A complex of equipment was designed for taking xenon samples from the ambient air, measuring concentrations of radioactive xenon isotopes ( 131 m Xe, 133 m Xe, 133 Xe, and 135 Xe), and transmitting results in the automatic mode. Xenon is extracted from the air stream using low-temperature adsorption on activated charcoal. Radiochemical purification of the adsorbed xenon is based on thermal desorption in a helium stream and the passage of gases liberated by the adsorber through a system of traps. The radionuclide concentrations in xenon samples are determined using the βγ coincidence method. When processing air samples of volume 12 m 3 and measuring their spectra over 10 h, the minimum detectable concentration of the prevailing radionuclide ( 133 Xe) in the air is no greater than 0.5 mBq/m 3 . The complex is designed for radiation monitoring under the Comprehensive Test Ban Treaty.
In the course of testing new devices for measuring atmospheric concentrations of radioactive noble gases and also of the monitoring techniques, large number (116) of determinations of Xe in surface air of St. Petersburg was made (100 in the period from December 1997 to December 1998 and 16 in the second half of March 2000). In 1998, samples were taken at 6-h to 7-day intervals with documentation of data on the wind direction, and in 2000, at 1-day intervals, but without fixing the wind direction. Statistical treatment of data obtained in 1998 gives the mean volume activity of 2.3 + 0.6 mBq m !3 . In 1998, this value was exceeded in three cases by a factor of 233 and in six cases by a factor of 5316. In March 2000, even higher values were observed, exceeding by a factor of up to 43, which was caused essentially by releases from the Leningrad NPP. Data obtained in 1998 also show that the specific activity of 133 Xe depends on the wind direction.
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