Isotopes of thallium

Thallium (81Tl) has 41 isotopes with atomic masses that range from 176 to 216.

Thallium-202 (half-life 12.23 days) can be made in a cyclotron[4] while thallium-204 (half-life 3.78 years) is made by the neutron activation of stable thallium in a nuclear reactor.

[5] In the fully ionized state, the isotope 205Tl81+ becomes beta-radioactive, undergoing bound-state β− decay to 205Pb81+ with a half-life of 291+33−27 days,[6][7] but 203Tl remains stable.

[20] It is a radiopharmaceutical, as it has good imaging characteristics without excessive patient radiation dose.

It is the most popular isotope used for thallium nuclear cardiac stress tests.