Krypton

⁸⁵Kr has minimal natural production in the Earth, but its concentration in the atmosphere has increased steadily because of human activities related to the nuclear industry. ⁸⁵Kr enters oceans, lakes, and groundwater through equilibration of the water with air. ⁸⁵Kr is produced terrestrially as a fission product of nuclear reactors and released into the atmosphere with the noble gases. It is also produced in the atmosphere via the cosmic ray neutron-activation reaction, ⁸⁴Kr (n, γ) ⁸⁵Kr. Thus, the ⁸⁵Kr specific activity can be used to determine the time since water was isolated from the atmosphere (Fig. IUPAC.36.1). This approach provides a valuable addition to the use of tritium (³H) as an indicator of ocean circulation and groundwater age on decadal (a period of 10 consecutive years) time scales [284], [285]. Krypton stable isotopes react in the upper atmosphere by cosmic-ray-induced spallation and neutron activation to produce radioactive ⁸¹Kr, with a half-life of approximately 2.1×10⁵ years. In the atmosphere, ⁸¹Kr is chemically inert and has a long residence time; because of these characteristics, it is expected that ⁸¹Kr has a relatively constant and well-constrained atmospheric source. Natural cosmogenic ⁸¹Kr is incorporated from air into infiltrating groundwater and has been used to determine the age of groundwater over time scales ranging to over 106 years [286], [287], [288], [289].

⁸⁵Kr has been used as the illumination element of indicator lights of appliances and can be combined with phosphors to create materials that glow in the dark. Light is created when radiation from ⁸⁵Kr strikes the phosphor [98]. ⁸⁵Kr can be used to detect container leaks by placing the radioactive gas inside a container and measuring (with a radiation detecting device) the amount of radioactive ⁸⁵Kr that escapes. Because the gas is inert, Kr will not react with anything else in the container [98].

A patient can inhale gaseous radioactive ⁸⁵Kr, which is then absorbed in the bloodstream, enabling the blood flow of the patient to be studied. Movement of the ⁸⁵Kr can be tracked with a radiation detector to reveal pathways followed by the blood and to quantify blood velocity [99], [284], [290].