Hydrogen has three naturally occuring isotopes. They
are 1H1, 2H1
(also called "deuterium") and 3H1
(known as "tritium"). Of the three, 1H1
is the most abundant, with deuterium occuring in about a 1:6500 ratio
with 1H1, and tritium in about a 1:1018
ratio.
Tritium is the most interesting since it's radioactive. Tritium has a
half-life of 12.4 years and breaks down like this:
3H1 --> 3He2 +
0e-1
where 0e-1 is a beta particle (electron)
and 3He2 is helium.
You can produce tritium at home by bombarding lithium with neutrons
to make tritium and helium.
6Li3 + 1n0 -->
3H1 + 4He2
This is one of the reactions that take place when a
hydrogen bomb explodes.