ANSTO :: Browsing by Author "Lawson, EM"

Browsing by Author "Lawson, EM"

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14C AMS measurements of the bomb pulse in N- and S- hemisphere tropical trees
(Elsevier, 1997-03-02) Murphy, JO; Lawson, EM; Fink, D; Hotchkis, MAC; Hua, Q; Jacobsen, GE; Smith, AM; Tuniz, C
The 14C bomb-pulse signature has been measured by AMS on cross-dateable teak samples from N- and S-hemisphere locations in the tropics. Excellent agreement is found with the atmospheric 14C content in the period 1955 to 1980 for the respective hemispheres. These results demonstrate that 14C measurements can be used to facilitate growth rate determinations in tropical trees. © 1997 Elsevier B.V.
14C analyses at the ANTARES AMS Centre: dating the log coffins of northwest Thailand
(Elsevier, 1994-06-03) Hotchkis, MAC; Fink, D; Jacobsen, GE; Lawson, EM; Shying, ME; Smith, AM; Tuniz, C; Barbetti, M; Grave, P; Quan, HM; Head, J
Recent results of 14C analyses at the ANTARES AMS Centre are presented. Test measurements of 14C blanks demonstrate an ultimate sensitivity of the order of 10−15 (14C/12C ratio). Measurements of unknowns have been made with a precision in the range 1–1.5% using a “slow cycling” mode of operation where the injection magnet field is changed to inject 14C and 13C alternately. Results are presented for a series of log coffins from cave burials in NW Thailand. © 1994 Elsevier B.V.
14C in uranium and thorium minerals: a signature of cluster radioactivity?
(Springer Nature, 1999-06-01) Bonetti, R; Guglielmetti, A; Poli, G; Sacchi, E; Fink, D; Hotchkis, MAC; Jacobsen, GE; Lawson, EM; Hua, Q; Smith, AM; Tuniz, C
Various uranium and thorium minerals have been analysed with accelerator mass spectrometry to determine their 14C content. It is found that, whenever the contribution from secondary reactions such as the 11B(α,p)14C is sufficiently low, the 14C concentration is consistent with that expected from 14C (spontaneous) cluster radioactivity from radium isotopes of the uranium and thorium natural series. © Springer-Verlag 1999
AMS at ANTARES – the first 10 years
(Elsevier, 2000-10) Lawson, EM; Elliott, G; Fallon, J; Fink, D; Hotchkis, MAC; Hua, Q; Jacobsen, GE; Lee, P; Smith, AM; Tuniz, C; Zoppi, U
The status and capabilities of the ANTARES AMS facility after 10 years are reviewed. The common AMS radioisotopes, 10Be, 14C, 26A1, 36C1 and 129I, are routinely analysed. A capability for the detection of 236U and other actinide isotopes has been developed. The measurement program includes support to Quaternary science projects at Australian universities and to ANSTO projects in global climate change and nuclear safeguards. © 2000 Elsevier Science B.V.
AMS radiocarbon analysis of microsamples
(Australian Institute of Nuclear Science and Engineering, Australian Nuclear Science & Technology Organisation and Australian Museum, 1997-02-12) Jacobsen, GE; Hua, Q; Tarshishi, J; Fink, D; Hotchkis, MAC; Lawson, EM; Smith, AM; Tuniz, C
The ANTARES AMS Centre has two chemistry laboratories dedicated to preparing targets for measurement. Target preparation encompasses a variety of activities ranging from the curation of incoming samples to the numerous steps involved in the purification and processing of dissimilar samples. One of the two laboratories is set up for the physical and chemical pretreatment of 14C samples. Treatments include cleaning by sonification, sorting, grinding and sieving, and chemical treatments such as the standard AAA treatment, and solvent extraction. Combustion and graphitisation are also carried out in this laboratory. The second laboratory is a clean room and is dedicated to the combustion, hydrolysis and graphitisation of 14C samples as well as processing targets for the other isotopes. Combustion is achieved by heating the sample to 900 deg C in the presence of CuO, the resulting gas is purified by passing over Ag and Cu wire at 600 deg C. Graphitisation is carried out by reducing the CO{sub 2} with an iron catalyst (600 deg C) in the presence of zinc (400 deg C) and a small amount of hydrogen. Samples such as charcoal, shell, bone, wood, sediment, seawater and groundwater, containing 0.3-1 mg or more of original carbon, are processed routinely for radiocarbon analysis. The current 14C chemistry background for 1 mg carbon is approx. 0.3 percent of modern carbon (pMC) enabling materials` dating up to 45 000 BP.
