SAUNA III - The next generation noble gas system for verification of nuclear explosions.

The SAUNA III represent the next generation of the SAUNA systems designed for detection of low levels of radioactive xenon in the atmosphere, with the main purpose of detecting underground nuclear explosions. The system automatically collects, processes and measures 40 m3 atmospheric samples every 6 h, increasing both the sensitivity and time resolution as compared the systems currently in use. The higher sensitive increases the number of detections, especially for samples were more than one isotope of xenon are detected. This improves the understanding of the background and the possibility to screen out signal from civilian sources. The increased time resolution of the new system also provides a more detailed picture of the plumes, especially important for near-by sources. The design of the system as well as data from the first two years of operation are presented.