Isotopes of thallium
has 41 isotopes with atomic masses that range from 176 to 216. 203Tl and 205Tl are the only stable isotopes and 204Tl is the most stable radioisotope with a half-life of 3.78 years. 207Tl, with a half-life of 4.77 minutes, has the longest half-life of naturally occurring radioisotopes.
Thallium-202 can be made in a cyclotron while thallium-204 is made by the neutron activation of stable thallium in a nuclear reactor.
In the fully ionized state, the isotope 205Tl becomes beta-radioactive, decaying to 205Pb, but 203Tl remains stable.Thallium-201
