DIAL's Research Highlights

Characterization of Heavy Metals and Radionuclides

On-line Isotopic Analytical System for Uranium and Other Actinides

Using spectral imaging, location of the optimum excitation position within the ICP plasma has been determined for uranium. The enriched U-235 solid received at the end of March was dissolved, and a standard stock solution was prepared for us in Biochemistry. In collaboration with the CRDS group, LIF experiments were performed with solutions containing varying amounts of U-235 and U-238 to ascertain if a dye laser (such as CRDSÕs) is capable of isotopically resolving selected uranium transitions. We have now demonstrated that isotopic resolution of selected uranium transitions is possible with such a system. This completes one of the milestones of the LIF portion of this effort.

Isotopic resolution for uranium was also obtained using CRDS. Both the 286.6 nm and 358.4 nm transitions have been isotopically resolved, yielding detection limits of approximately 150 and 300 ppb respectively for U-235. The U-238 detection limit is slightly higher (600 ppb) for the 286.6 nm line because of a small background absorption line in the plasma. Detection of U-235 at its natural abundance level (0.7%) was demonstrated as well using a U-235 concentration of 1.25 ppm. However, the ultimate detection limit for U-235 in a natural abundance background has not yet been established.

Although various excitation/detection transition pairs have to date been investigated using depleted uranium solutions, the optimum excitation/detection transition pair has not yet been selected - the ideal excitation/detection pair combines a large isotopic separation with high transition probability and high lower-state population. Because of the small wavelength difference between some possible excitation/detection transition pairs, the LIF group has not been able to investigate these combinations with existing apparatus. This difficulty will be overcome when we receive our new spectrometer system and our new tunable dye laser system.

The CRDS work is now focusing on evaluating performance for absorption lines accessible to blue diode lasers. This work will initially be carried out using the existing pulsed dye laser prior to the arrival of the blue diode laser. If successful, the use of such a laser would dramatically decrease the size of the system. This laser can also be tested for use with LIF.

Laser Probe for Technetium

Preparation for the two pulse excitation LIBS experiments began. We plan to use the laser pulses from two laser systems in the initial study. A Quanta Ray DCR-1 laser will be used to generate high intensity plasma and ablate the sample. The Continuum Surelite III laser will be used to excite the sample in the plume. Work to set up the DCR-1 laser is in progress. A triggering scheme will be designed to allow the interpulse interval to be adjusted from 0 to 100 microseconds.

A paper entitled "Enhancement of laser-induced breakdown emission in the presence of external magnetic field" was presented at the American Physical Society April meeting held in Washington, DC.

Development of Tools for Long-term Monitoring

Monitoring Plant Status in Contaminated Environments by Spectral Imaging

During the month of April, design of a system for growing plants of interest (such as Indian mustard) under controlled conditions was finalized, and acquisition of components began. Assembly of the system and planting is expected in mid-May. A graduate student with expertise in agriculture and remote sensing has been recruited to work on this project.

The inability to frequently borrow a portable spectroradiometer system until our dedicated portable spectroradiometer is received may slow initial progress toward selection of spectral region(s) for monitoring.

Application of Imaging Techniques

Thermal imaging. The near-infrared (NIR) camera system was received from the manufacturer. A digital frame communication board for the camera was procured and installed. The system functionality test was completed. The new version of imaging acquisition and process drivers system software was installed. Modification of current thermal imaging system packages was completed.

Image acquisition via the high-resolution (1024 x 1024 pixels) visible digital camera was developed. System calibration against a blackbody is underway. Prototype NIR thermal imaging system development will continue.

Support of RIC project experiments: the thermal images, measured through the top port on the AVS furnace, were acquired, analyzed and presented to the system operators in near real time.

Profilometry. Image acquisition via the high-resolution visible digital camera has been developed. Application for the Fourier transform profilometry (FTP) system is underway. The new version of the imaging acquisition and processing drivers system was installed. Modification of current system packages is underway. The FTP system was improved with the 2-D fast Fourier transform (FFT) modules, and a median filter algorithm was integrated into the system.

We will continue our work on modification of the current FTP system packages for the newly installed imaging acquisition and processing drivers. The FTP system development for a higher resolution camera will follow. The study on phase unwrapping algorithms for target areas with large height discontinuities and/or surface isolations will also continue.

Spectral imaging. Significant progress was made on the development of a computerized spectral imaging system. The system was tested in our laboratory for real time spectral image acquisition. The spectral imaging system was utilized in support of DIALÕs effort to develop techniques for rapid determination of the isotopic abundance of uranium by determining the optimum excitation position for uranium in an inductively coupled plasma (ICP).

