The discovery of the element krypton was made in 1898 by William Ramsay and Morris Travers. Krypton is a noble gas lying in the 18th group and fourth period on the periodic table. It is represented by the symbol "Kr" and its atomic number is 36. Krypton is a p-block element, and it is colorless and odorless, commercially obtained from the liquefaction and separation from air. In the atmosphere, krypton is available in concentration, about 1 ppm by volume.
There are six stable isotopes of krypton: krypton-78, krypton-80, krypton-82, krypton-83, krypton-84 and krypton-86. The natural abundance for these isotopes on Earth is 0.356, 2.27, 11.6, 11.5, 57 and 17.3 percent, respectively. They all exist as gases, and more than 99 percent enrichment is available for all of the six isotopes.
The unstable isotopes of krypton are more than 15 in number. These include krypton-79 (half-life 1.45 days), krypton-81 (half-life 210,000 years), krypton-85 (half-life 10.73 years), krypton-85m (half-life 4.48 hours), krypton-87 (half-life 1.27 hours), krypton-88 (half-life 2.84 hours), krypton-89 (half-life 3.15 minutes) and krypton-90 (half-life 32.3 seconds). There are other unstable isotopes as well, with half-lives of milliseconds and nanoseconds.
Krypton is widely used in lighting products, because ionized krypton appears whitish, making it a bright light source. It is also used in lighting in flashing airport runway lights. It is also used with other gases to light "neon lights" to produce greenish light. One meter of length is also defined as exactly 1,650,763.73 wavelengths of light emitted from the krypton isotope, krypton-86. Krypton is also used to find leaks in sealed containers, and in medical science to detect abnormal heart openings.