Matter & Energy

Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.


Gadolinium, symbol Gd, silvery white metallic element with an atomic number of 64. Gadolinium is one of the rare earth elements in the lanthanide series of the periodic table. It is named after the Finnish chemist John Gadolin.

Gadolinium occurs with other rare earth elements in many minerals, such as samarskite, gadolinite, monazite, and some varieties of Norwegian ytterspar. It is the 41st element in order of abundance in the crust of the earth. Gadolinium melts at about 1313° C (about 2395° F), boils at about 3273° C (about 5923° F), and has a specific gravity of 7.9. The atomic weight of the element is 157.25.

Gadolinium oxide was first separated from other rare earth elements by the Swiss chemist Jean de Marignac in 1880. The oxide and many salts of gadolinium have been prepared. Gadolinium oxide is white and the salts are colorless.

Because gadolinium has the largest known cross section, or stopping power, for neutrons of any element, it is used as a component of control rods in nuclear reactors (see Nuclear Energy). Like the other rare earth elements, it is used in electronic apparatuses such as capacitors and masers; in metal alloys; in high-temperature furnaces; and in apparatuses for magnetic cooling.