Development of the ^<40>Ar- ^<39>Ar dating method based on the Ar extraction from a sample by using a laser beam.

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The main aim in this study is to develop the ^<40>Ar- ^<39>Ar dating method by extracting Ar gases from a sample with the aid of a laser beam. Through this study, we have examined fundamental problems in extracting Ar gases from a mineral under different conditions and obtained a prospect that the ^<40>Ar- ^<39>Ar dating would be possible with the amount of extracted Ar gases by this method.Through this study, it has been revealed that the efficiency of heating a sample with a laser beam is controlled by many factors such. as the concentration of a laser beam, an angle of incidence of a laser beam to the surface of the sample, the efficiency of used lenses, the out-put power of the laser generator and so on. To observe the condition of the surface of a sample, an optical microscope is efficient, but is not always compatible with the best condition for the laser irradiation. We are trying to using a video system to observe the sample during a laser irradiation. There remain some problems in future, among which the estimate of the temperature on the surface of a sample during a laser irradiation, the estimate of a volume of a fused part by a laser irradiation and the fusing of a high temperature felscic mineral are included. In addition, to date a young volcanic rock of less than 10Ma with this method, it is essential to use a high sensitive and precise mass spectrometer to measure the very small amount of Ar degassed by a laser beam from a sample.