Observations of Environmental Xe-122, Xe-125, Xe-127, and Xe-129m by the Xenon International System

Radioactive isotopes of xenon, 122Xe, 125Xe, 127Xe, and 129mXe, were observed during testing of the next generation xenon measurement system, Xenon International. Xenon International is an automated collection and measurement system designed to detect atmospheric releases of 131mXe, 133Xe, 133mXe, and 135Xe that are used to monitor for nuclear explosions. The observations of 122Xe, 125Xe, 127Xe, and 129mXe radioxenon isotopes occurred along with observations of the four targeted radioxenons during testing at the manufacturing facility in Knoxville, TN, and are believed to be the first identification of these isotopes in environmental samples collected by automated radioxenon systems.

The radioxenon observations are consistent with neutron irradiation of xenon in air (air contains 87 parts per billion xenon) and likely from the High Flux Isotope Reactor (HFIR) or Spallation Neutron Source (SNS) located at the Oak Ridge National Laboratory, located about 20 km away. The isotopes observed can be produced via air irradiation with 125Xe being the most significant and include the radioxenons used for nuclear explosion monitoring (131mXe, 133Xe, 133mXe, and 135Xe) as well as 129mXe, 122Xe, and 127Xe.

The presence of the additional xenon isotopes in the Xenon International beta-gamma detector interfere with the quantification of the nuclear explosion monitoring radioxenons. Additional investigation of the additional xenon isotopes is underway since these observations may increase as more and better-sensitivity system installations occur around the world. Research is ongoing to understand the implications and possible mitigations.