No abstract

We have compared the transport behavior in various environments of radionuclides originating from underground nuclear tests at the Nevada Test Site (NTS). Under saturated conditions in both alluvium and fractured volcanic rock, 36 C1, 129 I, and 3 H exhibit mutually consistent and presumably conservative behavior during saturated flow. At the saturated fractured rock site, "Tc was conservative under most conditions, but was not present in samples containing high levels of iron oxyhydroxides formed in the well water. 125 Sband 137 Cs transport was observed in fracture flow, but concentrations of Sb were somewhat attenuated and Cs was strongly retarded. Total activity levels of these nonconservative nuclides were not affected by the particulate phenomena that reduced "Tc levels. Studies of transport in unsaturated alluvium showed that neither 36 C1 nor 129 I were conservative relative to tritium. Observations of the relative transport behavior of the radionuclides as functions of both time and distance permit deductions about the nature of their source terms.

A coiled fiber-optic chemical sensor has proven to be effective for the remote detection of volatile organic compounds, such as trichloroethylene (TCE), 1,1-dichloroethylene (DCE), and gasoline, in aqueous solutions. The analyte diffuses into the hydrophobic cladding and evanescent wave absorption spectra are measured in the near-infrared (1600–1850 nm) without the presence of the water absorption bands. In order for fiberoptic chemical sensors to operate effectively in remote environments, the influence of temperature on the sensor response must be known. The C-H bonds of the polysiloxane cladding material also have absorption bands in the near-infrared (NIR). Changes in temperature will change the density (i.e., concentration of C-H bonds) and refractive index of the cladding. Due to these effects, a temperature change of only 3°C from the reference has been shown to significantly alter the background absorbance. The temperature-dependent background absorption is found to be linear with the slope, and the values are proportional to the absorption coefficient of the cladding material. The intercept of the absorbance vs. temperature plot is found to follow the first derivative of the fiber sensor transmission spectrum. Evanescent wave absorption spectra of TCE solutions have been corrected for temperature.