» Xenon Xe 127 is a gas suitable for inhalation in diagnostic studies. Xenon 127 is a radioactive nuclide that may be prepared from the bombardment of a cesium 133 target with high-energy protons. It contains not less than 85.0 percent and not more than 115.0 percent of the labeled amount of ¹²⁷Xe at the calibration date indicated on the labeling.