P.J. Billquist

Calcium-41 concentration in terrestrial materials: prospects for dating of pleistocene samples

Calcium-41 has been suggested as a new tool for radiometric dating in the range of 105 to 106 years. The concentration of cosmogenic calcium-41 in natural samples of terrestrial origin has now been determined by high-sensitivity accelerator mass spectrometry after pre-enrichment in calcium-41 with an isotope separator. Ratios of calcium-41 to total calcium between 2 x 10-14 and 3 x 10-15 were measured for samples of contemporary bovine bone and from limestone deposits. Some prospects for the use of calcium-41 for dating Middle and Late Pleistocene bone and for other geophysical applications are discussed.

Half-life of 60Fe

Abstract The half-life of 60Fe has been measured to be T 1 2 = (1.49 ± 0.27) × 10 6 a, significantly longer than the one previous measurement of Roy and Kohman which reported a value of 3 × 105 a uncertain by a factor of 3. The present value was obtained from measurements of specific activity and radioisotope concentration in a material produced by spallation of copper with 191 MeV protons. 60Fe/Fe ratios in the range of 10−8 were measured with the Argonne FN tandem-superconducting linear accelerator system in conjunction with an Enge split-pole spectrograph. The specific activity of 60Fe in Fe was measured through the grow-in of the 1.332 MeV gamma-ray line of the 60Co daughter activity.

Ion plasma sputtering as a method of introducing solid material into an electron cyclotron resonance ion source

A direct ion plasma sputtering effect has been observed in an electron cyclotron resonance ion source and developed into a reliable and simple method for producing ion beams from some solid materials. We describe the ion sputtering technique used with the Argonne Tandem Linac Accelerator System Positive Ion Injector Electron Cyclotron Resonance ion source to produce, to date, stable beams of nickel, silver, tellurium, gold, lead, and bismuth and present the results obtained in test cases.

Long-lived noble gas radionuclides

Abstract The first AMS measurements of 39Ar and 81Kr have been performed by combining positive-ion production in an ECR ion source with acceleration to 6 MeV/A in the ATLAS linear accelerator and detection in a gas-filled spectrograph. Sensitivities of 39Ar/Ar = 8 × 10−16 (natural argon), and 81Kr/Kr = 2 × 10−10 (neutron-activated krypton) were achieved. A full-stripping experiment for 81Kr-81Br separation at 45 MeV/A was performed with the MSU K1200 cyclotron. Substantial contributions from nuclear reactions in a Be stripper foil were observed, in the attempt to detect 81Kr36+ ions in the A1200 recoil separator. The general situation for the detection of noble gas radionuclides is discussed.

Accelerator mass spectrometry at ATLAS

Abstract The special conditions required to run AMS experiments at a large heavy-ion accelerator such as ATLAS are discussed. Operational schemes for the current tandem-linac combination and their application to measurements of the long-lived radioisotopes 41 Ca, 60 Fe and 126 Sn are described. A brief outlook of future possibilities for AMS experiments with the new positive ion injector of ATLAS is presented.

Time evolution of charge states in an electron cyclotron resonance ion source (abstract)a)

The production of high charge‐state ions in an electron cyclotron resonance ion source has been studied as a function of time using a pulsed Nd:YAG laser to ablate heavy metal (bismuth) ions into the plasma. The time required to produce a charge state has been measured by observing the arrival time of the ions at a Faraday cup after the source analyzing magnet. The results of these measurements have been compared to a simple sequential ionization model and are found to be in good agreement with the data. The data can be used to characterize the plasma electron density, electron temperature, and neutral atom density, since these are the only three adjustable parameters in the model and are sufficient to achieve good agreement for the time evolution of all observed charge states.

The positive-ion injector of ATLAS: Design and operating experience

Abstract The recently completed positive-ion injector for the heavy-ion accelerator ATLAS is a replacement for the tandem injector of the present tandem-linac system. Unlike the tandem, the new injector provides ions from the full range of the periodic table. The concept for the new injector, which consists of an ECR ion source on a voltage platform coupled to a very-low-velocity superconducting linac, introduces technical problems and uncertainties that are well beyond those encountered previously for superconducting linacs. The solution to these problems and their relationship to performance are outlined, and experience in the operation of ATLAS with its new injector is discussed.

Studies towards a method for radiocalcium dating of bones.

The authors made preliminary AMS measurements of [sup 41]Ca/Ca ratios in bone and limestone specimens with the Argonne Tandem-Linac Accelerator System (ATLAS). They were able to avoid pre-enrichment of [sup 41]Ca used in previous experiments due to a substantial increase in Ca-beam intensity. Most of the measured ratios lie in the 10[sup [minus]14] range, with a few values below 10[sup [minus]14]. In general, these values are higher than the ones observed by the AMS group at the University of Pennsylvania. They discuss possible implications of these results. They also present the current status of half-life measurements of [sup 41]Ca and discuss [sup 41]Ca production processes on earth.

A new 14 GHz electron-cyclotron-resonance ion source for the heavy ion accelerator facility ATLAS

A 14 GHz electron-cyclotron-resonance (ECR) ion source has been designed and built at Argonne National Laboratory. The source is a modification of the AECR [D. J. Clark, C. M. Lyneis, and Z. Q. Xie, 14th Particle Accelerator Conference (PAC), IEEE Conference 91 CH3038-7, 1991 (unpublished), p. 2796 and C. M. Lyneis, Z. Q. Zie, D. J. Clark, R. S. Lam, and S. A. Lundgren, 10th International Workshop on ECR Ion Sources, Oak Ridge, ORNL CONF-9011136, 1990 (unpublished), p. 47.] at Berkeley and incorporates the latest results from electron-cyclotron-resonance (ECR) developments to produce intense beams of highly charged ions, including an improved magnetic confinement of the plasma electrons with an axial mirror ratio of 3.5. The aluminum plasma chamber and extraction electrode as well as a biased disk on axis at the microwave injection side donate additional electrons to the plasma, making use of the large secondary electron yield from aluminum oxide. The source is capable of ECR plasma heating using two diff...

Operating experience with the Argonne PIIECR ion source system

The Argonne PIIECR ion source is the first ECR ion source system to operate on a high‐voltage (350 kV) platform. The system is the injector into a new superconducting linac which will eventually provide beams over the entire periodic table, including uranium. The experience we have had with the system to date will be discussed. Emphasis will be placed on the source performance with solid materials and the initial performance of the system as an injector to the superconducting linac. The bunching system which is part of the overall source system allows a determination of the system longitudinal emittance. Results of these initial measurements will be presented.