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Corrections for contamination background in AMS {sup 14}C measurements

Description: Measurements of {sup 14}C/{sup 13}C ratios were made on samples of Oxalic Acid and {sup 14}C dead materials spanning the mass range from 10 {micro}g to {approximately} 1 mg. These measurements have allowed the determination of both the amount, and the {sup 14}C content, of the contaminant carbon introduced during sample processing in the laboratory. These data were used to correct measured {sup 14}C/{sup 13}C ratios obtained from ANU Sucrose and {approximately} one-half-life old test samples for the influence of the contaminant. The test samples spanned the 10 {micro}g to {approximately} 1 mg mass range and the corrections were made using three different formulae. The results obtained from these calculations allow the accuracy of these background correction formulae to be evaluated.
Date: June 1, 1996
Creator: Brown, T.A. & Southon, J.R.
Partner: UNT Libraries Government Documents Department

Center for accelerator mass spectrometry Lawrence Livermore National Laboratory

Description: The Center for Accelerator Mass Spectrometry (CAMS) at Lawrence Livermore National Laboratory (LLNL) is a multi-disciplinary research organization that conducts both technological and applications research. CAMS operates both an HVEC FN tandem and a NEC Model 5SDH-2 tandem accelerator. Using highly sensitive accelerator-based element and isotope detection methods, staff at CAMS collaborate with a broad scope of external and internal researchers to solve problems for LLNL, the University of California, the U.S. Department of Energy, and other academic, government, and industrial laboratories. The HVEC FN tandem is used by the LLNL Accelerator Mass Spectrometry (AMS) group. AMS is a technique that uses isotope ratio mass spectrometry at MeV energies to quantify long lived radioisotopes. For AMS, the FN tandem is operated under a distributed computer control system that makes possible rapid and precise switching between experimental configurations on a daily basis. The accelerator and beam lines are unshielded with radiation protection provided by a computer supervised radiation monitoring system and proximity shielding. With AMS, we routinely measure the isotopes {sup 3} H, {sup 7} Be, {sup 10} Be, {sup 14} C, {sup 26} Al, {sup 36} Cl, {sup 41} Ca, {sup 59} Ni, and {sup 129} I at abundances as low as 1 part in 10{sup 15} . Research programs are as diverse as archaeology, dosimetry of carcinogens and mutagens, oceanic and atmospheric chemistry, paleoclimatology, and detection of signatures of nuclear fuel reprocessing for non-proliferation purposes. During the past year our AMS group has run approximately 20,000 research samples. The NEC Model 5SDH-2 tandem accelerator is used by the Ion Micro Analysis Group (IMAG), a joint collaboration between LLNL and Sandia National Laboratories/California in biological and materials science research. The 1.7 MV accelerator and an Oxford Microbeams Quadrupole Triplet Lens System are used to create a 3 MeV micron scale ...
Date: September 1, 1997
Creator: Roberts, M.L.; Southon, J.R. & Proctor, I.D.
Partner: UNT Libraries Government Documents Department

The Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory

Description: CAMS operates an HVEC FN tandem accelerator for use in both basic research and technology development. The accelerator is operated under a distributed computer control system with sophisticated auto-scaling, beam flat-topping, archiving, and recall capabilities, which makes possible rapid and precise switching between experimental configurations daily. Using the spectrometer, the AMS group can routinely measure the isotopes {sup 3}H, {sup 9}Be, {sup 10}Be, {sup 14}C, {sup 26}Al, {sup 36}Cl, {sup 41}Ca, and {sup 129}I at abundances as low as 1 part in 10{sup 16}.
Date: October 1, 1996
Creator: Roberts, M.L.; Heikkinen, D.W.; Southon, J.R. & Proctor, I.D.
Partner: UNT Libraries Government Documents Department

{sup 41}Ca as a tracer for calcium uptake and deposition in heart tissue during ischemia and reperfusion

Description: We have developed techniques and are commencing experiments using enriched {sup 41}Ca as a tracer in isolated rabbit heart preparations. The aims of the study are to measure calcium uptake and deposition in response to cardiac ischemia and reperfusion, and to investigate events and mechanism leading to irreversible myocyte injury.
Date: September 17, 1993
Creator: Southon, J. R.; Bishop, M. S. & Kost, G. J.
Partner: UNT Libraries Government Documents Department

