Cf Californium 98 (251) 7 f 98 [Rn] 5f10 7s2 2 8 18 32 28 8 2 None Unknown 1.3 {"1":"608"} 608 3 10.0 1 900.6 y 1.3×10³y AlphaEmission Solid, Actinide, Radioactive, Synthetic kal-eh-FOR-ni-em Synthetic radioactive metal. Powerful neutron emitter. It has no significant commercial applications. Made by bombarding curium with helium ions. eG6HyPrTccI Californium

Thallium was discovered spectroscopically by Sir William Crookes in 1861, in London.

In 1862, Claude-Auguste Lamy used a spectrometer to determine the composition of a selenium-containing substance which was deposited during the production of sulfuric acid from pyrite.

He noticed the new green line in the spectra and concluded that a new element was present. From Greek thallos, meanin a green shoot or twig 98 1950 Glenn T. Seaborg, Stanley G. Thompson, Albert Ghiorso, Kenneth Street USA Named after the State and University of "California", USA

Thallium and its compounds are highly toxic

Agatha Christie made use of thallium's toxicity in her novel The Pale Horse

Thallium selenide has been used in a bolometer for infrared detection.

Thallium is also used in gamma radiation detection equipment.

Thallium oxide has been used to produce glasses with a high index of refraction, and is used in the manufacture of photo cells.

Some of the electrodes in dissolved oxygen analyzers contain thallium.