This element was discovered by W. Crookes in London in 1861. The name comes from the Greek thallos (green twig).
TlI 6.1 eV, TlII 20.4 eV.
Behavior in stars
The presence of Tl in the sun is dubious. It seems to be present in a sunspot spectrum (Lambert et al. 1969).
Tl has two stable isotopes, Tl203 and Tl205, which occur in the solar system with respective frequencies 30% and 70%. There exist also 26 short-lived isotopes and isomers.
Tl203 and Tl205 are both produced by either the r process or the s process.
Published in "The Behavior of Chemical Elements in Stars", Carlos Jaschek and Mercedes Jaschek, 1995, Cambridge University Press.