DETERMINATION OF FLUORINE IN STANDARD ROCKS BY PHOTON-ACTIVATION ANALYSIS

A highly sensitive determination of fluorine in standard rocks by phot on activation using the F-19(gamma,n)F-18 reaction combined with pyroh ydrolysis for the separation of F-18 has been reported. The irradiatio n energy was operated at 20 MeV to avoid the interference from Na, bec ause Na is one of the major element in rocks and F-18 is also produced from Na via Na-23(gamma alpha n)F-18 reaction above its threshold ene rgy, 20.9 MeV. After irradiation, fluorine was extracted by pyrohydrol ysis and separated as LaF3 precipitate. It was ascertained that the av erage recovery of fluorine in standard rocks was about 90% and the pre cipitate was of high radiochemical purity. This method was applied to the analysis of ten GSJ rock reference samples and two USGS standard r ocks issued by the Geological Survey of Japan and the United States Ge ological Survey, respectively. The detection limit of this method was 0.02 mu g/g, and the results obtained by this method were in good agre ement with the recommended values. This method was easily applied to t he determination of a few ppm level of fluorine in rock samples, such as ultrabasic rock and feldspar.