Ambient Xe-133 levels in the northeast US

Measurements of Xe-133 (tau(1/2) = 5.2 days) atmospheric concentrations were performed during the fall of 1993 and throughout 1995 on 'noble gas concentrates' from the northeastern US, These samples were obtained from a commercial air-reduction plant in Allentown, Pennsylvania. Following chromatographic purification of the xenon gas, the Xe-133 activity was determined using a high-purity germanium gamma-ray spectrometer. The average Xe-133 concentrations were in the range 1-3 mBq m(-3), which is consistent with nuclear power plant noble gas releases in the region surrounding the sampling point, but approximately 50-100 times lower than those reported in Albany, NY approximately 300 km to the northeast from 1975 through 1984. The lower atmospheric concentrations are also consistent with the 100-fold reduction in radioxenon release from 25 nuclear reactors in that legion, Only an upper limit could be established for the Xe-135 level (tau(1/2) = 9.1 h), which was about 0.03 of the Xe-133 level, These background levels are of concern in monitoring for atmospheric radioxenons to assure compliance with a Comprehensive nuclear Test Ban Treaty (CTBT). Published by Elsevier Science Ltd.