Weathering controls on mechanisms of carbon storage in grassland soils

Description: On a sequence of soils developed under similar vegetation, temperature, and precipitation conditions, but with variations in mineralogical properties, we use organic carbon and 14C inventories to examine mineral protection of soil organic carbon. In these soils, 14C data indicate that the creation of slow-cycling carbon can be modeled as occurring through reaction of organic ligands with Al3+ and Fe3+ cations in the upper horizons, followed by sorption to amorphous inorganic Al compounds at depth. Only one of these processes, the chelation of Al3+ and Fe3+ by organic ligands, is linked to large carbon stocks. Organic ligands stabilized by this process traverse the soil column as dissolved organic carbon (both from surface horizons and root exudates). At our moist grassland site, this chelation and transport process is very strongly correlated with the storage and long-term stabilization of soil organic carbon. Our 14C results show that the mechanisms of organic carbon transport and storage at this site follow a classic model previously believed to only be significant in a single soil order (Spodosols), and closely related to the presence of forests. The presence of this process in the grassland Alfisol, Inceptisol, and Mollisol soils of this chronosequence suggests that this process is a more significant control on organic carbon storage than previously thought.
Date: September 1, 2004
Creator: Masiello, C.A.; Chadwick, O.A.; Southon, J.; Torn, M.S. & Harden, J.W.
Partner: UNT Libraries Government Documents Department

Ion-Source Modeling and Improved Performance of the CAMS High-Intensity Cs-Sputter Ion Source

Description: The interior of the high-intensity Cs-sputter source used in routine operations at the Center for Accelerator Mass Spectrometry (CAMS) has been computer modeled using the program NEDLab, with the aim of improving negative ion output. Space charge effects on ion trajectories within the source were modeled through a successive iteration process involving the calculation of ion trajectories through Poisson-equation-determined electric fields, followed by calculation of modified electric fields incorporating the charge distribution from the previously calculated ion trajectories. The program has several additional features that are useful in ion source modeling: (1) averaging of space charge distributions over successive iterations to suppress instabilities, (2) Child's Law modeling of space charge limited ion emission from surfaces, and (3) emission of particular ion groups with a thermal energy distribution and at randomized angles. The results of the modeling effort indicated that significant modification of the interior geometry of the source would double Cs{sup +} ion production from our spherical ionizer and produce a significant increase in negative ion output from the source. The results of the implementation of the new geometry were found to be consistent with the model results.
Date: October 22, 1999
Creator: Brown, T.A.; Roberts, M.L. & Southon, J.R.
Partner: UNT Libraries Government Documents Department

A dedicated AMS (accelerator mass spectrometry) facility for sup 3 H and sup 14 C

Description: Accelerator mass spectrometry is a high sensitivity technique for the detection of numerous long-lived radionuclides at extremely low concentrations. The present use of this measurement tool is primarily in archaeology and the geosciences. However, novel applications and technological advancements that can have a significant impact on both biomedical research and clinical procedures and environmental investigations have been identified. We are studying a small spectrometer for the simultaneous injection and detection of both hydrogen and carbon radioisotopes. 8 refs., 3 figs.
Date: September 1, 1990
Creator: Roberts, M.L.; Southon, J.R.; Davis, J.C.; Proctor, I.D. & Nelson, D.E.
Partner: UNT Libraries Government Documents Department

Radiocarbon dating organic residues at the microgram level

Description: Relation between submilligram sample size and {sup 14}C activity for sample blanks (wood from Pliocene sediments) and a contemporary standard (oxalic acid) for catalytically reduced graphitic carbon was examined down to 20 micrograms. Mean age of the 1 mg wood sample blanks is now about 51.3 ka (0.168 pMC) while the mean for 20 microgram sample blanks is about 42.9 ka. So far, the lowest value for a 1-mg wood sample blank is about 60.5 ka (0.056 pMC). We have determined a mean {sup 14}C age of about 9.4 ka from a suite of 7 organic extracts from hair, bone, and matting from a mummified human skeleton from Spirit Cave, Nevada. These data indicate that the Spirit Cave human is the third, oldest directly-dated, human skeleton currently known from North America.
Date: January 1, 1997
Creator: Kirner, D. L.; Burky, R.; Taylor, R. E. & Southon, J. R.
Partner: UNT Libraries Government Documents Department