AMS support for Australian prehistory research
(Australian Institute of Physics, 1998-04-01) Lawson, EM
The major use of ANTARES is Accelerator Mass Spectrometry (AMS) with 14C being the most commonly analysed radioisotope - presently about 35% of the available beam time on ANTARES is used for 14C measurements. The accelerator measurements are supported by, and dependent on, a strong sample preparation section. The ANTARES AMS facility supports a wide range of investigations into fields such as global climate change, ice cores, oceanography, dendrochronology, anthropology, and classical and Australian archaeologgy. Described here are some examples of the ways in which AMS has been applied to support the research into the archaeology, prehistory and culture of this continent's indigenous Aboriginal peoples.
The ANTARES AMS Centre : a status report
(Cambridge University Press, 2016-07-18) Tuniz, C; Fink, D; Hotchkis, MAC; Jacobsen, GE; Lawson, EM; Smith, AM; Hua, Q; Drewer, P; Lee, P; Levchenko, VA; Bird, R; Boldeman, JW; Barbetti, M; Taylor, G; Head, J
The ANTARES accelerator mass spectrometry facility at Lucas Heights Research Laboratory is operational and AMS measurements of 14C, 26Al and 36Cl are being carried out routinely. Measurement of 129I recently commenced and capabilities for other long-lived radioisotopes such as 10Be are being established. The overall aim of the facility is to develop advanced programs in Quaternary science, global climate change, biomedicine and nuclear safeguards. © the Department of Geosciences, The University of Arizona
The ANTARES AMS Centre at the Lucas Heights Research Laboratories
(Elsevier, 1994-06-03) Tuniz, C; Fink, D; Hotchkis, MAC; Jacobsen, GE; Lawson, EM; Smith, AM; Bird, JR; Boldeman, JW
The ANTARES AMS facility at the Lucas Heights Research Laboratories is operational and AMS measurements of 14C and 26Al are performed routinely. Measurement programs for a variety of other long-lived cosmogenic radioisotopes are being implemented on specialised beamlines. The overall aim of the facility is to establish an AMS centre for advanced studies in global change and Quaternary science. Other projects in biomedicine and nuclear safeguards monitoring are also being developed. © 1994 Elsevier B.V.
An attempt to detect electrochemical doping of silicon with arsenic by Rutherford backscattering analysis
(Australian Atomic Energy Commission, 1983-02) Tavendale, AJ; Lawson, EM
Rutherford scattering analysis with 2.0 MeV 4He+ ions failed to detect doping of silicon substrates with arsenic following cathodic electroplating. This is in contrast with the claims of J. Antula [J. Appl. Phys., 48:2581, 1977] that electromigration leads to the formation of n-type, arsenic-doped, near-surface layers in silicon. Arsenic was detected only in the surface oxide layer formed during plating. Complementary thermoprobe measurements also showed no doping effects in the silicon substrates.
The behaviour of high purity semiconductor surface-barrier nuclear radiation detectors at low temperatures
(Australian Atomic Energy Commission, 1973-04) Lawson, EM; Tavendale, AJ
The characteristics of a germanium and a silicon surface barrier detector have been examined at low temperatures (78 to 5 K). Preliminary results have also been obtained from a gallium arsenide detector. All detectors were fabricated from high purity material. Below some critical temperature (10 K in germanium and 32 K in silicon) the spectral response to y-rays deteriorated markedly, particularly for low bias. Near liquid helium temperature best resolutions of 10.0 keV at 662 keV and 3.0 keV at 122 keV were obtained with the germanium and silicon detectors respectively. Relative efficiency measurements found no change in the sensitive depth with temperature in contrast to the indications of the capacitance. A model based on field-assisted detrapping is proposed to account for the fact that sensitive depth is independent of temperature. The behaviour of the capacitance and the existence of slow components in the pulse risetime are explained in terms of the equivalent circuit of the detector. The energy resolution of the gallium arsenide detector did not change on cooling to 7 K where a resolution of 3.9 keV at 60 keV was measured.