The UV AOTF manufacturer is making progress toward completion of our system; delivery is currently expected in mid-summer. Progress on the instrumentation development component of this project will be slow until the UV AOTF system is received.

Hanford Tank Waste Chemistry

Saltcake Dissolution and Enhanced Sludge Washing

Evaluation and fitting of the solid liquid equilibrium data for the Na-F-NO₄-OH system continued. Model calculations in support of actual tank core sample dissolution experiments were completed. The results are being compared to those obtained for other saltcake core samples. Preparations were made for the saltcake dissolution workshop and review to be held in Richland in May.

Laboratory studies continued on the Na-F-OH-NO₃ and Na-SO₄-CO₃-OH systems. Time-dependent evaluations of equilibrium were initiated on the former system, while analysis of carbonate using both a titration method and a TIC analysis were started on the later. Data for other time dependent measurements were collected and analyzed.

Feed Stability and Transport - Prevention of Solids Formation

The sensitivity study of the engineering tool transport model continued. In brief, three Normal distributions, each with the same average particle size but with different widths, were compared to a monodisperse distribution with the same average. In the first portion of the study all of the other parameters, namely, the viscosity, the phase densities, and the velocities were all kept constant. Differences in the sedimentation behavior of the particles were only observed for the larger particles in the distribution. In most cases these changes were small. Keeping the PSD constant and varying the viscosity and the phase densities indicated that these parameters have a significant impact on the transport behavior. Results are being correlated with a one-dimensional model to assess assumptions involved in the development of the simple models.

The DIAL imaging system was used to follow the formation of the sodium phosphate dodecahydrate plug during experiments on the salt well pumping test loop. Images were collected using a 150 mm focal length lens and this permitted a spatial resolution of around 76 microns. Images were collected from the incipient formation of particles through the agglomeration and deposition phases of the plug formation process. The data are being analyzed and will be compared to the one-dimension model and eventually to the results from the engineering tool. Initial analysis indicates that the particles can remain suspended to diameters as large as 1500 microns. Sedimentation is delayed owing to the low particle densities of the phosphate agglomerates.

Process Monitoring and Control of Toxic Organics

Sampling System for Dioxins, Furans and Other Semi-volatile Products of Incomplete Combustion and Characterization

An extensive search has been conducted to identify the source of valves suitable for use on the sampling system. The parameters included in evaluation of possible selections include material of construction (potential for being coated with an inerting material), void volume of the valve, operating temperature range of the unit, and use of any type of lubricants in the operating assembly. An ideal set of valves has not been identified, however, selections have been made for evaluation purposes.

A set of four 80-watt Peltier thermo-electric cooling units have been obtained and evaluated for temperature control of the analyte trap. A variety of tests have been conducted to determine the adequacy of these units and it has been decided to upgrade to the 150-watt versions of these devices. The 80-watt unit uses a fan cooled heat sink to dissipate removed energy and the 150-watt units must be water cooled. The 150-watt units have been received and water jackets are being fabricated.

Three prototype trap units have been fabricated to evaluate the pressure drop across this entity and to determine the functionality of using the water cooled Peltiers for temperature control.

During the coming month the filter holder for separating particulates from the gas stream will be fabricated. Heating mantles for the transfer lines will be secured from Apex and the necessary valves will be obtained from a variety of vendors. These entities complete the items needed to assemble a prototype of the sampling system that can be evaluated for thermal and operational performance.

Toxic Organic Compound Monitoring Using Cavity Ringdown Spectroscopy

The design for the slit-jet expansion system for CRDS dioxin measurements is being finalized and quotes are being obtained for primary system components. With the help of Harald Oser of SRI, a commercial source for the slit-jet valve has been identified. Calculations are being carried out to finalize the pumping speed specifications for the system turbo-pump in order to maintain the baseline operating pressure during pulsed valve operation. Final vacuum system design is underway.

Experiments continue for evaluating the use of the diode laser cavity ringdown system for VOC detection. Unfortunately, after initial very promising results for chlorobenzene were obtained, the external cavity diode laser (ECDL) system failed. Therefore, experiments are continuing using the distributed feedback (DFB) laser. Although the DL-CRDS system is operating well, the DFB does not provide any significant tuning range, preventing us from tuning to the absorption maximum of the species of interest. However, although the final system sensitivity is can not be determined in this fashion, the general response of the system for different compounds can be evaluated. To date we have data for chlorobenzene, benzene, and toluene and expect to obtain data for dichloro- and trichloro-ethylene in the near future.

The ECDL failure is a significant delay, but we can continue to see how the system responds at the DFB wavelength to various compounds. Different compounds sometimes respond differently in the vacuum system. This type of evaluation can continue using the DFB, and may ultimately prove to be more important than being able to tune to the exact maximum absorption.