14C dating of bone using (gamma) Carboxyglutamic Acid and Carboxyglycine (Aminomalonate)

Description: Radiocarbon determinations have been obtained on {gamma}-carboxyglutamic acid [Gla] and {alpha}-carboxyglycine (aminomalonate) [Am] as well as acid- and base-hydrolyzed total amino acids isolated from a series of fossil bones. As far as they are aware, Am has not been reported previously in fossil bone and neither Gla nor Am {sup 14}C values have been measured previously. Interest in Gla, an amino acid found in the non-collagen proteins osteocalcin and matrix Gla-protein (MGP), proceeds from the suggestion that it may be preferentially retained and more resistant to diagenetic contamination affecting {sup 14}C values in bones exhibiting low and trace amounts of collagen. The data do not support these suggestions. The suite of bones examined showed a general tendency for total amino acid and Gla concentrations to decrease in concert. Even for bones retaining significant amounts of collagen, Gla (and Am extracts) can yield {sup 14}C values discordant with their expected age and with {sup 14}C values obtained on total amino-acid fractions isolated from the same bone sample.
Date: April 27, 1999
Creator: Southon, J R; Burky, R T; Kirner, D L; Taylor, R E & Hare, P E
Partner: UNT Libraries Government Documents Department

Radiocarbon dating of ancient rock paintings

Description: This report presents progress made on a technique for {sup 14}C dating pictographs. A low-temperature oxygen plasma is used coupled with high-vacuum technologies to selectively remove C-containing material in the paints without contamination from inorganic carbon from rock substrates or accretions.
Date: June 20, 1995
Creator: Ilger, W.A.; Hyman, M.; Rowe, M.W. & Southon, J.
Partner: UNT Libraries Government Documents Department

A new 14C calibration data set for the last deglaciation based on marine varves

Description: Varved sediments of the tropical Cariaco basin provide a new {sup 14}C calibration data set for the period of deglaciation (10,000 to 14,500 years before present: 10-14.5 cal ka BP). Independent evaluations of the Cariasco Basin calendar and {sup 14}C chronologies were based on the agreement of varve ages with the GISP2 ice core layer chronology for similar high-resolution paleoclimate records, in addition to {sup 14}C age agreement with terrestrial {sup 14}C dates, even during large climatic changes. These assessments indicate that the Cariaco Basin {sup 14}C reservoir age remained stable throughout the Younger Dryas and late Alleroed climatic events and that the varve and {sup 14}C chronologies provide an accurate alternative to existing calibrations based on coral U/Th dates. The Cariaco Basin calibration generally agrees with coral-derived calibrations but is more continuous and resolves century-scale details of {sup 14}C change not seen in the coral records. {sup 14}C plateaus can be identified at 9.6, 11.4, and 11.7 {sup 14}C ka BP, in addition to a large, sloping plateau during the Younger Dryas ({approximately}10 to 11 {sup 14}C ka BP). Accounting for features such as these is crucial to determining the relative timing and rates of change during abrupt global climate changes of the last deglaciation.
Date: February 22, 1999
Creator: Hughen, K A; Kashgarian, M; Lehman, S J; Overpeck, J T; Peterson, L C & Southon, J R
Partner: UNT Libraries Government Documents Department

Low-Charge State AMS for High Throughput 14C Quantification

Description: Accelerator mass spectrometry (AMS) quantifies attomole (10{sup -18}) amounts of {sup 14}C in milligram sized samples. This sensitivity is used to trace nutrients, toxins and therapeutics in humans and animals at less than {micro}g/kg doses containing 1-100 nCi of {sup 14}C. Widespread use of AMS in pharmaceutical development and biochemical science has been hampered by the size and expense of the typical spectrometer that has been developed for high precision radiocarbon dating. The precision of AMS can be relaxed for biochemical tracing, but sensitivity, accuracy and throughput are important properties that must be maintained in spectrometers designed for routine quantification. We are completing installation of a spectrometer that will maintain the high throughput of our primary spectrometer but which requires less than 20% of the floor space and of the cost. Sensitivity and throughput are kept high by using the LLNL intense cesium sputter ion source with solid graphitic samples. Resultant space-charge effects are minimized by careful modeling to find optimal ion transport in the spectrometer. A long charge-changing ''stripper gas'' volume removes molecular isobars at potentials of a few hundred kiloVolts, reducing the size of the accelerating component. Fast ion detectors count at high rates to keep a wide dynamic range for 14 C concentrations. Solid sample presentation eliminates the sample cross contamination that degrades accuracy and the effects of ''memory'' in the ion source. Automated processes are under development for conversion of liquid and solid biological samples to the preferred graphitic form for the ion source.
Date: June 16, 2000
Creator: Ognibene, T. J.; Roberts, M. L.; Southon, J. R. & Vogel, J. S.
Partner: UNT Libraries Government Documents Department

