Short answers, pulled from the story.
Beryllium is a chemical element with symbol Be and atomic number 4. It is a steel-gray, hard, strong, lightweight metal that is brittle at room temperature. Its combination of low density (1.85 times that of water), stiffness roughly 35 percent greater than steel, and the fastest speed of sound propagation among metals (about 12.9 km/s) makes it unique in materials science.
Louis-Nicolas Vauquelin identified a new earth element in emeralds and beryl in a paper read before the Institut de France in 1798. Friedrich Wöhler and Antoine Bussy independently isolated metallic beryllium in 1828 by reacting beryllium chloride with metallic potassium. The name beryllium was first used by Wöhler, and the International Union of Pure and Applied Chemistry standardized that name in 1949.
Berylliosis, or chronic beryllium disease, is a pulmonary and systemic granulomatous disease caused by inhaling dust or fumes containing beryllium. Symptoms can take up to five years to appear, and about a third of patients with the disease die from it; survivors are typically left disabled. The International Agency for Research on Cancer classifies beryllium and its compounds as Category 1 carcinogens.
The James Webb Space Telescope uses 18 hexagonal beryllium mirror segments, each plated with a thin layer of gold, because beryllium contracts and deforms less than glass at the telescope's operating temperature of 33 K. The Spitzer Space Telescope's optics were built entirely of beryllium metal for the same reason. Beryllium's dimensional stability under extreme cold makes it the preferred mirror material for cryogenic space applications.
In 1932, James Chadwick bombarded a beryllium sample with alpha rays from decaying radium and detected the neutron for the first time. The nuclear reaction between alpha particles and beryllium-9 releases a fast neutron and is strongly exothermic. The same reaction is still used today in radioisotope-powered laboratory neutron sources, which produce about 30 neutrons per million alpha particles.
Beryllium forms the beam pipe around the collision region in all four main detector experiments at the Large Hadron Collider (ALICE, ATLAS, CMS, and LHCb). Its low density lets collision products pass through to detectors without significant interaction, its stiffness maintains the vacuum inside the pipe, its thermal stability allows it to function near absolute zero, and its diamagnetic nature prevents interference with the accelerator's magnet systems.