[SGC40-P03] Determination of halogens in some standard materials using the neutron irradiation noble gas mass spectrometric technique
Keywords:Halogen, Noble gas, Nuetron irradiation, Noble gas mass spectrometry
The neutron irradiation noble gas mass spectrometric technique (NI-NGMS) is capable of measuring very low concentrations of halogens (<1 ppb) in very small samples (<1 mg). The NI-NGMS is an extension of the Ar-Ar and I-Xe dating methods [8-10]. Halogens (chlorine, bromine, and iodine) and other elements (potassium, calcium, barium, and uranium) are converted to corresponding isotopes of argon, krypton, and xenon by neutron irradiation in a nuclear reactor. The noble gas isotopes in neutron-irradiated samples are analyzed by noble gas mass spectrometry. Irradiation conditions such as neutron fluence are monitored using standard materials of the Ar-Ar and I-Xe dating methods. Relatively high cross-sections of halogens for neutron capture and high sensitivity of noble gas mass spectrometry enable determination of trace amounts of halogens using NI-NGMS.
We report new halogen concentrations determined for scapolite standards and geological reference materials distributed by Geological Survey of Japan and US Geological Survey using NI-NGMS. Consistent results with those regarded as reference values were obtained from scapolite standards, which indicate that the scapolite standards are reliable in halogen analysis. On the other hand, the halogen concentrations obtained from geological reference materials are systematically lower than the reference values for samples with low concentrations of halogens. The higher concentrations reported for the geological reference materials probably result from contamination on the sample surface during preparation of these reference materials. We also propose a fluorine determination method using NI-NGMS based on neon systematics, although reliable determination of fluorine has been thought to be impossible.
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