High-intensity Ion Source Research Articles

Intercomparison of High-Precision ∆14C Analyses Using Gas Counting and AMS

We report results of a three-year intercomparison experiment between the WHOI Radiocarbon Laboratory (now at University of California, Irvine) and the NSF-University of Arizona AMS Laboratory. The purpose of this study was to compare high-precision measurements of samples obtained routinely using gas proportional counting techniques with results obtained using AMS techniques. Three sets of annually banded, modern coral samples were used for the intercomparison. Each sample was acidified to CO2 at WHOI and split into two fractions. The larger fraction was converted to acetylene gas and counted at WHOI in quartz, gas-proportional beta counters. The smaller fractions were converted to graphite and analyzed for 14C using AMS techniques at the University of Arizona. Results of the three sample sets are presented. Except for a single outlier, the data from the two laboratories are in good agreement. Of the 13 samples in the third set of the intercomparison, for which a new high-intensity ion source was in operation at the Arizona AMS laboratory, agreement of results is excellent. This finding indicates that measurements made with precisions of < 3% are reproducible at both laboratories.

Accelerator mass spectrometry at Peking University: experiments and progress

The Peking University accelerator mass spectrometer (PKUAMS) has been put into routine operation. 14C measurements of archaeological samples with fast cycling injection have shown good results. The new multi-target high-intensity sputtering ion source has been tested and 10Be measurements were carried out with a new detector in which both the stopping of the intense flux of 10B ions and the identification of 10Be ions are performed. 26A1 samples were also measured. While various applications show good prospects for PKUAMS, further upgrade is desirable.

A multisample, high-intensity Cs sputter negative ion source for accelerator mass spectrometry applications

The development of a high-intensity Cs sputter negative ion source has been completed. The source is equipped with a spherical tungsten ionizer and a target wheel with 18 sample positions. The wheel is separated from the hot sputter region by a gate valve in order to change the samples rapidly and reduce cross contamination. A drive system can push the selected sample into the sputter position and pull it back to the wheel. A metal-ceramic bonded ring is used to support all the parts at sputter potential. The ring is protected from vapor depositions by a specially designed shielding structure, resulting in reliable insulation between the ionizer and the sputter samples. No insulation trouble has occurred during the work for over one year. Beams of 10-μA BeO−, 5-μA Al−, 4.5-μA Fe−, and 350-μA C−, etc. have been delivered. The normalized beam emittance ranges from (2–4) πmm mrad MeV1/2. The memory effect has been evaluated. More than 1000 and 500 times of attenuation for C− and BeO− are observed, respectively, in 10 min after a sample change. The ionization efficiency for 12C− is higher than 5.4% for a graphite sample.

Progress in AMS Measurements at the LLNL Spectrometer

We report on the present status of the Lawrence Livermore AMS spectrometer, including sample throughput and progress towards routine 1% measurement capability for 14C, first results on other isotopes and experience with a multisample high-intensity ion source.

Studies of hydrogen ion beam cleaning of silicon dioxide from silicon using in situ spectroscopic ellipsometry and x-ray photoelectron spectroscopy

The removal of a thin oxide layer from a silicon substrate without significant damage has been achieved at temperatures as low as 500 °C using a low-energy hydrogen ion beam produced by a high-intensity and low-energy ion source in a high-vacuum system. In situ spectroscopic ellipsometry was found to be a sufficiently sensitive and nondestructive method for simultaneously monitoring silicon surface cleaning and ion-induced substrate damage. This letter reports the optimum cleaning parameters for silicon (i.e., minimum ion-induced damage with maximum etch rate of SiO2) to be 300 eV ion beam energy, 60° beam incidence, and 500 °C substrate temperature.

The AMS program at the University of Rochester

The AMS program at the University of Rochester is described with mention of the development of a gas-filled magnet isobar separator as a means to overcome the anticipated problems with high sulfur in 36Cl measurements once a high-intensity ion source is installed. 36Cl is the radioisotope with the largest nubmers of samples measured in recent years. A brief overview of 36Cl and 129I applications as well as other projects is given with details to be found in other contributions in this issue.

A high-intensity multisample Cs sputter source

We have developed a high-intensity Cs sputter negative ion source with a very simple layout of potentials and with multisample capability. The design and present performance of the prototype source are described and possible improvements are discussed.

The gas-filled magnet: An isobar separator for accelerator mass spectrometry

The most difficult problem for accelerator mass spectrometry is the rejection of stable atomic isobars. The intensity of isobaric interference is expected to become a problem for 36Cl measurements with the use of new high-intensity ion sources. Although better chemical separation may be possible through improved sample preparation, the device expected to help most with this problem is the gas-filled magnet. We tested a gas-filled Enge split-pole spectrograph combined with a multiplate gas ionization detector for the separation of 36S from 36Cl and obtained an isobar separation of about two orders of magnitude better than that possible with the detector alone.

AMS of 41Ca Using the CaF3 Negative Ion

High-intensity ion sources are now capable of producing negative molecular ion beams of Ca of >2μA (Middleton et al, 1989). This and the advanced status of 41Ca AMS at several laboratories (Pennsylvania, Argonne National Laboratory, Rochester, Munich, Weizmann Institute) have revived interest in 41Ca (T1/2 = 1.0×105 yr (Mabuchi et al, 1974)) as a possible dating tool (Yamaguchi, 1963; Raisbeck & Yiou, 1979; Kubik et al, 1986).

