Short answers, pulled from the story.
Hafnium is a chemical element with the symbol Hf and atomic number 72, a lustrous silvery gray tetravalent transition metal. It is most often used in alloys with nickel and in the control rods of nuclear reactors, and its oxide insulates transistor gates in integrated circuits at 45 nm and smaller.
Hafnium was discovered by Dirk Coster and Georg von Hevesy in 1922 to 1923 in Copenhagen, Denmark. Its existence had been predicted by Dmitri Mendeleev in 1869, and it was identified in zircon from Norway using X-ray spectroscopy.
Hafnium is named after Hafnia, the Latin name for Copenhagen, where it was discovered and the home town of Niels Bohr. The Faculty of Science of the University of Copenhagen uses a stylized image of the hafnium atom in its seal.
Hafnium and zirconium are extremely difficult to separate because of lanthanide contraction, which makes their chemistry nearly identical. The ionic radius of hafnium(IV) is 0.78 angstrom and that of zirconium(IV) is 0.79 angstroms, so the two cannot be separated based on differing chemical reactions.
Hafnium is used in nuclear reactor control rods because of its high thermal neutron capture cross section, roughly three orders of magnitude greater than zirconium's. Several of its isotopes can each absorb two or more neutrons, and the metal resists corrosion in the harsh environment of pressurized water reactors.
Pure hafnium is not considered toxic, but it is pyrophoric and fine particles can spontaneously combust in air, so the powder is usually wetted with at least 25 percent water. OSHA set a permissible exposure limit of 0.5 mg/m3 over an 8-hour workday, and 50 mg/m3 is immediately dangerous to life and health.