Neutron poisons

Boron is a chemical element; it has symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the boron group it has three valence electrons for forming covalent bonds, resulting in many compounds such as boric acid, the mineral sodium borate, and the ultra-hard crystals of boron carbide and boron nitride.

Hafnium is a chemical element; it has symbol Hf and atomic number 72. A lustrous, silvery gray, tetravalent transition metal, hafnium chemically resembles zirconium and is found in many zirconium minerals. Its existence was predicted by Dmitri Mendeleev in 1869, though it was not identified until 1922, by Dirk Coster and George de Hevesy. Hafnium is named after , the Latin name for Copenhagen, where it was discovered. The element is obtained only by separation from zirconium, with most of the world's hafnium production coming from processes that also produce zirconium. These processes make use

Europium is a chemical element; it has symbol Eu and atomic number 63. It is a silvery-white metal of the lanthanide series that reacts readily with air to form a dark oxide coating. Europium is the most chemically reactive, least dense, and softest of the lanthanides. It is soft enough to be cut with a knife. Europium was discovered in 1896, provisionally designated as Σ; in 1901, it was named after the continent of Europe. Europium usually assumes the oxidation state +3, like other members of the lanthanide series, but compounds having oxidation state +2 are also common. All europium compoun

Gadolinium is a chemical element; it has symbol Gd and atomic number 64. It is a silvery-white metal when oxidation is removed. Gadolinium is a malleable and ductile rare-earth element. It reacts with atmospheric oxygen or moisture slowly to form a black oxide coating. Gadolinium below its Curie point of is ferromagnetic, with an attraction to a magnetic field higher than that of nickel. Above this temperature it is the most paramagnetic element. It is found in nature only in an oxidized form. When separated, it usually has impurities of the other rare earths because of their similar chemical

Holmium is a chemical element; it has symbol Ho and atomic number 67. It is a rare-earth element and the eleventh member of the lanthanide series of elements. It is a relatively soft, silvery, fairly corrosion-resistant and malleable metal. Like many other lanthanides, holmium is too reactive to be found in native form, as pure holmium slowly forms a yellowish oxide coating when exposed to air. When isolated, holmium is relatively stable in dry air at room temperature. However, it reacts with water and corrodes readily, and also burns in air when heated.

chemical compound

Borax (also referred to as sodium borate, tincal () and tincar ()) is a salt (ionic compound) normally encountered as a hydrated borate of sodium, with the chemical formula . Borax mineral is a crystalline borate mineral that occurs in only a few places worldwide in quantities that enable it to be mined economically.

chemical compound

thumb|alt=The nucleus is depicted by two red circles with inscribed plus symbols and one purple circle with no inscription. Around the nucleus there is a black ring - a symbol of an electron shell. On it are two teal circles with inscribed minus symbols, depicting electrons.|Diagram of a Helium-3 atom Helium-3 (3He see also helion) is a light, stable isotope of helium with two protons and one neutron (in contrast to the more common isotope, helium-4, which has two protons and two neutrons.) Helium-3 and hydrogen-1 are the only stable nuclides with more protons than neutrons. It was discovered

thumb|The orthoborate anion, a simple borate anion A borate is any of a range of boron oxyanions, anions containing boron and oxygen, such as orthoborate , metaborate , or tetraborate ; or any salt of such anions, such as sodium metaborate, and borax . The name also refers to esters of such anions, such as trimethyl borate .

chemical compound

substance with a large neutron absorption cross-section, which degrade nuclear fission chain reactions in reactors

chemical compound

Xenon-135 (135Xe) is an unstable isotope of xenon with a half-life of 9.14 hours, decaying to long-lived caesium-135.

problem in nuclear reactor start-up

chemical compound

chemical compound