The chronology of the Late Neolithic and Early Chalcolithic periods in the north Jordan Valley: new 14C determinations from Pella in Jordan
(Oxford University School of Archaeology, 2002-04-09) Bourke, S; Lawson, EM; Hua, Q; Zoppi, U
Not available
Equipment and methodology for high precision, high throughput 14C AMS analyses at ANTARES
(Elsevier, 1994-06-03) Smith, AM; Fink, D; Hotchkis, MAC; Jacobsen, GE; Lawson, EM; Shying, ME; Tuniz, C; Watt, GC; Fallon, J; Ellis, PJ
The original Rutgers FN tandem accelerator has been modified for high-precision high-throughput AMS analyses at the ANTARES AMS Center. The status of this work and future plans are discussed, with emphasis on 14C. Isotopic ratios are measured at ANTARES by sequentially injecting stable isotopes and the radioisotope, and the systems developed for this purpose are described. Progress with a new injection platform and high intensity, multi-sample ion source is also given. © 1994 Elsevier B.V.
First 26Al analyses at the ANTARES AMS Centre: uptake via oral ingestion of 26Al in rats
(Elsevier, 1994-06-03) Fink, D; Walton, J; Hotchkis, MAC; Jacobsen, GE; Lawson, EM; Smith, AM; Tuniz, C; Wilcox, D
As the debate on the role played by aluminium in Alzheimer's disease remains a controversial one, the mechanism and degree of uptake of aluminium into brain tissue is not well understood nor quantified. We report here results from the initial phase of our study of aluminium uptake and retention in tissues of rats following oral administration of a tracer dose of 26Al. An account of our biomedical findings in old rats will be described elsewhere. For a young rat population, we find 26Al retention in the liver to be 7 times that in the brain. A description of our experience in performing aluminium measurements of biological tissues is described and interpretation of the findings are given. © 1994 Elsevier B.V.
High-precision radiocarbon measurements at the ANTARES AMS Centre
(Elsevier, 1996-06-01) Hotchkis, MAC; Fink, D; Hua, Q; Jacobsen, GE; Lawson, EM; Smith, AM; Tuniz, C
The ANTARES AMS Centre at Lucas Heights Research Laboratories is currently used for measurements of the long-lived radioisotopes 14C, 26Al, 36Cl and 129I, with measurement of 10Be and actinides under development. Improved precision for 14C (to 0.5%) has been achieved with the recent commissioning of a 59 sample ion source coupled with automated data acquisition. We have developed rigorous data evaluation methods which are invaluable in assessing reproducibility and aid in the identification of physical problems with the system. Low backgrounds, in the accelerator and in the sample preparation laboratories, have allowed us to measure very old samples (to 50 000 years BP) and are also vital for high-accuracy dating of small samples. © 1996 Elsevier Science B.V.
A large volume, multi-element Ge(Li) spectrometer
(Australian Atomic Energy Commission, 1970-11) Lawson, EM; Tavendale, AJ; Dawson, AC
To make use of the good energy resolution of Ge(Li) spectrometers of r-ray energies of several MeV, the sensitive volume must be increased to beyond 100 cm3. This volume is generally only attainable by operating several smaller spectrometers in parallel. Three coaxial Ge(Li) detectors were fabricated, assembled in a cryostat and operated in parallel. The spectral performance was relative efficiency of this multi-element spectrometer were investigated for r-rays of energies between 1 and 10 MeV. High energy r-rays (5-10 MeV) were obtained by thermalising neutrons from a Pu-Be source and then absorbing them in materials with high cross sections for radiative capture. The experience gained is summarised and alterations to future multi-element spectrometers are proposed.
