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Isotopes of helium
Although there are nine known
isotopes
of
helium
(
He
) (
relative atomic mass
: 4.002602(2)), only
helium-3
and
helium-4
are
stable
. All
radioisotopes
are short-lived, the longest-lived being with a
half-life
of . The least stable is , with a
half-life
of , although it is possible that has an even shorter half-life.
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