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Physical Reference Data compiles physical data and biblographic sources: Physical constants, atomic spectroscopy data, molecular spectroscopic data, X-Ray and Gamma-Ray data, nuclear physics data etc.
The primary interaction of low-energy x rays within matter, viz. photoabsorption and coherent scattering, have been described for photon energies outside the absorption threshold regions. These tables are based on a compilation of the available experimental measurements and theoretical calculations. For many elements there is little or no published data and in such cases it was necessary to rely on theoretical calculations and interpolations across Z. In order to improve the accuracy in the future considerably more experimental measurements are needed.
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The Network for the Detection of Atmospheric Composition Change (NDACC), a major contributor to the worldwide atmospheric research effort, consists of a set of globally distributed research stations providing consistent, standardized, long-term measurements of atmospheric trace gases, particles, spectral UV radiation reaching the Earth's surface, and physical parameters, centered around the following priorities.
This database gives values of the basic constants and conversion factors of physics and chemistry resulting from the 2002 least-squares adjustment of the fundamental physical constants as published by the CODATA Task Group on Fundamental Constants and recommended for international use by CODATA.
The Atomic Spectra Database (ASD) contains data for radiative transitions and energy levels in atoms and atomic ions. Data are included for observed transitions and energy levels of most of the known chemical elements. ASD contains data on spectral lines with wavelengths from about 0.2 Å (ångströms) to 60 m (meters). For many lines, ASD includes radiative transition probabilities. The energy level data include the ground states and ionization energies for all spectra. Except where noted, the data have been critically evaluated by NIST. For most spectra, wavelengths, transition probabilities, relative intensities, and energy levels are integrated, so that all the available information for a given transition is incorporated under a single listing. For classified lines, in addition to the observed wavelength, ASD includes the Ritz wavelength, which is the wavelength derived from the energy levels. The Ritz wavelengths are usually more precise than the observed ones. Line lists containing classified lines can be ordered by either multiplet (for a given spectrum) or wavelength. For some spectra, ASD includes lists of prominent lines with wavelengths and relative intensities but without energy-level classifications.