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Thallium-205

Main isotopes of thallium
iso NA half-life DM DE (MeV) DP
203Tl 29.5% is stable with 122 neutrons
204Tl syn 3.78 y β 0.764 204Pb
ε 0.347 204Hg
205Tl 70.5% is stable with 124 neutrons
Standard atomic weight (Ar)
  • [204.382, 204.385]
  • Conventional: 204.38

Thallium (81Tl) has 37 isotopes with atomic masses that range from 176 to 212. 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 (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.

In the fully ionized state, the isotope 205Tl becomes beta-radioactive, decaying to 205Pb, but 203Tl remains stable.



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