P. A. Hausladen

Analysis of plutonium isotopes in marine samples by radiometric, ICP-MS and AMS techniques

IAEA reference materials (radionuclides in the marine environment) collected in areas affected by nuclear reprocessing plants and nuclear weapons tests have been analysed by semiconductor alpha-spectrometry (SAS), liquid scintillation spectrometry (LSS) and mass spectrometric techniques (high resolution ICP-MS and AMS) with the aim of developing analytical procedures and to study the geochemical behavior of plutonium in the marine environment. The Pu results obtained by SAS, ICP-MS and AMS were in reasonably good agreement (R2 = 0.99). The mean atom ratios of 240Pu/239Pu in IAEA reference materials, IAEA-134, 135 and 381 were (0.212±0.010), (0.211±0.004) and (0.242±0.004), respectively. IAEA-384 (Fangataufa Lagoon Sediment) gave a 240Pu/239Pu mean atom ratio of 0.051±0.001. The results of 241Pu obtained by ICP-MS and LSS also show reasonable agreement (R2 = 0.91). Pu isotopic signatures were useful in tracing Pu origin and in interpreting biogeochemical processes involving Pu in the marine environment.

Radiocarbon dating of the human occupation of Australia prior to 40 ka BP; successes and pitfalls.

Charcoal samples from ancient human occupation sites in Australia have been subjected to a rigorous pretreatment and stepped combustion regime in order to explore the possibility that these sites may be older than previous radiocarbon dating had suggested. In one case, the Devils Lair site in southwest Australia, the methodology has clearly removed vestiges of contamination by more modern carbon and has led to a revised radiocarbon chronology that provides evidence for human occupation of southwest Australia by at least 44 ka BP and probably by 46-47 ka BP. In contrast, charcoal from the Nauwalabila site has been so severely altered that insufficient of the original carbon remains for reliable (super 14) C dating. Finally, where the charcoal is well preserved, such as at the Carpenters Gap site, the new results provide reassurance that earlier (super 14) C results of approximately 40 ka BP are indeed true ages and are not simply at the limit of the (super 14) C technique.

Chronology of the atmospheric mercury in Lagoa da Pata Basin, Upper Rio Negro region of Brazilian Amazon

We present prehistoric mercury accumulation rates in a dated sediment core from Lagoa da Pata, a remote lake in Sao Gabriel da Cachoeira, northern Amazon. The sediment samples were subdivided for mercury and radiocarbon analyses. A group of 18 samples have been prepared at ANU for (super 14) C dating by accelerator mass spectrometry (AMS). The dating results show a good correlation with depth in the core, down to 41,500 BP. Three distinct sections are clearly identified in the core. They consist of upper and lower organic-rich layer, separated by an inorganic layer which represents a short period of rapid accumulation around 18 ka BP. The mercury accumulation rate is found to be larger in the upper layer (18 ka to present) than in the lower one (41 ka to 25 ka), by a factor of three. The larger accumulation rate of mercury is probably associated with warmer temperatures and a higher frequency of forest fires during the Holocene.

Accelerator mass spectrometry of 99Tc

Abstract The measurement of low levels of 99Tc (T 1/2 =213 ka ) by accelerator mass spectrometry (AMS) is reported for the first time. Because there are no stable isotopes of technetium, the 99Tc content of a sample is determined from the ratio of 99Tc to a known trace amount of 103Rh. High-purity aluminium oxide constitutes the bulk of each sample. The contribution from the 99Ru isobar may be quantified and subtracted using 101Ru. In contrast to conventional AMS in which at least one isotope is measured as a beam current, here all three isotopes, 99Tc, 101Ru and 103Rh, are counted ion-by-ion in a propane-filled ionization chamber. This ionization chamber permits partial, but not complete, separation of 99Tc from 99Ru ions. The technique has been validated using a series of standards, as well as a set of five seaweed samples from an inter-laboratory comparison exercise. In addition, the technique has been used to measure the relative intensities of the Tc− and TcOm− (m=1–4) negative ions from a Cs sputter ion source.

Simple concepts for ion source improvement

Abstract We report on improvements in the overall intensity of a sputter ion source that evolved originally from an NEC MCSNICS. Beam output increases benefit both AMS measurements and nuclear physics experiments using low natural abundance beams. In particular, minor changes in source geometry suggested by a combination of electrostatic calculations and simple design principles have yielded increases in extracted negative ion intensity of nearly a factor of 4.