[28][29][30], rarely employed spherical or hemispherical [31][32][33], but also conical [34][35][36], and even the most exotic, resembling a kind of mace with spikes [22]. ...

Modeling complex vapor-transport systems using Monte-Carlo techniques: Radioactive ion beam applications
  • Citing Article
  • November 2005

Journal of Vacuum Science & Technology A Vacuum Surfaces and Films

... The principle of the laser wire is based on laser ionization or photodetachment. Laser ionization has been used in various diagnostics, such as combustion, mass spectroscopy, and isotope purification [10][11][12][13]. A schematic illustration of the laser wire H − profile monitor is shown in Fig. 1. ...

An experimental apparatus proposed for efficient removal of isobaric contaminants in negative ion beams
  • Citing Article
  • September 2008

Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms

... VYBIN et al. Various configurations are used to create and hold plasma: multi-cusp [17], min-B type in the configuration with a hexapole [18], min-B type in the "baseball" configuration [19], a simple mirror cell [20], mirror cell with a volume resonance zone [21], and cusp [22]. ...

Initial Testing of the 6 GHz, All-Permanent Magnet, “Volume-Type” ECR ion Source

... This is so-called flat magnetic field profile. Experimentally, this was demonstrated [36] to be an effective method to increase the extracted ion currents. In our simulations, to obtain such the profile it was necessary to calculate the magnetic field with installing two axially symmetric soft-iron rings in addition to the middle coil and two default solenoids. ...

Performances of Volume Versus Surface ECR Ion Sources
  • Citing Article
  • March 2005

... The pulsed spectrum contains only the data taken when the beam was on target. The peak shown at channel 918 is from the 3908 → 1554 keV decay in 19 F initiated by proton capture onto 18 O, while the peak labeled 208 Tl is a common environmental background line. Note that, since the net beam charge accumulated on the target is nearly identical between DC and pulsed data sets, the resonance peak at channel 918 is nearly unchanged. ...

Extraction of space-charge-dominated ion beams from an ECR ion source: Theory and simulation
  • Citing Article
  • May 2004

... Electron cyclotron resonance (ECR) ion source is an essential component of heavy-ion accelerator. For a given design, the intensities of the highly charged ion beams extracted from the source can be increased by enlarging the physical volume of ECR zone [1]. Several models for ECR ion source were and will be constructed depending on their operating conditions [2][3][4]. ...

The ECR volume effect and its consequences
  • Citing Article
  • January 2006

... At the site of Korea Multi-purpose Accelerator Complex (KOMAC), which was established and is being operated since 2013 as one of branches in the Korea Atomic Energy Research Institute (KAERI), we initiated a research project to develop a radioactive ion (RI) beam facility dedicated for a β -NMR facility based on a 100-MeV proton linear accelerator. Several nuclides, 8 Li, 11 Be, 12 B, 15 O, and 19 O, are known for RI probes for the β -NMR studies [1], and 8 Li is the most widely used β -NMR probe among them. In this endeavour, we developed the prototype of a targetion-source (TIS), which is basically an isotope separation on-line (ISOL) target system for RI beam productions, for the development of a 8 Li beam and demonstrated the production of the 8 Li beam through on-line experiments at KOMAC. ...

Simulation of rare isotope release from ISOL target
  • Citing Article
  • August 2010

Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment

... The generation of high-power chaotic microwave radiation is of interest for a number of applications associated with plasma heating. [4][5][6] We also recognize investigations focused on ensuring secure communication using chaotic signals. This includes studies based on vacuum microwave electronic devices. ...

Electron heating with broadband microwave radiation: A new method for improving the performances of conventional B-minimum electron cyclotron resonance ion sources
  • Citing Article
  • August 2007

Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms