Generation of Radioxenon Isotopes

With the continued population of the International Monitoring System IMS network and the certification of radioxenon laboratory systems, it has become necessary to calibrate and test these systems using as many of the radioxenon isotopes as possible. Several very promising techniques have been explored recently that allow for convenient production of Xe-133, Xe-131m, the short-lived isotope Xe-135, and even the difficult-to-obtain Xe-133m. IMS national and international laboratories have traditionally obtained Xe-133 from medical isotope suppliers. The activity of these medical dose samples is extremely high tilde 740 MBq and requires very careful fume hood work to dilute down to appropriate levels tilde 10 Bq. By waiting for 10 or more half-lives it is possible to reduce the handling regime considerably, while also obtaining a strong Xe-131m signature due to its longer half-life 11.9 days. The short-lived isotope Xe-135 9.14 hr and the longer-lived parent nuclide Xe-133m 2.2-day half-life are never present in these samples. To obtain these isotopes, another source or technique is required. This paper will discuss the two techniques developed and implemented at Pacific Northwest National Lab PNNL and show the results obtained from each technique. The first is an in-house method that allows for on-demand production of two of these isotopes, Xe-133 and Xe-135, using highly enriched uranium HEU and a modest flux neutron source. The second method uses a neutron activation of stable xenon.