Construction of a simple low-energy high-intensity gas ion source with a multiaperture extractor system

The gas ion source described is useful for a wide range of applications. It is versatile and easy to optimise by changing various geometrical and/or electrical parameters. The source is used as part of an existing apparatus and typical working parameters are presented together with its performance.

Three‐stage Roots high vacuum pump

A three‐stage Roots pump which has geometrical displacements of 305, 100, and 33 l/s is designed to extend the operating pressure region from 10 to 10−4 Pa. Mechanical features of the Roots pump are coaxial three‐stage design with minimum clearance seals for intermediate sealing between the first, second, and third stages without a lubricant; and computer designed flat‐waist‐cocoon shape rotors which enable more precise machining and narrower rotating clearances. To meet the requirement of hydrocarbon‐free pumping for many modern applications, especially sputtering, ion plating, and high intensity ion sources, a high throughput for different gases must be achieved occasionally at a higher pressure beyond the operating range of turbomolecular or diffusion pumps. The subject Roots pump has pumping speed of 220 and 260 l/s for nitrogen and helium, respectively, at 4100 rpm in the range of 1.3×10−3 to 4.0 Pa at the intake. The compression ratio is 104 for hydrogen, helium, and nitrogen, and an ultimate pressure is 1.3×10−4 Pa without bakeout.

Duoplasmatron Type Source with Cold Cathode

The duoplasmatron is widely used as a high-intensity ion source. The LINAC I-2, which is the injector of a 10 GeV PS, uses a duoplasmatron with a cold cathode. The initial cathode was a heated tantalum filament which was placed in a hollow tantalum cylinder with a wall thickness of 0.1--0.5 mm. It was subsequently discovered that it was not necessary to heat the filament in order to maintain the arc discharge and therefore the filament was used only for source bakeout. Now a thin-wall tantalum cylinder is used as the cathode. The cathode lasts up to 6000 h, requiring replacement approximately once a year.

Pulsed Gas Shutter

To reduce the heavy gas load of the high-intensity duoplasmatron ion source, a rotating disk pulsed gas shutter has been constructed and tested on a test vacuum chamber. The gas shutter is to be installed at the nozzle of the duoplasmatron. The timing of periodic opening is synchronized to an external 20 Hz master pulse. Since the average Q-value has been reduced from 2.8×10-2 Torr·1/sec to 2.8×10-3 Torr·1/sec, it is possible to replace a large pumping by a one-order smaller one.

A Small "Cold-Cathode" High-Intensity Cyclotron Ion Source

High beam currents have been achieved with a radial source which fits into the 2-inch gap of a 30-inch cyclotron. The geometry is that of a cold-cathode or P. I. G. source. However, the cathodes are heated to thermionic temperatures by ion bombardment rather than a conventional high-current heated filament. The source is now in use and produces intense beams of H+, D+, He3, and alpha particles. Internal beams of H+ or D+ of more than one mA are obtained routinely at extraction radius. In addition, 30 ?A of H- or D- are obtained at a stripping foil by merely reversing the magnetic field of the cyclotron.

Recent Developments in High Intensity Ion Beam Production and Preacceleration

Some high intensity ion sources, applicable for particle accelerators, are evaluated in terms of extracted beam emittance and source "brightness". Specifically recent results obtained with the duoplasmatron ion source, with and without large plasma expansion cup, are given. It is indicated that a high intensity "rectilinear" ion beam may be obtained from an expanded plasma with a high gradient accelerator structure. Recent approaches to air insulated columns are given, mainly related to the BNL preaccelerator design.

A pulsed ion source with low gas flowrate

This paper describes the development of a high-intensity pulsed ion source with a low flowrate for the working gas. Various designs were elaborated, and studies were made of two variants of a titanium source with deuterium-loaded electrodes (washers). The deuteron beam current at the 10 mm diameter collector spaced 120 cm from the source was 10 mA. The gas flowrate per pulse was 10−3 cm3. The duration of a current pulse was ∼500 μsec. The pulse repetition rate was several pulses per minute.

A low gas consumption pulsed ion source

The working characteristics of a high-intensity pulsed ion source with low gas consumption are presented. Two different versions of a titanium source with deuterium-impregnated electrodes (disks) have been developed and tested. The deuterium beam current arriving at a 10 mm dia. collector placed 120 cm from the source reached a value of 10 mA. The gas consumption per pulse is 10-3 cm3. The pulse duration is similar 500 μsec and the repetition frequency is several pulses per minute.

Pulsed high-intensity ion source: Part II

Pulsed high-intensity ion source: Part II

Pulsed high-intensity ion source: Part I

The first part of this publication deals with the limitations of the discharge current, extraction of ions and focusing of large ion current beams. Three types of ion sources are described and their data are given. The second part †† deals with detailed investigation of the characteristics of the discharge of the Penning type. For this purpose a special ion source was build which allowed for the exchange of all inner parts.

A new type of high intensity ion source

A new type of high intensity ion source