Isotopes of thallium

Thallium (Tl) has 25 isotopes which have atomic masses that range from 184 to 210. 203Tl and 205Tl are the only stable isotopes and 204Tl is the most stable radioisotope with a half-life of 3.78 years.

Thallium-202 (half life 12.23 days) can be made in a cyclotron while thallium-204 (half life 3.78 years) is made by the neutron activation of stable thallium in a nuclear reactor.

Standard atomic mass: 204.3833(2) u

Isotopes of thallium occurring within the radioactive disintegration chains of actinium, radium and thorium were known as:
 * radium EII : 206Tl
 * actinium CII : 207Tl
 * thorium CII : 208Tl
 * radium CII : 210Tl