Short answers, pulled from the story.
Swedish chemist Carl Gustaf Mosander discovered terbium in the year 1843 while analyzing yttrium oxide. He identified the element as an impurity within the yellow and pink fractions of a mineral solution rather than as a pure metal.
Terbium orders itself in a simple ferromagnetic state below 219 Kelvin before transforming into a helical antiferromagnetic state as temperature rises. This unique magnetic instability allows the element to act as a bridge between ferromagnetism and antiferromagnetism.
Terbium produces a brilliant lemon-yellow fluorescence that serves as the cornerstone of trichromatic lighting technology. It powers green phosphors in fluorescent lamps and cathode-ray tubes to create white light when combined with europium blue and red phosphors.
Scientists currently extract terbium from ion-adsorption clays in southern China and a massive deposit discovered off the coast of Japan's Minamitori Island in 2018. Estimates suggest the supply from the Japanese deposit could meet global demand for 420 years.
The element has thirty-nine radioisotopes including the stable terbium-159 and the promising terbium-149 with a half-life of 4.1 hours. Terbium-149 is being explored for targeted alpha therapy in cancer treatment due to its nuclear properties.