PROBLEMS OF CONTAMINATION IN CL-36 STUDIES

The joint ANSTO/ANU Cl-36 program has now measured more than 700 samples from many different locations. During the course of this work, a variety of contamination problems have affected a small number of results which have provided valuable information on the effects of ion source cross-talk, sample preparation and storage procedures and sources of high-Cl-36 material. A sample of Weeks Island halite is processed along with every batch of field samples and the observed ratio provides a clear distinction between normal batches and those subject to contamination. Over three years, the long-term average ratio of Cl-36/Cl for normal halite samples is (1 +/- 1) X 10(-15). The sample handling procedures developed during the source of this work provide a useful guide to the techniques that must be used to achieve the sensitivity limits which are potentially available using AMS.