Age Determination of Crustacean Carapaces using ~(228)Th/~(228)Ra Measurements by Ultra Low Level Gamma Spectrometry

摘要

Precise data for ~(228)Th, ~(228)Ra and ~(226)Ra obtained by ultra-low-level gamma spectrometry show that the ~(228)Ra/~(226)Ta activity ratio in crustacean carapaces is the same as in surrounding waters and that after calcification, they do not behave as a closed system relative to seawater. For environmental studies, radioelements have been shown to be useful chronometers for the determination of the time scale of various processes. In particular, radionuciides in the U- and Th-decay series have proved to be powerful time tracers For time scales in the range of months to a few years, the most appropriate daughter-parent couple is ~(228)Th (t_(1/2) = 1.9 yr)/~(228)Ra. Despite its great potential, the use of this couple is often limited by the lownatural radioactivities encountered in diluted media, especially in the marine environment.