Isotopes of krypton

There are 34 known isotopes of krypton (₃₆Kr) with atomic mass numbers from 67 to 103. Naturally occurring krypton is made of five stable isotopes and one (
Kr) which is slightly radioactive with an extremely long half-life, plus traces of radioisotopes that are produced by cosmic rays in the atmosphere. Atmospheric krypton today is, however, considerably radioactive due almost entirely to artificial Kr.