Monitoring the equilibration of ²²⁸Th and decay products over time after extraction from ivory

The worldwide population of elephants shows a rapid decline due to trafficking of ivory. Hence, a method is needed for the age determination to distinguish legal from illegal ivory. The analysis of ²²⁸Th and ²³²Th in ivory can be used for this purpose. This study provides a technique for the analysis of ²²⁸Th in ivory. The thorium was extracted from ivory and measured after various time periods applying α-spectrometry until a secular radioactive equilibrium between ²²⁸Th and its decay products was established. An equilibration period of 32 days was found. The uncertainty of the determination of the activity of ²²⁸Th could be reduced by integrating the counts of the equilibrated decay products into the determination process. (author)