The influence of radiopharmaceutical isotope production on the global radioxenon background.

Radioxenon isotopes play a major role in confirming whether or not an underground explosion was nuclear in nature. It is then of key importance to understand the sources of environmental radioxenon to be able to distinguish them from those of a nuclear explosion. Nuclear power plants were long thought to be the main emitters of these noble gases. Based on new, more sensitive technologies with higher time resolution, recent studies have shown that regions with nuclear facilities have a background of few mBq/m(3) of (133)Xe with short spikes up to few hundred mBq/m(3). These spikes could not in general be explained by normal nuclear power plant operations. Based on several years of measurements, combined with advanced atmospheric transport model results, this paper shows that the main source of radioxenon observations are strong and regular batch releases from a very limited number of radiopharmaceutical facilities in the northern and southern hemisphere. These releases can be up to several orders of magnitude above those attributed to nuclear power plants. This paper reviews the possible production processes of radiopharmaceutical isotopes during which xenon radioisotopes are created. Different production possibilities (with high and low enriched uranium targets) and release scenarios are studied and the total releases are compared with long distance environmental measurements. Further, the ratios of the different radioxenon isotopes are analysed and discussed.