Gregory M. Nau

Multivariate Analysis of Mid-IR FT-IR Spectra of Hydrocarbon-Contaminated Wet Soils

This article describes a series of mid-IR FT-IR reflectance spectroscopy measurements of hydrocarbon-contaminated wet soils. The eventual goal of this work is the development of an analysis tool suitable for real-time in situ underground measurements where a suitable reference spectrum is not available. Multivariate analysis of the resulting spectral data indicates that the strongly varying wet soil matrix and the absence of a suitable reference spectrum in the field do not render this measurement technique unfeasible as a means of realizing remote in situ chemical detection in wet soils. It was also observed that simultaneous quantification of moisture content and identification of soil composition may be achieved. These results have important applications to in situ site characterization for environmental cleanup and soil characterization for construction planning.

Fiber-optic near-infrared reflectance sensor for detection of organics in soils

A near infrared fiber-optic chemical sensor system using reflectance spectroscopic measurements has been assembled. This system was evaluated and found attractive for remote detection of organics in soils over distances of at least 30 meters.<<ETX>>

Fiber optic IR reflectance sensor for the cone penetrometer

A compact, ruggedized fiber optic IR reflectance probe for remote, in-situ screening of underground waste sites has been developed. Using cabled chalcogenide optical fibers and a FTIR system, remote spectroscopy has been performed over distances of 20 meters. This paper discusses the design and performance of this system.

Remote Detection of Trichloroethylene in Soil by a Fiber-Optic Infrared Reflectance Probe

A remote detection method for measuring the infrared reflectance from chlorinated hydrocarbons in soils is demonstrated. The method uses a 12-m-long, field-ruggedized, chalcogenide fiber to transmit IR reflectance data to a remotely located FT-IR spectrometer. Minimum observable signal corresponding to 250 ppm of trichloroethylene (TCE) in sand was measured with the system. Suggestions for improving the threshold detection limit are offered.

Fiber optic infrared reflectance probe for detection of hydrocarbon fuels in soil

The acquisition of fiber optic reflectance spectra of diesel fuel marine (DFM) dispersed on sea sand is described. Reflectance spectra are acquired by collection of the diffusely scattered light from a black body source imaged onto a specially designed sample cell. Samples of DFM were prepared by diluting a stock standard containing 10 wt% DFM on sea sand. Interactive band analysis is used to remove the background absorption due to residual water on the sand. Results indicate a linear relationship between the band depth at 3.68 microns and the concentration of DFM. Statistical analysis of ten replicate measurements of a 0.02 wt% DFM on sea sand gives the average band depth and 95% confidence interval of 0.02875 +/- 0.000654. An instrumental detection limit of 0.0033 percent reflectance is calculated from the standard deviation of the replicate measurements.

Effect of ionizing radiation on in situ Raman scattering and photoluminescence of silica optical fibers

Raman fiber optic chemical sensors provide remote in situ characterization capability. One application of Raman fiber optic chemical sensors is the characterization of the contents of nuclear waste tanks. In these tanks it is expected that approximately 20 meters of optical fiber will be exposed to radiation levels between 100 and 1000 rads/hour. In support of this work two silica optical fiber types (one a communications grade fiber and the other nominally radiation resistant) have been tested at the radiation levels expected in the tanks. Luminescence and Raman scattering measurements have been performed in situ with 488-nm excitation on two types of silica optical fiber exposed to a constant low to moderate dose rate of gamma radiation of 880 rads(Si)/hour from a /sup 60/Co source for a total dose of greater than 45 krads. The nominally radiation-resistant fiber was also excited with 514.5-nm and near-infrared 830-nm laser radiation. The rate of the silica Raman signal decrease is more than three times greater for the visible excitation wavelengths than for the 830-nm excitation for the radiation resistant fiber. The behavior of the 650-nm photoluminescence line upon irradiation was different for the two fibers studied, both in terms of the shift of the 650-nm line and rate of increase of the normalized photoluminescence intensity. In all cases the photoluminescence from the fibers was less than the Raman intensity. No radioluminescence was observed in either fiber. The radiation resistant fiber exhibited photobleaching effects on the Raman transmission when photoannealed with 488-nm laser light. >

Detection of trace levels of mercury in aqueous systems via a fiber optic probe

Currently there is a great deal of interest in the development and use of fiber optic chemical sensors for characterization of contaminated waste sites. Development of remote, in-situ sensors for rapid determination of the presence, and concentration of hazardous materials will significantly reduce site remediation costs. The state-of-the-art technology for assessing site contamination is the cone penetrometer system. This system consists of a 2-1/2 ton truck, a hydraulic ram, and a steel tube. The steel tube, which is generally 1-3/4 inches OD and 1 inch ID, has a sharp tip on one end. To begin site characterization the penetrometer tube is placed into the hydraulic ram then the tube is pushed into the ground. Sensors are mounted in the penetrometer tube to measure contaminants in the surrounding soil and ground water. This system has several distinct advantages over conventional drilling techniques. Additionally, site characterization can be performed much quicker than standard drilling techniques. Fiber optic chemical sensors are readily applicable towards use in cone penetrometer systems since they are small in size and can report real time, in-situ results. Some fiber optic chemical sensors have been deployed and tested in the cone penetrometer system.

Fiber optic sensor system for detection of organic contaminants in soil

A fiber optic infrared (IR) spectroscopic system to be used with the cone penetrometer has been developed. This system can be used to perform real time, in-situ site characterization and analysis by identifying and quantifying organic contaminants in soil.

Comparison of in situ ionizing radiation effects on Raman and photoluminescence intensity of high OH, low OH silica, and fluoride core fibers

An in situ study of the effects of ionizing radiation on the strength of the Raman and photoluminescence signal of high OH, low OH, and fluoride core fibers has been performed with 514.5 nm laser excitation. The fibers were irradiated with a 60Co source at a constant dose rate of 560 rads/h. The high OH fiber displayed a much slower decay of the fiber Raman intensity than the other two fibers during irradiation. The fluoride fiber exhibited the quickest decline in Raman signal with the intensity dropping by a factor of 1000 in less than 20 min. The Raman intensity of the low OH silica fiber recovered to greater than 90% of its pre‐irradiation value after a post‐irradiation photoanneal with 488 nm laser light. The silica fibers displayed an increase in intensity of a broad photoluminescence feature centered at 650 nm. However the fiber photoluminescence intensity remained much weaker than the Raman intensity throughout the irradiations.

IR fiber optic chemical sensors for hazardous waste detection

Infrared fiber optic reflectance spectroscopy is a powerful tool for identifying various organic compounds in soils. Using this technique a mixture of benzene and TCE on sand was measured; peaks due to both compounds are readily evident and correspond to the peaks in the pure liquid. At low concentrations of diesel fuel marine (DFM) on sand the band depths scale linearly with respect to DFM concentration. As the DFM concentration increases, the plot of DFM band depth versus concentration becomes nonlinear.