This element was discovered by W. Ramsay and M. W. Travers in 1898 in London. Its name comes from the Greek kryptos (hidden).

lonization energies

KrI 14.0 eV, KrII 24.4 eV, KrIII 36.9 eV.

Absorption lines of KrI

No Kr line is seen in the solar spectrum.

Absorption lines of KrII

Following Bidelman's (1960) discovery of KrII in 3 Cen A, this element was observed in some other hot Bp stars. W(4355)=0.025 according to Hardorp (1966).

Emission lines of KrIII

Lines of [KrIII] are seen in the spectrum of at least one recurrent nova (Joy and Swings 1945).

Isotopes

Kr occurs in the form of six stable isotopes and 17 short-lived isotopes and isomers. The stable isotopes are Kr 78, 80, 82, 83, 84 and 86. In the solar system they represent 0.3%, 2%, 12%, 11%, 57% and 17% abundances respectively. Among the unstable isotopes, Kr81 has a half life of 2x 105 years.

Origin

Kr 83, 84 and 86 can be produced by both the r and the s process, Kr82 is a pure s process product, Kr78 a pure p product and Kr80 can be produced by either the s or the p process.