Krypton-84

Main isotopes of krypton

Iso­tope Decay abun­dance half-life mode energy (MeV) pro­duct 78Kr 0.36% 9.2×1021 y εε 2.846 78Se 79Kr syn 35 h ε – 79Br β+ 0.604 79Br γ 0.26, 0.39, 0.60 – 80Kr 2.29% is stable with 44 neutrons 81Kr trace 2.3×105 y ε – 81Br γ 0.281 – 82Kr 11.59% is stable with 46 neutrons 83Kr 11.50% is stable with 47 neutrons 84Kr 56.99% is stable with 48 neutrons 85Kr syn 11 y β− 0.687 85Rb 86Kr 17.28% is stable with 50 neutrons
Standard atomic weight (Ar)	83.798(2)

There are 33 known isotopes of krypton (₃₆Kr) with atomic mass numbers from 69 through 101. Naturally occurring krypton is made of five stable isotopes and one which is slightly radioactive with an extremely long half-life, plus traces of radioisotopes that are produced by cosmic rays in the atmosphere.

The spectral signature of krypton can be observed to have several very sharp lines. When krypton is placed into an electric discharge tube, it emits visible light with a distinctive orange-red color.

Krypton-86 was formerly used to define the meter from 1960 until 1983, when the definition of the meter was based on the wavelength of the 605 nm (orange) spectral line of a krypton-86 atom.

Radioactive krypton-81 is the product of reactions with cosmic rays that strike the atmosphere, along with some of the other isotopes of krypton. Krypton-81 has a half-life of about 229,000 years.

Krypton-81 has been used for dating old (50,000- to 800,000-year-old) groundwater.

Krypton-85 is a radioisotope of krypton that has a half-life of about 10.75 years. This isotope is produced by the nuclear fission of uranium and plutonium in nuclear weapons testing and in nuclear reactors, as well as by cosmic rays. An important goal of the Limited Nuclear Test Ban Treaty of 1963 was to eliminate the release of such radioisotopes into the atmosphere, and since 1963 much of that krypton-85 has had time to decay. However, it is inevitable that krypton-85 is released during the reprocessing of fuel rods from nuclear reactors.

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