![]() ![]() The specific wavelengths are characteristic of the target material (Cu, Fe, Mo, Cr). K α1 has a slightly shorter wavelength and twice the intensity as K α2. These spectra consist of several components, the most common being K α and K β. When electrons have sufficient energy to dislodge inner shell electrons of the target material, characteristic X-ray spectra are produced. Details X-rays are generated in a cathode ray tube by heating a filament to produce electrons, accelerating the electrons toward a target by applying a voltage, and bombarding the target material with electrons. X-ray Powder Diffraction (XRD) Instrumentation - How Does It Work?īruker's X-ray Diffraction D8-Discover instrument. Powder and single crystal diffraction vary in instrumentation beyond this. A key component of all diffraction is the angle between the incident and diffracted rays. These X-rays are directed at the sample, and the diffracted rays are collected. Typically, this is achieved by comparison of d-spacings with standard reference patterns.Īll diffraction methods are based on generation of X-rays in an X-ray tube. Conversion of the diffraction peaks to d-spacings allows identification of the mineral because each mineral has a set of unique d-spacings. By scanning the sample through a range of 2 θangles, all possible diffraction directions of the lattice should be attained due to the random orientation of the powdered material. These diffracted X-rays are then detected, processed and counted. This law relates the wavelength of electromagnetic radiation to the diffraction angle and the lattice spacing in a crystalline sample. The interaction of the incident rays with the sample produces constructive interference (and a diffracted ray) when conditions satisfy Bragg's Law ( n λ=2 d sin θ). These X-rays are generated by a cathode ray tube, filtered to produce monochromatic radiation, collimated to concentrate, and directed toward the sample. X-ray diffraction is based on constructive interference of monochromatic X-rays and a crystalline sample. X-ray diffraction is now a common technique for the study of crystal structures and atomic spacing. These relationships were extensively tested with surface sediments from the catchments and high-resolution sediment trap data.Max von Laue, in 1912, discovered that crystalline substances act as three-dimensional diffraction gratings for X-ray wavelengths similar to the spacing of planes in a crystal lattice. Different origin and mechanisms of sediment transport (glacial abrasion in dry and hot summers, soil erosion during wet and cold summers) from different sub-catchments with characteristic bedrock mineralogy provide a sound physical explanation for the statistical relationships between differential XRD peak intensity ratios and the climate parameters. All correlations are significant (p < 0.01) and stable in time. Mica/plagioclase and mica/chlorite were positively correlated with autumn SON precipitation (r = 0.68) and summer MJJAS precipitation (r = 0.59), respectively quartz/amphibole and quarz/plagioclase were negatively correlated with annual precipitation (r = -0.67, r = -0.52 respectively) chorite/mica was negatively correlated with autumn SON temperature (r = -0.59). XRD peak-intensity ratios of different minerals were analyzed in each varve for the calibration period (AD 1864 - 1949). The correlation is stable in time and the structure of variations agree very well with independent autumn temperature reconstructions based on documentary evidence. ![]() Annual biogenic silica flux to the sediments yielded a significant correlation against instrumental autumn (September - November) temperatures (calibration period AD 1864 - 1949, r = 0.7, p < 0.01). Annual biogenic silica flux (BSi) and XRD peak intensity ratios were analyzed and calibrated against instrumental temperature data (AD 1864 - 1949 varve counting from AD 1950 onwards is difficult and eutrophication is signifiant) from nearby meteo station Sils Maria, and compared with (i) early instrumental data back to 1760 AD, and (ii) two fully independent temperature reconstructions for the same area (based on dendroclimatological and documentary data) back to 1580 AD. Subsamples were taken in individual laminae year by year. The chronology of the core is based on varve counting, super(137)Cs, super(210)Pb and event stratigraphy. Annually laminated (varved) freeze-core samples of Lake Silvaplana (4627'N, 948'E, 1791 m a.s.l, Engadine, eastern Swiss Alps) provides an excellent archive for quantitative reconstruction of high- and low-frequency climate signals back to AD 1580. ![]()
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