ABSTRACT

Boron isotopic ratios ¹¹B/¹⁰B of five hot spring waters from the Kusatsu-shirane area, Japan have been measured mass spectrometrically. Their ¹¹B/¹⁰B values are the same within experimental errors and the average value is 4.087. This suggests that the Kusatsu-shirane area belongs to the group of regions that show higher ¹¹B/¹⁰B ratios. The secular change in the ¹¹B/¹⁰B ratio has also been examined for one of the hot springs (Kusatsu-yubatake) and it is found that the ratio has been invariant (average of five measurements = 4.086) for the past twenty years.