New Analytical Method Helps Verify Chemical Weapons Compliance - Page 3

With Origin, it was possible to adjust virtually any component of a plot through interactions with the mouse and dialog boxes. As a result, instead of poring over tables of data or rudimentary plots and missing important information, researchers were able to easily create thousands of highly informative plots, some of which uncovered vital aspects of the SFAI process. For example, in a plot of an acoustic spectrum, one would anticipate seeing regularly spaced peaks. Using Origin's zoom feature, however, it was sometimes possible to pick up unexpected and subtle variations in the spectrum. These slight variations could indicate some new physics that was then incorporated into an algorithm to extract one of the target parameters.

The analysis software's peak fitting feature was first used to derive the liquid's speed of sound and attenuation of sound (see Fig. 1). It was used to find the maxima of resonances, for example, and the differences between them is what indicates sound speed. A width measurement, also obtained from a peak fit, relates to absorption and attenuation of the sound. Rather than requiring weeks of writing subroutines to fit peaks to the data, the process with Origin was simply "point and click." Origin's peak-fitting module included all the necessary spectroscopic fitting equations. It also provided timesaving tools such as automatic determination of peak centers, half-widths, heights, and areas. The simplicity of the peak-fitting process allowed researchers to evaluate many algorithms quickly.

In several cases, the right graphics helped researchers make sense of apparently random data. In one instance, researchers noticed fluctuations on the right side, the high frequency side, of the peaks, and originally believed them to be noise, a nuisance to be smoothed out or tossed out. However, an autocorrelation done with Origin detected a periodic pattern that turned out to be related to shear modes which propagated along the circumference of the container (Fig.2). These shear modes were later directly related to the viscous coupling of the liquid. The result was a unique way to determine viscosity of liquids inside sealed containers. After all the required algorithms for SFAI were determined, they were rewritten as FORTRAN or Quick BASIC programs for use in the detector that is used in the field. The instrument weighs about six pounds, and feeds data into a 486 PC with a customized digital synthesizer and analyzer board from Neel Electronics, Laguna Niguel, California. The computer memory contains a database of the physical properties of all primary chemical warfare compounds. To use the system, an operator simply places the transducers on the item to be tested and presses a button. All measurements and analysis are done automatically. The detector can safely analyze a container in approximately 20 seconds, a significant improvement over early monitoring systems.

In the area of chemical weapons compliance, SFAI is a very needed technology. The Chemical Weapons Convention treaty calls for the eventual destruction of all chemical weapons, making it essential that there is some technique that can quickly and easily monitor compliance. The US Defense Special Weapons Agency has funded this development effort for use in such treaty compliance. This technique can allow "challenge inspections" of suspect munitions without opening or drilling a hole into artillery shells or containers. At this time, SFAI has been successfully tested on a large variety of chemical munitions at government storage depots. During those trials, a developer of the system was on hand to assist with the operation of the detector. The next stage of field trials will be performed by operators who have had no previous experience with the technology.

SFAI has other applications besides determining the content of sealed munitions. It has been shown to be a good technique for characterizing petroleum products and also for detecting spoiled milk in sealed containers such as paper cartons, plastic bottles, and Tetra Pak pouches.

In the development of SFAI, nearly every capability of Origin was used on a daily basis. When the software did not contain a certain analysis, it was either created in-house through Origin's built-in scripting language or OriginLab (formerly Microcal Software) provided it. The company was very responsive to the needs of this project, to the point of delivering a new feature only a day after it was requested. Without Origin, it would have been very difficult to develop the algorithms for this technique.

By Dipen N. Sinha
Electronic and Electrochemical Sensors & Devices Group
Los Alamos National Laboratories
Los Alamos, New Mexico

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