PXAMS -- Projectile X ray AMS: X ray yields and applications

Description: Characteristic x rays have recently been explored as a method for the detection and identification of ions in accelerator mass spectrometry (AMS). After analysis in the AMS spectrometer, the ions stop in an appropriately chosen target and the induced x rays identify the ions by atomic number. For the application of AMS to higher mass isotopes, characteristic x rays allow significantly better discrimination of competing atomic isobars than is possible using energy loss detectors. Characteristic x rays also show promise as a convenient component in hybrid detection systems. Measurements of x ray yields are presented for Si, Fe, Ni, Se, Mo, and Pd ions of 0.5--2 MeV/AMU. The yields rise by more than a factor of 10 over this energy range, and approach 1 x-ray per incident ion at 2 MeV/AMU for the lighter ions. Preliminary work on the application of PXAMS to the detection of {sup 79}Se is described.
Date: October 7, 1994
Creator: McAninch, J. E.; Bench, G. S.; Freeman, S. P. H. T.; Roberts, M. L.; Southon, J. R.; Vogel, J. S. et al.
Partner: UNT Libraries Government Documents Department

Plutonium measurements by accelerator mass spectrometry at LLNL

Description: Mass spectrometric methods provide sensitive, routine, and cost-effective analyses of long-lived radionuclides. Here the authors report on the status of work at Lawrence Livermore National Laboratory (LLNL) to develop a capability for actinide measurements by accelerator mass spectrometry (AMS) to take advantage of the high potential of AMS for rejection of interferences. This work demonstrates that the LLNL AMS spectrometer is well-suited for providing high sensitivity, robust, high throughput measurements of plutonium concentrations and isotope ratios. Present backgrounds are {approximately}2 x 10{sup 7}atoms per sample for environmental samples prepared using standard alpha spectrometry protocols. Recent measurements of {sup 239+240}Pu and {sup 241}Pu activities and {sup 240}Pu/{sup 239}Pu isotope ratios in IAEA reference materials agree well with IAEA reference values and with alpha spectrometry and recently published ICP-MS results. Ongoing upgrades of the AMS spectrometer are expected to reduce backgrounds below 1 x 10{sup 6} atoms per sample while allowing simplifications of the sample preparation chemistry. These simplifications will lead to lower per-sample costs, higher throughput, faster turn around and, ultimately, to larger and more robust data sets.
Date: October 26, 1999
Creator: McAninch, J E; Hamilton, T F; Broan, T A; Jokela, T A; Knezovich, T J; Ognibene, T J et al.
Partner: UNT Libraries Government Documents Department

Progress in AMS measurements at the LLNL spectrometer. [Accelerator Mass Spectroscopy (AMS)]

