Browsing by Subject "X-ray spectroscopy"
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Item Observation of fine structures in the k-alpha x-ray lines of chromium and cobalt(Texas Tech University, 1970-08) Shah, Saiyid Masroor,Not availableItem Observation of Fine Structures of X-Ray Lines in Some Transition Elements(Texas Tech University, 1971-08) Priest, John FinleyNot Available.Item Precision x-ray spectroscopy with a three-crystal spectrometer(Texas Tech University, 1968-06) Welch, Herbert EugeneNot availableItem Quasi-monoenergetic laser-plasma acceleration of electrons beyond 1 GeV at the Texas Petawatt Laser(2015-08) Fazel, Neil Behzad; Downer, Michael Coffin; Becker, Michael; Ditmire, Todd; Fink, Manfred; Shvets, GennadyLaser-plasma accelerators first produced 1 GeV electrons with few percent energy spread and high beam quality in 2006. The goal of laser-plasma acceleration experiments conducted at the Texas Petawatt (TPW) laser starting in 2011 was to advance this energy frontier significantly while maintaining high electron beam quality. To maximize energy transfer from laser pulse to electrons, we adopted the strategy of lowering the plasma density so that accelerating electrons and the laser-driven plasma accelerating structure remained in phase over several centimeters, instead of only millimeters. This was only possible because pulses from the TPW laser uniquely have the power (~1 PW) and duration (150 fs) required to excite the plasma resonantly and nonlinearly, and thus to achieve the favorable blowout (bubble) regime, at electron densities as low as 10¹⁷ cm⁻³ . In this dissertation I describe laser-plasma acceleration experiments driven by the TPW laser that successfully accelerated > 10⁹ self-injected electrons (~1 nC) to > 1 GeV (> 10⁸ self-injected electrons > 2 GeV) energy while maintaining < 5% energy spread and submilliradian divergence. These experiments have generated ~2 GeV electron bunches more consistently and in larger numbers than any laser-plasma accelerator in the world. I also describe single-shot diagnostic methods developed to characterize the divergence and energy spectrum of the electrons, and of the betatron x-rays they produced, despite low-repetition rate, significant pointing fluctuations, and electromagnetic pulse (EMP) background. Betatron x-ray radiation originates from the transverse wiggling motion of accelerating electrons in the electrostatic field of a plasma bubble. It is useful as a broadband, femtosecond x-ray source and as a diagnostic of transverse electron beam emittance. Experiments at the TPW laser yielded betatron x-rays that were brighter, more collimated and more energetic than in previous experiments. I describe in depth an x-ray spectrometer design and methodology that I developed for single-shot, spatially-resolved measurement of betatron x-ray spectra. X-rays were sampled through K-edge transmission filters distributed strategically on a planar detector, high-fidelity x-ray images were reconstructed, and iso-intensity contours subsequently defined. I demonstrate how x-ray spectra may be calculated on such contours and used to produce a 3D representation of the x-ray spectrum. This represents the first single-shot method for betatron x-ray spectroscopy offering spatial resolution over the entire range of the x-ray profile.Item Soft X-Ray Band Structure of Metals Using a Spherically Bent Crystal Spectrometer(Texas Tech University, 1971-05) Faulkner, Bobby BainNot Available.Item Surface processes : ruthenium film growth, silicon nanocrystal synthesis, and methylene partial oxidation(2001-08) Smith, Kristen Colleen; White, John M.Item Three crystal spectrometry of copper K alpha lines(Texas Tech University, 1986-08) Tidrow, Steven CBy bombarding a poly-crystalline copper target with 15KeV electrons at lOmA direct current emission, a continuous spectrum of copper radiation was produced and made incident upon a mono-crystal of copper having a purity of 0.9999 and produced for the (111) planes. The mono-crystal of copper was aligned to produce Bragg reflection of the copper Ka lines, which occur in the moderate x-ray region, while simultaneously producing Pseudo-Kossel Ka lines in the same direction as that of the Bragg reflected lines. The spectral output was analyzed using a two quartz crystal spectrometer and multi-channel analyzer. The data shows an unusual increase in the copper Kai to Ka2 ratio, while exhibiting line width narrowing in both of the Ka lines, indicative of stimulated emission.Item Understanding the variations in fluorescence spectra of gynecologic tissue(2004) Chang, Sung Keun; Richards-Kortum, Rebecca, 1964-Optical spectroscopy has shown promise as a diagnostic tool for detecting cervical pre-cancer because spectral variations in optical measurements are closely correlated with the molecular and architectural changes in tissue that accompany dysplastic progression. However, optical measurements from cervical tissue are also affected by other factors, such as age or menopausal status of the patient. In order to develop robust diagnostic algorithms based on optical measurements, it is important to identify diagnostically significant features and to devise methods to extract them from the spectral variations. Principal component analysis (PCA) is a statistical method of extracting features based on the variance in a dataset. PCA applied to fluorescence measurements from cervical tissue revealed biophysically significant spectral variations during the menstrual cycle. We have also applied PCA in developing a classification algorithm to discriminate a pair of diagnostic classes. Although statistical methods can reveal subtle changes in optical spectra that are diagnostically significant, it is difficult to interpret the biophysical significance of the extracted features. Another approach is to extract the tissue optical parameters that are directly related to precancerous changes. In order to perform model-based parameter estimation, an analytical model was developed to describe fluorescence in two-layered tissue such as the cervix. Briefly, the model uses exponential attenuation and diffusion theory, respectively, to describe light propagation in the epithelium and the stroma, and calculates the total detected fluorescence as the sum of the fluorescence signals emitted from the two layers. In the inverse model, the analytical model was iteratively fitted to the measured fluorescence spectra, and as a result of the fitting process, the optical parameters are estimated. Validations with Monte Carlo simulations show that optical properties of the epithelium and the stroma can be estimated accurately. The inverse model was subsequently applied to a large-scale clinical data, and the estimated parameters show good correlation with changes associated with dysplastic progression as well as age.Item X-ray lines close to KLL auger electron energies from Fe, Co, Ni, and Cu monocrystals(Texas Tech University, 1990-08) Koo, Yeon DeogBy x-ray bombardment of metal monocrystals (Fe, Co, Ni, and Cu), x-rays of KLL radiative Auger electrons (KLL RAE) can be observed on the low energy side of the Ka lines. The energies of the KLL RAE x-rays of each monocrystal are the same for different lattice planes and when different kinds of x-ray tubes. Mo, W, and Cu target tubes, are used. Therefore, the peak energies detected within the KLL Auger electron energy limit are interpreted as KLL RAE x-rays. The measured intensity ratios of KLL/Ka are about 0.3%. Additionally, the ratio of I(K/9)/I(Ka) and I(Si escape peak)/I(Ka) are measured. All of these values agree well with theoretical values. The beam shapes of KLL RAE x-rays are studied by taking pictures on x-ray films. The intensity distribution for Ni and Cu are measured by changing the crystal angle with respect to the incident x-ray beam near the Bragg angles of the KLL RAE x-rays. It is shown that the KLL RAE x-rays are very sharp and stimulated when the crystal is set at the Bragg angle of the KLL RAE with respect to the incident beam, which contains both the pumping radiation and Bremsstrahlung of frequencies in the KLL RAE range in which the KLL x-rays stimulation is achieved.