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DETERMINATION OF FLUORINE IN GEOCHEMICAL REFERENCE MATERIALS AND COAL BY INSTRUMENTAL PHOTON ACTIVATION ANALYSIS
Abstract
Fluorine as one of the most abundant trace elements in coals is released into the air by combustion and pyrolysis of coal. The produced fluorine gaseous compounds, particularly hydrogen fluoride, are harmful due to their toxicity to living organisms and as a source of corrosion of metallic and ceramic materials. Reliable determination of generally very low concentrations of fluorine in coal (ten to hundred ppm level) is difficult. Standard analytical methods require tedious procedures for sample decomposition and dissolution, and chemical conversion of fluorine into the anionic form. The present work has been aimed at studying possibilities of nondestructive determination of fluorine in coal and other geological materials by instrumental photon activation analysis (IPAA) using the MT-25 microtron. The determination has been based on counting of the non-specific 511 keV annihilation gamma rays of 18F, product of the photonuclear reaction 19F($\gamma$, n)18F and a pure positron emitter. The determination is interfered by simultaneous formation of several other positron emitters, particularly 45Ti and 34mCl. Interference contributions from 22Na, 44Sc, 89Zr, 74As, and 84Rb are small or negligible. By optimization of beam energy and irradiation-decay-counting times, and using correction standards for the interfering nuclides, IPAA allowed determination of fluorine in selected USGS geochemical reference materials and NIST coal standards down to the ten ppm level. The optimized procedure has been applied to assaying fluorine in selected coals mined in the Czech Republic.
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References10
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