A simple, yet highly reproducible separation procedure for isolating low levels of protactinium /pico- to micrograms/ from gram quantities of natural or activated soils or sediments has been developed. The reliability is achieved by minimizing the tendency of Pa to hydrolyze or to form colloids by keeping it complexed at all times either by fluoride or sulfate ions. The procedure consistently gives high chemical yields /85+8%/ and the final fractions are not only radiochemically pure, but show little or no visible mass contamination with evaporation.
Oceanographers use the cosmogenic radionuclide 7Be (T1/2 53 days) as a tracer for atmospheric input and a conservative tracer of mixing in the open ocean. This paper elucidates a
method for improving the analysis of 7Be from seawater. The scavenging efficiency of Fe(OH)3 for each sample is measured by ICP-MS using stable 9Be as a yield monitor. Samples are gamma-counted in a large diameter (28 mm) well detector. The high purity germanium well
detector is coupled with an active anti-coincidence cosmic guard to reduce the spectra background. The improved overall accuracy
of the method and lower detection limit of the detector results in a lower volume of seawater needed for analyses. Results
will be shown from a study of 7Be in the Sargasso Sea.
Authors:S. M. Pike, K. O. Buesseler, J. Andrews, and N. Savoye
Development of a small volume (2-4 liter) technique for measuring 234 Th in sea water has been instrumental in bringing to light small-scale structures in upper-ocean particle removal processes previously missed by standard 234 Th measurement techniques. Further development of this method to evaluate removal efficiencies of 234 Th via MnO2 precipitation quantified using ICP-MS are presented in this work. Advantages to this approach are precise knowledge of 234 Th recovery, while maintaining high sample throughput afforded by ICP-MS analyzes. The improved technique includes the acidification of 4-liter sea water samples and the addition of 230 Th as a yield monitor prior to MnO2 precipitation. Subsequent filtration and beta-counting of the high-energy daughter, 234mPa, was followed by a final background count after 6 half-lives (144 d) of decay. Filtered precipitates were dissolved with H2O2, and an internal standard of 229 Th was added. Samples were purified using anion-exchange chromatography to remove high levels of manganese, and recoveries were determined by measured ratios of 230 Th/229 Th by ICP-MS. Application of this procedure for 234 Th derived export in the recent Southern Ocean Iron Experiment showed average recoveries of 91%. Corrections for rare low recoveries (25-80%) noticeably change 234 Th profiles, thus impacting subsequent elemental flux calculations.
Authors:G. Klunder, J. Andrews, M. Church, J. Spear, R. Russo, P. Grant, and B. Andresen
Capillary electrophoresis has been used to separate metal ions characteristically associated with nuclear fission. Electrokinetic
injections and transient isotachophoretic techniques were employed to increase sample loading and provide on-column concentration
of the analyte. On-line concentration factors of approximately 700-fold have been achieved. Indirect-UV absorbance, on-line
radioactivity, and indirect laser-induced fluorescence detection were used to monitor analytes of interest. The radioactivity
detector consists of a plastic scintillator and photomultiplier tube with a 4π detection geometry. The efficiency was determined
to be approximately 80%, enabling samples resident in the detector window for 0.1 minutes to be reliably assayed. Detection
of152Eu and137Cs was achieved at the low nCi level. Indirect fluorescence was performed with quinine sulfate as the background fluorophor
with α-hydroxysobutyric acid added as a complexing agent. An argon ion laser was used as the excitation source with a diode
array detector. Limits of detection for La3+, Ce3+, Pr3+, Nd3+, Sm3+, and Eu3+ were determined to be in the sub — 10 ppb range (6–11 nM) with indirect laser-induced fluorescence detection.
Authors:D. J. Sims, W. S. Andrews, K. A. M. Creber, and X. Wang
In 1951, 6.7 liters of an aqueous acidic solution of irradiated uranium (360 GBq) leaked from a buried storage tank into unsaturated prairie soil, where it has remained, undisturbed. In October 2001, sonic drilling was conducted to recover core samples around and below the tank location. This paper describes the measurements and investigative approaches being pursued to determine the transport properties of the various fission and daughter products and actinides. Separate effects laboratory experiments are also being conducted involving both inert and radioactive samples in similar soil, to examine the effects on transport properties (diffusion and sorption) of temperature, recharge and discharge rates, concentration and soil porosity. Finally, transport modeling approaches are discussed.
Authors:C. Benitez-Nelson, K. Buesseler, M. van der Loeff, J. Andrews, L. Ball, G. Crossin, and M. Charette
Thorium-234 is a naturally occurring radionuclide that has been widely studied in ocean sciences. These studies use the disequilibrium between the soluble parent uranium-238 (T1/2 = 4.5·109 y), and its particle reactive daughter, 234Th (T1/2 = 24.1 d), to quantify the in-situ removal rates of 234Th on sinking particles. Here, we present additional experiments that test a new 2-l procedure in which 234Th is co-scavenged with a MnO2 precipitate. Unlike other techniques, this method can be easily applied at-sea with an overall precision and accuracy of 5%. Our experiments have sought to elucidate the effects of delaying reagent addition and precipitate filtration, differences in sample bottle types, and issues related to sample backgrounds and 234Th particulate sampling. Most of these experiments were conducted using water collected on repeated occupations of station ALOHA (22°45.0'N, 158°00.0'W), 100 km North of Oahu, Hawaii.
Authors:P. Grant, K. Moody, I. Hutcheon, D. Phinney, R. Whipple, J. Haas, A. Alcaraz, J. Andrews, G. Klunder, R. Russo, T. Fickies, G. Pelkey, B. Andresen, D. Kruchten, and S. Cantlin
Over the past several years, the Livermore Forensic Science Center has conducted analyses of nuclear-related samples in conjunction
with domestic and international criminal investigations. Law enforcement officials have sought conventional and nuclear-forensic
analyses of questioned specimens that have typically consisted of miscellaneous metal species or actinide salts. The investigated
activities have included nuclear smuggling and the proliferation of alleged fissionable materials, nonradioactive hoaxes such
as “Red Mercury,” and the interdiction of illegal laboratories engaged in methamphetamine synthesis.