AMS MEASUREMENTS OF CL-36 AT CHALK-RIVER

The AMS program at Chalk River continues to be devoted to Cl-36/Cl det erminations. The primary scientific investigations focus on the disper sion of Cl-36 in the Chalk River area, Cl-36 abundances in the Great L ake basin and the residence time of water trapped in the Cigar Lake ur anium ore body. Recent technical advances include: the use of a multi- sample ion source equipped with a spherical ionizer; rapid sequential injection of the Cl-35, Cl-36, Cl-37 isotopes; upgrade to the velocity filter; and detector alterations to match better the spatial extent o f the beam exiting the gas-filled magnet. This magnet is used in all m easurements because it reduces the need for repeated chemical processi ng to reduce sulphur concentrations in the samples with the inherent r isk of Cl-36 contamination from the local environment. In addition, io n-source memory effects, instrument background and the degree of misid entification of unwanted isotopes have been determined and do not limi t isotopic ratio determinations at the 10(-15) level. Preparation tech niques for water, air and rock samples have evolved to the point where backgrounds of 10(-15), 10(-15) and 10(-14) Cl-36/Cl, respectively, c an be achieved in spite of ambient Cl-36/Cl values at this reactor-bas ed research laboratory that exceed 10(-11).