1966 年 14 巻 4 号 p. 177-182
The operation characteristics of a pyrex tube mass spectrometer which was particularly designed for the analysis of very small amount of argon for K-A radiometric dating method is described. The mass spectrometer has very low background: there are no observable background peaks in m/e=36 and 38 and the background in m/e=40 is less than 10-14 ampere during a static operation.
The minimum amount of argon which can be detected by the present apparatus is about 5×10-9cc STP. By means of isotope dilution method, the mass spectrometer can be used for the determination of radiogenic argon of as small as 10-6 cc STP with the precision of ±5% or less and is suitable for the K-A radiometric dating of very young rocks.