Concentration of Thorium Isotopes and the Activity Ratios of 230Th/232Th and 228Th/232Th in Seawater in the Pacific Ocean

Abstract

The concentration of thorium isotopes and the activity ratios of 230Th/232Th and 228Th/232Th in 500 l sea water samples collected in the Pacific Ocean were determined. Thorium isotopes were analyzed by alpha-ray spectrometry after separating them from other elements with an anion exchange resin. The average content of thorium (232Th) of 0.9 ng 7−1 was obtained in the open Pacific water. The average contents of 230Th and 228Th were 2.1 x 10−2 pg l−1 and 1.2 ag l−1 respectively. It was found that the ratios of 230Th/232Th and 228Th/232Th ranged respectively from 1.0 to 29, and from 0.4 to as high as 128. © 1978, Japan Meteorological Agency. All rights reserved.