Chlorine-36 production and distribution in Australia

Abstract

Chlorine-36 is an unstable isotope of chlorine produced by cosmic-ray bombardment of the atmosphere and the Earth's surface as well as by absorption of cosmic-ray or natural radioactivity-derived neutrons in stable chlorine. Nuclear weapons detonations, nuclear reactors and the use of neutron probes in environmental studies add to the inventory of 36Cl. Radiochlorine is strongly associated with water in the atmosphere, environment, soils and groundwater. Chlorine-36 undergoes radioactive decay with a half-life of 301 ka. These properties make radiochlorine a valuable tracer in the study of aqueous and saline systems and a useful tool for dating closed systems (e.g. confined aquifers). Recent measurements of 36Cl/Cl, using the 14UD tandem accelerator at ANU, show that a variety of processes is important in groundwaters of the Murray-Darling Basin and in the Great Artesian Basin. The results also provide useful information on the levels of 36Cl in soils, salt lakes and other parts of the Australian environment. The results confirm that estimates of 36Cl precipitation rates are reasonable for southeastern Australia but that more information is needed for other regions. Further modelling of chloride movement is also needed, particularly for arid Australia. Show more