Short answers, pulled from the story.
Europium was first identified in 1896 by French chemist Eugene-Anatole Demarçay, who suspected that samarium samples contained an unknown element. Demarçay isolated it in 1901 and named it after the continent of Europe. William Crookes had noted anomalous spectral lines in samarium-yttrium ores as early as 1885.
Europium is used as a red phosphor in color television screens and fluorescent lamps, with each color TV screen containing between 0.5 and 1 gram of europium oxide. It also appears in anti-counterfeiting phosphors in euro banknotes and in helical fluorescent light bulbs. Medical and pharmaceutical research uses europium-labeled antibodies to detect antigens in body fluids.
Europium is the most reactive lanthanide because it readily forms both +2 and +3 oxidation states. The +2 state is stabilized by a half-filled 4f7 electron configuration. This means europium reacts with air and water similarly to alkaline earth metals like calcium, and a centimeter-sized piece will begin oxidizing within several days.
The europium anomaly refers to the depletion or enrichment of europium in minerals relative to other rare-earth elements. During magma cooling, divalent europium is preferentially incorporated into certain minerals by ion exchange, leaving lanthanide minerals such as monazite with less europium than the average cosmic abundance predicts. Geochemists use this anomaly to reconstruct how suites of igneous rocks are related.
Europium is mined alongside other rare-earth elements from bastnäsite, monazite, xenotime, and loparite deposits. The Bayan Obo deposit in Inner Mongolia, the largest known rare-earth deposit at an estimated 36 million tonnes of rare-earth oxides, contains only 0.2% europium. The Mountain Pass mine in California, active from 1965 until the late 1990s, contained just 0.1% europium.
Natural europium is composed of two isotopes: 151Eu and 153Eu, with 153Eu being slightly more abundant at 52.2%. While 153Eu is stable, 151Eu undergoes alpha decay with a half-life of 4.6 times ten to the eighteenth years, producing about one alpha decay every two minutes per kilogram of natural europium.