Measurements of the 14CO2 bomb pulse in firn and ice at Law Dome, Antarctica
(Elsevier, 1997-03-02) Levchenko, VA; Etheridge, DM; Francey, RJ; Trudinger, CM; Tuniz, C; Lawson, EM; Smith, AM; Jacobsen, GE; Hua, Q; Hotchkis, MAC; Fink, D; Morgan, VI; Head, J
14CO2 produced in the atmosphere by nuclear weapons testing in the 1960's is now incorporated in the air bubbles of Antarctic ice. The high atmospheric radiocarbon growth rates through the period of tests and subsequent decline provide a unique and independent test for the smoothing of atmospheric CO2 signals due to firn diffusion and bubble close off. The level of smoothing quantifies the time resolution with which atmospheric trace gas histories can be reconstructed from ice cores. In this paper, the methodologies for the preparation and AMS measurements of ice core and firn 14CO2 from high accumulation sites at Law Dome are detailed. The results are compared with predictions of a numerical model incorporating firn air diffusion and bubble close-off. The sample sizes, precision of measurements and sources of contamination are discussed for both firn and ice samples. © 1997 Elsevier Science B.V.
A method for annealing ion-implanted silicon on a vitreous carbon strip heater
(Australian Atomic Energy Commission, 1983-06) Lawson, EM
A description is given of a simple method for the transient annealing of ion-implanted semiconductors on a vitreous carbon strip heater. Samples of Si implanted with doses of 1-5 x 1015 cm-2 As and Sb ions at 35 or 80 KeV were annealed at temperatures in the range 650-1110oC and for times between 15 s and 2 min. Annealing was confirmed by Rutherford backscattering and electrical measurements. The details of these measurements are explained by taking into account the impurity solid solubility and the maximum as-implanted concentration. Supersaturated solutions of Sb and Si were found in all samples examined in this work. The production of supersaturation by strip heater annealing does not seem to have been reported elsewhere.
The operation near liquid helium temperature of a gold-barrier hyper-pure germanium detector for gamma-rays
(Australian Atomic Energy Commission, 1971-02) Lawson, EM; Tavendale, AJ
Diode characteristics and spectral response to 137Cs γ-rays of a gold-barrier detector made from hyper-pure germanium (net donor concentration 3 x 10 11cm-3) were examined over the temperature range 5 -78°K. Trapping at the primary shallow donor is believed responsible for poor energy resolution at low temperatures. At 5°K a best resolution of 10 keV FWHM was obtained. Efficiency measurements indicate no change in depletion depth on cooling to 5°K with constant bias, in contrast to capacitance measurements. The latter variation, however, can be explained in terms of the response of the detector equivalent circuit to bridge frequency and carrier freeze-out effects. Field-assisted de-trapping at the primary shallow donors is believed responsible for the temperature independent depletion depth and an improvement in resolution with bias in the low temperature carrier freeze-out region (< 10°K).
Preliminary investigations of the formation of laser-doped contacts on semiconductors
(Australian Atomic Energy Commission, 1981-10) Lawson, EM
Contacts formed by laser doping single crystal semiconducting samples have been investigated by a variety of techniques. p- and n-type contacts have been formed on Ge, Si and GaAs by irradiating evaporated surface layers with a Q-switched ruby laser. The contact produced were thin and heavily doped. Techniques used to examine the contacts include Rutherford backscattering, scanning electron microscopy and sheet Hall and resistivity measurements.
A q-switched ruby laser for producing laser-doped contacts to semiconductors
(Australian Atomic Energy Commission, 1982-08) Rose, A; Lawson, EM
A description is given of a q-switched ruby laser used for producing laser-doped contacts on semiconductors.Homogenisation of the laser beam and measurement of the output energy are discussed and some attention is given to the problems of sample reflectivity. A brief outline of the laser-doping process is provided, together with recent experimental results and details relating to the production and analysis of the contacts. A preliminary result of defect characteristics after laser irradiation of germanium is also presented.

Browsing by Author "Lawson, EM"

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