DETERMINATION OF THORIUM ISOTOPES IN SEAWATER BY NONDESTRUCTIVE AND RADIOCHEMICAL PROCEDURES

Procedures have been developed for the analyses of dissolved and particulate Th-234, Th-228, Th-230 and Th-232 in seawater. Large volume samples (>1000 1) are collected using in situ pumps. Seawater is pumped sequentially through a filter cartridge and two MnO2 adsorbers for the collection of particulate and dissolved Th, respectively. Both filters-and adsorbers are analysed for Th-234 using a simple gamma counting technique. This newly developed Th-234 procedure can be conducted at sea, and thus provides an easy and efficient method for Th-234 analyses on large volume samples. Subsequent radiochemical purification procedures and low-level alpha counting techniques are used in the laboratory for the analyses of Th-228, Th-230 and Th-232 on these same samples.