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Physicochemical basis of the Na-K-Ca geothermometer

Description: Regular changes in solution composition were observed experimentally during granite reaction with dilute NaCl (+CaCl/sub 2/) solutions; these changes closely follow the empirical Na-K-Ca geothermometer relationship. Initial minerals forming the granite (quartz, plagioclase, K-feldspar, and biotite) were etched by the reactions. Alteration phases formed include calcium-zeolite at <300/sup 0/C, feldspar overgrowths at >300/sup 0/C, and minor amounts of clay and calcsilicate at all temperatures. Amphibole overgrowths were also found at 340/sup 0/C. Quartz is near saturation in all experiments, and preliminary calculations of aqueous species distributions and mineral affinities indicate that the solutions achieve super-saturation with feldspars as the temperature increase. A consistent variation attributable to pH differences was observed in the empirical geothermometer relationship for all experimental data. At 340/sup 0/C, the experimental solutions appear to have deviated slightly from the empirical Na-K-Ca relationship. Such deviations may also be found in natural systems that attain such temperatures.
Date: August 1, 1986
Creator: Janecky, D.R.; Charles, R.W.; Bayhurst, G.K. & Benjamin, T.M.
Partner: UNT Libraries Government Documents Department

Microscopic distribution of trace elements in minerals (chlorites, sulfides, sulfates) in submarine hydrothermal systems

Description: We have analyzed trace elements in two types of hydrothermal precipitates using the Los Alamos Nuclear Microprobe. Chlorites and epidotes in basalt were analyzed from the Samail Ophiolite of Oman. Sulfide and sulfate minerals were analyzed from samples of active chimney walls from 21/degree/N. East Pacific Rise. These samples are ideal for our study because of the extensive background information available on processes and component characteristics. Initial results indicate significant differences in mobile trace elements between chlorites associated with and those distinctly separate from major stockwork flow zones, consistent with greater water-rock reaction within stockworks. Trace element concentrations across chimney walls also exhibit distinctive patterns which can be correlated with mineral/chemical zonation and possible also with variations in elemental source. 9 refs., 2 figs., 1 tab.
Date: January 1, 1989
Creator: Janecky, D.R.; Benjamin, T.M.; Rogers, P.S.Z.; Bayhurst, G.K. & Haymon, R.M.
Partner: UNT Libraries Government Documents Department

Plutonium and Uranium Atom Ratios and Activity Levels in Cochiti Lake Bottom Sediments Provided by Pueblo de Cochiti

Description: Historical operations at the Los Alamos National Laboratory have contaminated stream sediments with plutonium and other radionuclides. A small portion of these contaminated sediments has been carried by floods into the Rio Grande drainage system, eventually to be trapped by Cochiti Lake located on Pueblo de Cochiti lands approximately 8 km downstream of the Laboratory. In this study, lake bottom sediment samples provided by the Pueblo de Cochiti were analyzed by thermal ionization mass spectrometry to determine plutonium and uranium activity levels and isotopic atom ratios. This specialized analytical method allows us to take isotopic fingerprints of radionuclides found in the sediment and to determine how much plutonium and uranium came from the Laboratory and how much was deposited by worldwide fallout or is natural. Two distinct types of samples were processed: segments of a continuous vertical core of the entire accumulated sediment sequence and other samples from across the lake bottom at the water/sediment interface. Based on measurement of the {sup 240}Pu/{sup 239}Pu atom ratio, Laboratory-derived plutonium is present in eight of nine samples at the core site. On a depth-weighted basis, approximately one-half of the {sup 239}Pu and {sup 240}Pu came from early operations at the Laboratory; the remaining plutonium came from fallout dispersed by above-ground nuclear tests. In contrast to the core site, the samples from the other locations showed little or no evidence of Laboratory-derived plutonium, with more than 90 percent of the plutonium attributable to fallout. The overall amount of plutonium in all the samples is of the same magnitude as other reservoirs in the region. The net increase in plutonium over upstream reservoirs unaffected by Laboratory activities is a maximum of 0.014 pCi/g or 3.5 times. All of the samples reflect natural uranium compositions. Laboratory-derived uranium is not identifiable, presumably because the sediment contains ...
Date: May 1, 1999
Creator: Gallaher, B.M.; Efurd, D.W.; Rokop, D.J. & Benjamin, T.M.
Partner: UNT Libraries Government Documents Department

Development and application of the Los Alamos nuclear microprobe: hardware, software, and calibration

Description: There is a great demand for spatially resolved quantitative trace element analyses of geologic samples. This class of samples is characteristically heterogeneous, fine grained, and compositionally complex. The Los Alamos nuclear microprobe has been developed for, and applied to, non-destructive in-situ geochemical analysis, primarily using the proton induced x-ray emission technique (PIXE). Characteristic x-ray spectra are acquired by bombardment with 1 to 200 nA beams of protons from the Los Alamos vertical Van de Graaff accelerator. Beam spot diameters of 10 ..mu..m are routine. After spectrum deconvolution, detection limits of approximately 5 ppM are obtained for an integrated charge on the order of 10 ..mu..C. Applications, concomitant with development have included analyses of meteorites, including one potential sample of Mars, terrestrial oil shales, archaeological artifacts, and ore mineral samples.
Date: January 1, 1985
Creator: Benjamin, T.M.; Rogers, P.S.Z.; Duffy, C.J.; Conner, J.F.; Maggiore, C.J. & Tesmer, J.R.
Partner: UNT Libraries Government Documents Department

