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  • Chemistry  (4)
  • 1
    ISSN: 0049-8246
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Quantitative methods in x-ray fluorescence analysis require a knowledge of the spectral distribution of the fluorescence-exciting beam. The use of XRF yield measurements of a set of thick pure element targets is proposed for the description of a fluorescence-exciting x-ray beam, without the need to obtain its spectral distribution. This new approach is derived theoretically and verified by comparing thin-target yields calculated from XRF yield measurements of thick pure element specimens with those obtained from a calculated spectral distribution. The difference between the two methods of obtaining the thin-target yields is within 9% relative error.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    X-Ray Spectrometry 16 (1987), S. 143-146 
    ISSN: 0049-8246
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The influence of the photons emitted by a 241Am XRF excitation source below 59.6 keV on sample fluorescence production has been analysed. A general method for evaluating the contribution of the various lines from the source in specific equipment configurations is presented. The excitation was performed with 23 elemental targets and the measured experimental intensities were fitted by means of a minimization program which takes into account the most important transition groups observed in the spectrum of the excitation source. The program allows for attenuation of excitation and fluoresced photons in the target. Intensity data for the exciting beam were compared with the theoretical intensities of photons from 237Np, and it was concluded that these values are compatible with the Am and Al thicknesses of the excitation source. Correction factors considering low-energy transitions were calculated for several elements for both thick and thin targets. The over-excitation evaluated for Z = 34 reached values ranging between 180% and 550%.
    Additional Material: 1 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    X-Ray Spectrometry 20 (1991), S. 343-344 
    ISSN: 0049-8246
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: It is shown that the narrow-beam attenuation curve can be a functional description of a low-energy x-ray beam, as is the spectral distribution. Physical quantities, which are usually calculated by integration over the spectral distribution (differential photon or energy fluence), can also be obtained from the narrow-beam attenuation curve without any need for an explicit knowledge of the spectral distribution.
    Type of Medium: Electronic Resource
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  • 4
    Publication Date: 2021-05-19
    Description: The anthropogenic affectation was evaluated on the coast N of the Gulf of Batabanó in May 2003 (corresponding to the provinces of Matanzas and Havana), in areas located in the line of the coast. The results were compared with the historical information of the sector. In the coast N and the Ensenada of the Broa, the parameters oxygen saturation, DBO5 and DQO showed characteristic high values of eutrofication. The biggest contribution in the Cianoficies was in the near coastal areas to sources of organic contamination. In the case of the nutrients they show specific data of mesothrofic waters with tendency to the eutrofization and the silts presented a high affectation for toxic metals. The area near to Guanímar is distinguished to present conditions of organic contamination that favor heterothrofic conditions, corroborated by a prevalence of the processes of mineralization of the organic matter over primary production and lows values of fitoplankton concentration. On the contrary, in the region of Surgidero of Batabanó, the processes of synthesis of organic matter prevail suggested by a high primary production, and concentration of fitoplankton, with low breathing levels and mineralization of the organic matter, that indicates that the system is behaving autothrofically. In a general way, this sector is very affected by the anthropogenic impact. The information obtained is of great importance for the development of the fishing and tourist industries in the area.
    Description: Published
    Keywords: Phytoplankton ; Water quality ; Primary production ; Chemistry ; Environmental monitoring ; Phytoplankton ; Water quality ; Primary production ; Chemistry ; Environmental monitoring
    Repository Name: AquaDocs
    Type: Proceedings Paper
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