Larry A. Jeffers

Method for in-situ detection of tritium in water

The objective of this project was to design a monitoring system capable of detecting and quantifying tritium in-situ in ground and surface waters, and in water from effluent lines prior to discharge into public waterways. The design work was successfully completed with the predicted capability to detect tritium levels below 20 nanocuries per liter. The designed system was based on the detection of the low energy beta radiation from the radioactive decay of tritium using a special form of scintillating optical fiber directly in contact with the water to be measured. To support the design, laboratory tests were performed in several areas. Different types of scintillating fiber were tested to determine which would provide optimum system performance. The fibers contained a fluor material in a special cladding configuration which optimizes the absorption of beta radiation. The tritium detection system consists of an immersible sensor module containing the optical fiber and detection electronics as well as signal processing electronics. An umbilical cable is used to interconnect the components. The system design goals included optional permanent installation for routine water monitoring in wells, process and effluent lines or as a potential portable survey tool which could be moved from one location to another. Not all the design goals were met due to the large physical size of the immersible sensor module. Discussed in this paper are the design details of the in-situ tritium beta detector, the tests performed, and results obtained. The work was supported by U.S. Department of Energy (DOE) contract number DE-AC21-96MC33128.

Performance characteristics of fiber optic lignin concentration sensor

In the paper-making process, wood chips are cooked to form a pulp, which is subsequently washed, bleached, and rolled into sheets. The mechanical strength, uniformity, and amount of bleach necessary to whiten the paper all depend on the lignin concentration in the wood pulp. In this presentation, we describe the developement of a laser-induced fluorescence method to measure lignin concentration in wood pulp, application of the method to characterize hundreds of different pulp samples obtained from different kinds of wood, and correlation of the results with industry-standard wet chemical Kappa number tests. We report the results of detailed characterization tests performed to determine the sensitivity and repeatability of the method and to quantify cross-sensitivity to other variables such as temperature, consistency, and pH.

Multichannel fiber optic temperature monitor

We have developed a multichannel fiber-optic based radiation pyrometer for monitoring the temperature distribution across a moving web up to 4 meters wide. The system employs an array of up to 160 pick-ups whose outputs are delivered by optical fibers to the monitor where they are optically multiplexed onto a 16-channel germanium photodiode array. The pick-ups are deployed linearly across the web on 2.5 cm centers. A 32-channel prototype system achieved a noise limited precision of +/- 1 degree(s)C over the range 140 degree(s)C to 200 degree(s)C. The noise increased to +/- 5 degree(s)C at 100 degree(s)C.

Continuous on-line measurement of lignin in wood pulp

We are working toward the development of an instrument for the continuous on-line measurement of the lignin concentration in wood pulp. The system will be used as a primary sensor for process control in the pulp and paper industry. The measurement is based on the fluorescence properties of lignin. The instrument will use an optical fiber probe to separate the light generation, detection, and analysis equipment from the hostile process environment. To provide the background data necessary for the design of the instrument, we have characterized the fluorescence properties of lignin bound to wood pulp. A nitrogen laser was used as the excitation source and an intensified photodetector array capable of fast grating was used to obtain time-resolved fluorescence spectra.