Abstract
The concentration of thorium isoto p es and the activity ratios of 230Th/232Th and 228Th/232Th in 500 / 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 l-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.
