Curium-242

No fission products
have a half-life
in the range of
100–210 k years ...

... nor beyond 15.7 M years

Legend for superscript symbols
₡  has thermal neutron capture cross section in the range of 8–50 barns
ƒ  fissile
m  metastable isomer
№  naturally occurring radioactive material (NORM)
þ  neutron poison (thermal neutron capture cross section greater than 3k barns)
†  range 4–97 y: Medium-lived fission product
‡  over 200,000 y: Long-lived fission product

Curium (Cm) is an artificial element with an atomic number of 96. Because it is an artificial element, a standard atomic mass cannot be given, and it has no stable isotopes. The first isotope synthesized was ²⁴²Cm in 1944, which has 146 neutrons. All of the isotopes are radioactive.

There are 21 known radioisotopes with atomic masses ranging from ²³²Cm to ²⁵²Cm. There are also four known nuclear isomers (^243mCm, ^244mCm, ^245mCm, and ^249mCm). The longest-lived isotope is ²⁴⁷Cm, with a half-life of 15.6 million years – several orders of magnitude longer than the half-life of all known nuclei of elements beyond curium in the periodic table. The shortest-lived isomer is ^244mCm with a half-life of 34 milliseconds.

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Wikipedia