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Global climate change in either the form of global warming or global cooling is occurring relatively rapidly today. Studies have shown that increased levels of greenhouse gases, especially atmospheric carbon dioxide (CO₂) are the dominate component contributing to the change. A reduction in CO₂ may be influenced by making larger efforts to sequester carbon in soil and therefore to not only keep soil organic carbon (SOC) levels steady but by possibly increasing them through human assistance. Soil sequestration of carbon has been estimated to have one of the largest potentials to sequester carbon in the world. By some estimation up to 2 billion tons of carbon can be sequestered terrestrially. Therefore the efficient and repetitive monitoring of SOC on a local and global scale is a critical issue. The current soil measurement technique utilized around the world is chemical analysis of one form or another. Chemical analysis of soil is a well studied technique that returns relatively accurate results of density, moisture content, and elemental breakdown of a soil. However, chemical analysis is costly, time consuming, and destructive. As a result of the destructive nature of soil chemical analysis, repeated measurements of the same soil site is impossible. Also, due to time constraints, it would be difficult to analyze a large area utilizing chemical analysis. To surmount the inherent issues with chemical analysis a system based on inelastic neutron scattering (INS) is under development for non-destructive monitoring of carbon in soil. It is based on spectroscopy of gamma rays induced by fast (14 MeV) neutrons emanating isotropically from a D-T neutron generator (NG). The calibration of the INS system is a remains a challenge. Calibration of the system is necessary for relating the carbon gamma ray counts from the detectors to a carbon concentration in the soil volume measured. Utilizing a benchmarked Monte Carlo model of the INS system it is possible to create many calibration curves. The advantages of the model are that the calculations require a relatively short amount of time, and that all the soil variables are defined by the user.

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The concept of using an interferometric process to reduce scattered light in optical systems has been examined from a physical optics viewpoint. An experiment is described which illustrates the basic concepts of a particular scheme addressing the important case of a telescope viewing a distant point object whose image is degraded by scattering from dust on the primary lens. A basic conceptual scheme is described, utilizing a modified Twyman-Green interferometer, which introduces a π phase shift and a focal power difference between the arms. The interferometer is inserted into the optical train of an elementary telescope to null the scattered energy while preserving the image intensity associated with the distant point object, thereby enhancing the signal-to-noise ratio. The effect of this interferometer on the image of a distant point object is examined in detail. Computer techniques were used to solve Lommel function based series representations of the diffraction integral, and generate the intensity distributions which are presented as a series of iso-intensity contour maps. The results indicate that a distant point object could be reimaged successfully. Further analytic evaluations reveal specific operating conditions for the interferometer that optimize the peak intensity at the focal plane. A wavefront model was used to derive the radially dependent intensity distribution at the focal plane from the single on-axis scattering point. To evaluate the effectiveness of the scatter-nulling interferometric technique, an analytic expression for the gain in signal-to-noise ratio was developed, utilizing elementary models of a reimaging system with and without the inclusion of a nulling interferometer. Gains up to a factor of 10⁸ were observed with the assumption of a reasonable set of system parameters and for the limited set of conditions employed. Results imply that the interferometric approach could be successful and effective under restricted conditions. Imagery from the experimental arrangement is presented showing a projection of the concentrated distant source image along with the broad null field from the scattering source.

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An ultrasound spectrometer was designed, constructed and used to measure the frequency dependence of forward-scattered ultrasound from biological specimens. A piezoelectric transducer was continuously tuned through the frequency range of 150 to 400 MHz, producing ultrasound of the same frequency. Pulse modulation of the input signal permitted a frequency resolution of 2 MHz. The received pulse was detected at various temporal positions of its amplitude, thereby allowing measurement of the interference of the scattered and unscattered ultrasound radiation. Because of system nonlinearities all received signals were calibrated with respect to the attenuation of ultrasound in water over the system frequency range. The attenuation of water over the frequency range of 150 to 400 MHz was consequently measured and the values agreed very well with figures given in the literature. Forward-scattering experiments were performed with both physical objects and biological specimens. Sapphire spheres and plastic cylinders exhibited the expected Mie scattering resonant structure. Planar glass plates showed the commonly observed Fabry-Perot resonant structure. Measurement of the resonant frequencies agreed well with theoretically-predicted values. The biological specimens consisted of various cell suspensions of densities on the order of 100 million cells per milliliter. Because of the high cell densities necessary for signal measurement, only signal attenuation was measured. No resonant structure was observed. Synchronized growth colonies of mouse leukemia cells were investigated at both the plateau and log stages of cell growth. The attenuation of melanoma cells was measured with and without melanin. Also, various lines of tumor cells were investigated. For all of these cell suspensions, the attenuation in dB/mm increased linearly with the logrithm of frequency. Though the slope of the attenuation-frequency curves varied from cell line to cell line, the variation for the same cells under different biological conditions was not appreciable. For all of the above cell lines, no attenuation fell out of the range of 5 to 55 dB/mm.

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No description available.