Description: The AMS measurement program at LLNL began in earnest in late 1989, and has initially concentrated on {sup 14}C measurements for biomedical and geoscience applications. We have now begun measurements on {sup 10}Be and {sup 36}Cl, are presently testing the spectrometer performance for {sup 26}Al and {sup 3}H, and will begin tests on {sup 7}Be, {sup 41}Ca and {sup 129}I within the next few months. Our laboratory has a strong biomedical AMS program of {sup 14}C tracer measurements involving large numbers of samples (sometimes hundreds in a single experiment) at {sup 14}C concentrations which are typically .5--5 times Modern, but are occasionally highly enriched. The sample preparation techniques required for high throughput and low cross-contamination for this work are discussed elsewhere. Similar demands are placed on the AMS measurement system, and in particular on the ion source. Modifications to our GIC 846 ion source, described below, allow us to run biomedical and geoscience or archaeological samples in the same source wheel with no adverse effects. The source has a capacity for 60 samples (about 45 unknown) in a single wheel and provides currents of 30--60{mu}A of C{sup {minus}} from hydrogen-reduced graphite. These currents and sample capacity provide high throughput for both biomedical and other measurements: the AMS system can be started up, tuned, and a wheel of carbon samples measured to 1--1.5% in under a day; and 2 biomedical wheels can be measured per day without difficulty. We report on the present status of the Lawrence Livermore AMS spectrometer, including sample throughput and progress towards routine 1% measurement capability for {sup 14}C, first results on other isotopes, and experience with a multi-sample high intensity ion source. 5 refs.
Date: June 1, 1991
Creator: Southon, J.R.; Vogel, J.S.; Trumbore, S.E.; Davis, J.C.; Roberts, M.L.; Caffee, M. et al.
Partner: UNT Libraries Government Documents Department

Biological sample preparation and {sup 41}Ca AMS measurement at LLNL

Description: Calcium metabolism in biology may be better understood by the use of {sup 41}Ca labels, although detection by accelerator mass spectrometry (AMS) is required. Methodologies for preparation of urine samples and subsequent AMS measurement were investigated. Novel attempts at preparing CaH{sub 2} were unsuccessful, but CaF{sub 2} of sufficient purity could be produced by precipitation of calcium from urine as oxalate, followed by separation of calcium by cation exchange chromatography and washing the CaF{sub 2} precipitate. The presence of some remaining impurities could be compensated for by selecting the appropriate accelerated ion charge state for AMS. The use of projectile x rays for isobar discrimination was explored as an alternative to the conventional dE/dx device.
Date: October 10, 1994
Creator: Freeman, S. P. H. T.; Southon, J. R.; Bench, G. S.; McAninch, J. E.; Serfass, R. E.; Fang, Y. et al.
Partner: UNT Libraries Government Documents Department

Comment on "Radiocarbon Calibration Curve Spanning 0 to 50,000 Years B.P. Based on Paired 230Th/234U/238U and 14C Dates on Pristine Corals" by R.G. Fairbanks, R. A. Mortlock, T.-C. Chiu, L. Cao, A. Kaplan, T. P. Guilderson, T. W. Fairbanks, A. L. Bloom, P

Description: Radiocarbon calibration curves are essential for converting radiocarbon dated chronologies to the calendar timescale. Prior to the 1980's numerous differently derived calibration curves based on radiocarbon ages of known age material were in use, resulting in ''apples and oranges'' comparisons between various records (Klein et al., 1982), further complicated by until then unappreciated inter-laboratory variations (International Study Group, 1982). The solution was to produce an internationally-agreed calibration curve based on carefully screened data with updates at 4-6 year intervals (Klein et al., 1982; Stuiver and Reimer, 1986; Stuiver and Reimer, 1993; Stuiver et al., 1998). The IntCal working group has continued this tradition with the active participation of researchers who produced the records that were considered for incorporation into the current, internationally-ratified calibration curves, IntCal04, SHCal04, and Marine04, for Northern Hemisphere terrestrial, Southern Hemisphere terrestrial, and marine samples, respectively (Reimer et al., 2004; Hughen et al., 2004; McCormac et al., 2004). Fairbanks et al. (2005), accompanied by a more technical paper, Chiu et al. (2005), and an introductory comment, Adkins (2005), recently published a ''calibration curve spanning 0-50,000 years''. Fairbanks et al. (2005) and Chiu et al. (2005) have made a significant contribution to the database on which the IntCal04 and Marine04 calibration curves are based. These authors have now taken the further step to derive their own radiocarbon calibration extending to 50,000 cal BP, which they claim is superior to that generated by the IntCal working group. In their papers, these authors are strongly critical of the IntCal calibration efforts for what they claim to be inadequate screening and sample pretreatment methods. While these criticisms may ultimately be helpful in identifying a better set of protocols, we feel that there are also several erroneous and misleading statements made by these authors which require a response by the IntCal working ...
Date: October 2, 2005
Creator: Reimer, P J; Baillie, M L; Bard, E; Beck, J W; Blackwell, P G; Buck, C E et al.
Partner: UNT Libraries Government Documents Department