Microprobe analyses of rare-earth-element fractionation in meteoritic minerals

Description: Two meteorites were analyzed by PIXE with the Los Alamos Nuclear Microprobe. The enstatite achondrite Pena Blanca Spring and the ordinary chondrite St. Severin were chosen as likely candidates for use in /sup 244/Pu (t/sub 1/2/ = 82 my) cosmochronology and geochronology. These applications require the meteoritic minerals to have unfractionated actinides and lanthanides relative to cosmic elemental abundance ratios. The PIXE analyses produced evidence of actinide-lanthanide fractionation in Pena Blanca Spring oldhamite (CaS) whereas the St Severin phosphates, whitlockite and chlorapatite, do not exhibit this fractionation.
Date: January 1, 1983
Creator: Benjamin, T.M.; Duffy, C.J.; Rogers, P.S.Z.; Maggiore, C.J.; Woolum, D.S.; Burnett, D.S. et al.
Partner: UNT Libraries Government Documents Department

Survey of plutonium and uranium atom ratios and activity levels in Mortandad Canyon

Description: For more than three decades, Mortandad Canyon has been the primary release area of treated liquid radioactive waste from the Los Alamos National Laboratory (Laboratory). In this survey, six water samples and seven stream sediment samples collected in Mortandad Canyon were analyzed by thermal ionization mass spectrometry to determine the plutonium and uranium activity levels and atom ratios. By measuring the {sup 240}Pu/{sup 239}Pu atom ratios, the Laboratory plutonium component was evaluated relative to that from global fallout. Measurements of the relative abundance of {sup 235}U and {sup 236}U were also used to identify non-natural components. The survey results indicate that the Laboratory plutonium and uranium concentrations in waters and sediments decrease relatively rapidly with distance downstream from the major industrial sources. Plutonium concentrations in shallow alluvial groundwater decrease by approximately 1,000-fold along a 3,000-ft distance. At the Laboratory downstream boundary, total plutonium and uranium concentrations were generally within regional background ranges previously reported. Laboratory-derived plutonium is readily distinguished from global fallout in on-site waters and sediments. The isotopic ratio data indicate off-site migration of trace levels of Laboratory plutonium in stream sediments to distances approximately two miles downstream of the Laboratory boundary.
Date: October 1, 1997
Creator: Gallaher, B.M.; Efurd, D.W.; Rokop, D.J.; Benjamin, T.M. & Stoker, A.K.
Partner: UNT Libraries Government Documents Department

Survey of plutonium and uranium atom ratios and activity levels in Mortandad Canyon

Description: For more than three decades Mortandad Canyon has been the primary release area of treated liquid radioactive waste from the Los Alamos National Laboratory (Laboratory). In this survey, six water samples and seven stream sediment samples collected in Mortandad Canyon were analyzed by thermal ionization mass spectrometry (TIMS) to determine the plutonium and uranium activity levels and atom ratios. Be measuring the {sup 240}Pu/{sup 239}Pu atom ratios, the Laboratory plutonium component was evaluated relative to that from global fallout. Measurements of the relative abundance of {sup 235}U and {sup 236}U were also used to identify non-natural components. The survey results indicate the Laboratory plutonium and uranium concentrations in waters and sediments decrease relatively rapidly with distance downstream from the major industrial sources. Plutonium concentrations in shallow alluvial groundwater decrease by approximately 1000 fold along a 3000 ft distance. At the Laboratory downstream boundary, total plutonium and uranium concentrations were generally within regional background ranges previously reported. Laboratory derived plutonium is readily distinguished from global fallout in on-site waters and sediments. The isotopic ratio data indicates off-site migration of trace levels of Laboratory plutonium in stream sediments to distances approximately two miles downstream of the Laboratory boundary.
Date: September 22, 1997
Creator: Gallaher, B.M.; Benjamin, T.M.; Rokop, D.J. & Stoker, A.K.
Partner: UNT Libraries Government Documents Department

Isotopic signatures: An important tool in today`s world

Description: High-sensitivity/high-accuracy actinide measurement techniques developed to support weapons diagnostic capabilities at the Los Alamos National Laboratory are now being used for environmental monitoring. The measurement techniques used are Thermal Ionization Mass Spectrometry (TIMS), Alpha Spectrometry(AS), and High Resolution Gamma Spectrometry(HRGS). These techniques are used to address a wide variety of actinide inventory issues: Environmental surveillance, site characterizations, food chain member determination, sedimentary records of activities, and treaty compliance concerns. As little as 10 femtograms of plutonium can be detected in samples and isotopic signatures determined on samples containing sub-100 femtogram amounts. Uranium, present in all environmental samples, can generally yield isotopic signatures of anthropogenic origin when present at the 40 picogam/gram level. Solid samples (soils, sediments, fauna, and tissue) can range from a few particles to several kilograms in size. Water samples can range from a few milliliters to as much as 200 liters.
Date: December 1, 1995
Creator: Rokop, D.J.; Efurd, D.W.; Benjamin, T.M.; Cappis, J.H.; Chamberlin, J.W.; Poths, H. et al.
Partner: UNT Libraries Government Documents Department