Preliminary results on²²⁸Ra/²²⁶Ra in sea-floor hydrothermal fluid around Japan

Abstract

ESR dating of barite is useful to estimate the age of sea-floor hydrothermal activities. The method is based on the fact that radiation from Ra in barite creates SO3- radical which is detected by ESR. Short-lived 228Ra is not detectable in older sample but the radiation from this nucleus cannot be neglected, therefore, the initial value of 228Ra/226Ra in barite is important. In the present study, 228Ra/226Ra was measured by a pure Ge gamma ray spectrometer with Mn fiber dipped in hydrothermal water. Spring waters in Chugoku-area show values of 5-15 while it was 35 for sea-floor hydrothermal fluid in Okinawa Trough.