A comparison of two methods of gas chromatography mass spectrometry (GCMS) and a nondispersive infrared technique, photoacoustic radiometry (PAR), is presented in the context of field monitoring a disposal site. First is presented an historical account describing the site and early monitoring to provide an overview. The intent and nature of the monitoring program changed when it was proposed to expand the Radiological Waste Site close to the Hazardous Waste Site. Both the sampling methods and analysis techniques were refined in the course of this exercise.

Two methods for sampling and analyzing volatile organics in subsurface pore gas were developed for use at the Hazardous Waste Disposal Site at Los Alamos National Laboratory. One is Thermal Desorption Gas Chromatography Mass Spectrometry (TDGCMS), the other is Photoacoustic Radiometry (PAR). Presented here are two years worth of experience and lessons learned as both techniques matured. The sampling technique is equally as important as the analysis method. PAR is a nondispersive infrared technique utilizing band pass filters in the region from 1 to 15 {mu}m. A commercial instrument, the Model 1302 Multigas Analyzer, made by Bruel and Kjaer, was adapted for field use. To use the PAR there must be some a priori knowledge of the constellation of analytes to be measured. The TDGCMS method is sensitive to 50 analytes. Hence TDGCMS is used in an initial survey of the site to determine what compounds are present and at what concentration. Once the major constituents of the soil-gas vapor plume are known the PAR can be configured to monitor for the five analytes of most interest. The PAR can analyse a sample in minutes, while in the field. The PAR is also quite precise in controlled situations.

Concentrations of volatile organics in a soil pore-gas plume were measured using a commercially available multigas monitor. The monitor is a photoacoustic radiometer (PAR) controlled by an on-board, programmable microprocessor. The measurements determine the extent and location of the vapor plume in the subsurface. At least twelve wells surrounding the sources are measured quarterly. The sources are located in former liquid chemical waste disposal pits and shafts at Los Alamos National Laboratory. The primary constituents of the plume are 1,1,1 trichloroethane (TCA), trichloroethene (TCE), and tetrachloroethene or perchloroethene (PCE). Four quarters of data are presented for TCA. All were used primarily as solvents and degreasers. Previously the composition of the vapor plume was determined by gas chromatography mass spectrometer (GCMS) methods. Photoacoustic radiometry and gas chromatography are discussed giving the advantages and disadvantages of each method, although in this program they are basically complementary. Gas chromatography is a more qualitative method to determine which analytes are present and the approximate concentration. Photoacoustic radiometry, to function well, requires foreknowledge of constituents and serves best to determine how much is present. Measurements are quicker and more direct with photoacoustic methods. Once the constituents to be measured are known, the cost to monitor is much less using photoacoustics, and the results are available more quickly. The photoacoustic radiometer uses narrow band filters in the region where trimmer or higher molecules have vibrational and rotational resonances, from 2.5 to 15 micrometers (4,000 to 650 reciprocal centimeters). The multigas monitor used is a Model 1302 manufactured by Bruel and Kjaer, a Danish company.

In recent experiments at Los Alamos, we directly observed for the first time free-electron laser (FEL) fundamental wavelengths from 20 to 45{mu}m. Our 1988 facility's demonstrated wavelength span now extends from 9 to 45{mu}m. Upgrades are in progress to increase this span. This wavelength region uniquely complements existing FEL applications facilities. 5 refs., 6 figs., 1 tab.

The injector, radio-frequency power system, beam transport, and cavity optics of the Los Alamos free electron laser system have been significantly improved. We report here on experiments to determine the effects of these improvements on extraction efficiency and to demonstrate performance comparable to that found in amplifier experiments and in reasonable agreement with simulations. The experiments used wigglers with 12% and 30% wavelength taper. Measurements were made with and without a prebuncher and with sideband suppression accomplished by cavity-length detuning. The free electron laser produced extraction efficiencies up to 4.4% and showed well-defined buckets of decelerated electrons.

Optical harmonics are naturally generated within free electron lasers (FELs) by the nonuniform axial motion of the electrons within the magnetic undulator. Although far weaker than the optical beam produced at the fundamental lasing frequency, they can provide useful amounts of coherent power at shorter wavelengths. However, UV harmonics can degrade dielectric optics by producing color centers which must be precluded in high power FELs. Up to this time, adequate verification of various theoretical predictions has not been possible because of limited experimental data. To address this problem, we conducted a series of experiments with the Los Alamos infrared FEL oscillator to characterize the power and spatial distribution of the measurable harmonic orders (1, 2, 3, and 5) as a function of electron-beam, undulator, and resonator parameters. The FEL operated at a fundamental wavelength from 10 to 12 μm with a ~20 MeV electron beam with peak current varying from 200 to 500 A.

Plans have been made to modify the Los Almos free-electron laser amplifier experiment to allow its use as an oscillator at 10.6 microns. Several major changes were required, all of which have now been completed. The necessity for these changes is discussed as are the details of their fulfillment. In some cases we have progressed to the point where we can report on the performance of the new systems. The present status is described.

Three kinds of calorimeters, differing in their absorption mechanisms, will be described. Included are surface absorbing calorimeters constructed of beryllium oxide, volume absorbing calorimeters of kapton and copper laminate, and box calorimeters of various shapes constructed of electroformed copper enclosures blackened by the commercial Ebanol* process. In all cases, devices are constructed so that the dominant heat loss mechanism is radiation. That is, they are carefully insulated from their environment. In some cases, drift produced by the background is subtracted by using the twin technique. The heat capacities of the calorimeters are known and the temperature rise is sensed using thermopiles. This gives the energy absorbed. Each device is also calibrated in such a way that it is traceable to the NBS Laser Measurements Standards.

The surface finish of a single-point diamond-turned (SPOT) mirror produced in 1977 on the large (2-meter swing) Excello lathe at the Union Carbide Corporation's Y-12 Plant in Oak Ridge, Tennessee, was such that it was not possible to do visible alignment using it. Therefore, it was necessary to polish the mirror by hand. This was done at the University of Arizona. The intent was to remove the high ridges in the SPDT mirror but not to degrade the figure. Both interferometric and encircled energy measurements were made on the mirror before and after polishing. The mirror was an f/2 off-axis parabola 39.37 cm in diameter. The equation describing the generator of the mother parabola is y2 = 309x(cm2) and the center of each off-axis sister mirror is at x = 7.64 cm, and y = 48.59 cm. After polishing it was possible to align it using techniques which employed visible light. Furthermore, the polished mirror was about 20% better as far as the rms surface figure was concerned, although cosmetically the surface finish appeared visibly degraded after polish.

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text Jon E. Sollid, Scott J. Thomas, Edward Foley, and Claude R. Phipps, "Threshold of detection for various materials at 10.6 μm," Appl. Opt. 17, 2670_1-2671 (1978) Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article