In August, the first noble gas detector in the Comprehensive Test Ban Treaty Organization’s array of monitoring stations was certified ready for use. Among other roles, the organization is tasked with building and maintaining a global network of different types of sensors to detect and measure nuclear explosive tests, whether they take place underground, in the sea, or in the air. Of the 80 planned radionuclide monitoring stations, 40 are planned to be equipped with noble gas detection systems. The system is primarily geared towards detecting xenon, which is a noble gas, and will therefore not react chemically with the environment like other release products. For an underground test, the presence of radioxenon in the atmosphere will be a strong indicator that the explosion was nuclear.
The certified detector is a SAUNA device (short for Swedish Unattended Noble Gas Analyzer) and is based in Charlottesville, US. It is part of radionuclide monitoring station RN75. Uninterrupted sampling of atmospheric xenon is performed using charcoal beds at ambient temperature. Moisture and carbon dioxide is removed from the air using thermoelectric coolers and molecular sieves. Samples are then automatically prepared using ‘preparative gas chromatography’ before the xenon volume is quantified using a thermal conductivity detector.
Noble gas monitoring received worldwide attention in 2006 when North Korea exploded its first nuclear device. Two weeks after the blast, radionuclide station RN16 in Yellowknife, Canada, sensed 0.3–0.6 millibecquerels of xenon-133, a level that results from only 200–400 atoms (see Trust & Verify No. 123). This success prompted the CTBTO to intensify its efforts to fully establish this component of its network. As of August 2010, 26 of the planned 40 stations had been set up. Some 30 stations may be set up by the end of the year, tripling the number that existed at the time of the 2006 explosion in North Korea.
Laurent Rathborn, London.