ENVIRONMENTAL APPLICATIONS OF THE LANL NUCLEAR MICROPROBE

The LANL nuclear microprobe has been used to study the distributions o f trace elements (TE) of environmental interest including: (1) metals in coal and fly ash, (2) Pb in the Bandelier Tuff (BT), (3) Ba in tree rings, (4) Mn, Fe, Sr and Y in Yucca Mountain calcites. These studies illustrate environmental problems that can be addressed using nuclear microprobes. Micro-PIXE (MP) analyses with 5-10 micrometer spatial re solution provide constraints on processes that redistribute contaminan ts in the environment, and hence may help answer environmental problem s where fine-scale chemical records are important. MP analyses of part iculates in coal and ash show that pyrite contains As, Se, Hg and Pb; macerals contain Cr, halogens and S; cenospheres contain As, Se and Ni ; and hematite ash contains Ni and As. Understanding these elemental m odes of occurrence allows prediction of metal behavior in boilers and may enhance compliance with the Clean Air Act Amendments. Fine-grained high-Pb minerals were identified using SEM and MP analyses of BT mine rals. These minerals were from samples associated with deep-groundwate r wells containing Pb at levels greater than regulatory limits. Pb is concentrated in Pb minerals (e.g. cerussite), smectite, and hematite f ormed during low-T alteration of tuff. Understanding mineralogic speci ation of metals may provide insights into sources of groundwater pollu tion. Tree rings from ponderosa pines that grew in a Ba-contaminated d rainage were analyzed using MP. Ba concentrations are typically higher in rings that formed after operations discharging Ba to the environme nt began. Such tree-ring analyses may ultimately provide information o n rates of contaminant migration in the environment. TE in zoned calci tes from Yucca Mountain were analyzed by MP. Calcites from the saturat ed zone (SZ) have distinct chemical signatures (high Fe, Mn and low Y) . No calcites in the unsaturated zone with SZ chemical signatures were found using MP. MP analyses of vein minerals can provide insights int o mineral sources and hydrogeologic processes. These examples show tha t TE microanalysis with nuclear microprobes can provide insights into a wide variety of environmental processes. Such information allows mor e informed, technically defensible negotiations with regulators, savin g time and money in environmental cleanup projects. (C) 1997 Elsevier Science B.V.