alpha radiation: a form of radioactivity in which the nucleus sends out a helium nucleus with high energy
beta radiation: a form of radioactivity in which the nucleus sends out an electron with high energy
chain reaction: a process in which fission neutrons set off fissions in other nuclei until most of the fissionable nuclei have undergone fission
cold shutdown: a condition in which a reactor core no longer needs a flow of cooling water to keep it from melting
control rod: a rod that absorbs neutrons and can move into and out of a reactor’s core
cooling water: water that absorbs heat from a nuclear reactor and carries it to where its energy can create the steam that drives an electrical generator
critical mass: the amount of mass necessary to cause a chain reaction in a fissionable material
crust: Earth’s rocky outer layer
earthquake: a sudden, powerful shifting of part of Earth’s rocky outer layer or crust
electron: a small, light particle in an atom that carries a negative electric charge
epicenter: the place on Earth’s surface directly above the underground spot where an earthquake begins
fission: a radioactive process in which a nucleus breaks up into two smaller nuclei and several neutrons that carry high energy
focus: the place under Earth where moving plates slip to start an earthquake, also called the hypocenter
fuel rod: a cylinder, which is made of an alloy that does not corrode and which does not absorb many neutrons, that contains pellets of fissionable material
gamma radiation: a form of radioactivity in which the nucleus sends a burst of energy like a powerful X-ray
half-life: the time it takes for half of the nuclei of a radioactive material to disintegrate
hydroelectricity: electricity produced by using rapidly flowing water to drive a generator, also called hydroelectric power
isotope: one of several forms of a nucleus of an element with the same number of protons and a different number of neutrons
meltdown: a kind of accident in a nuclear reactor in which the fuel rods melt
moderator: a substance that slows down fission neutrons so they have a better chance of causing another fission
neutron: a neutrally charged particle in an atom’s nucleus
nucleon: a proton or a neutron
nucleus (plural nuclei): the small central part of an atom that contains most of its mass
plate: a section of Earth’s rocky outer layer (or crust)
prefecture: a Japanese state or province
protron: a particle in an atom’s nucleus that carries a positive electric charge
P-wave: a vibration from an earthquake that is a sound wave with a pitch much too low to be heard. It may be felt, but it causes little damage. It is called a primary wave because it travels faster and arrives before the S-wave, or secondary wave.
radioactivity: a phenomenon in which the nucleus of an atom sends out a burst of energy
reactor core: the portion of a nuclear reactor where it generates its energy
renewable energy: a form of energy that flows naturally and that we can use but not use up
Richter scale: the most common scale used to measure the strength of an earthquake
S-wave: a powerful, often damaging earthquake vibration that shakes the ground up and down or back and forth. It is called a secondary wave because it travels more slowly than the P-wave, or primary wave, and thus arrives later.
spent fuel: reactor fuel that is no longer useful for producing a chain reaction
Tohoku: the region of Japan at the northern end of the main island of Honshu. It consists of six prefectures.
tsunami: a Japanese word for “harbor wave,” a powerful destructive wall of water that rushes in from the sea
turbine: a device that spins to generate power, such as the steam-driven turbines in nuclear power plants or wind-driven turbines in wind farms