Boron

Boron reaches most people as borax, hauled out of the Death Valley playas in the 1880s by the twenty-mule teams that became a detergent trademark. Its two great technical uses both come from its nucleus and its bonding. Boron-10, 20% of natural boron, has an enormous neutron capture cross-section — roughly 3800 barns — which makes boric acid and boron carbide the standard neutron poisons in reactor control rods and shutdown systems; operators dose boric acid straight into PWR coolant to trim reactivity. Meanwhile adding boron oxide to silica gives borosilicate glass, patented as Pyrex in 1915, whose thermal expansion is a third that of soda-lime glass and which therefore survives a hot dish hitting a cold sink. Boron is also an essential plant micronutrient, and deficient soils give hollow-stemmed brassicas and cracked beets.