color the distinguishing characteristic of quarks that determines their behavior in the strong interaction.
cosmic rays particles of energy radiating from space.
critical mass the minimum amount of fissionable material needed to cause a nuclear explosion.
curie a unit of radioactivity equal to the quantity of a radioactive isotope that decays at 37,000,000,000 disintegrations per second.
cyclotron a circular accelerator in which particles in a magnetic field are propelled by alternating high- frequency voltage, to study interactions.
dalton an atomic mass unit.
decay a process in which a particle gradually disappears and is replaced with a different particle or particles.
deuterium an isotope of hydrogen.
deuteron the nucleus of deuterium, used in accelerator collisions of particles for research purposes.
E = mc2 Albert Einstein's formula, energy equals mass multiplied by the velocity of light squared, which can be used to explain the loss of mass in a nuclear reaction and its ultimate conversion to energy.
electron a subatomic particle or lepton with a negative charge. A cloud of electrons surround an atomic nucleus.
dose a quantity of radiation absorbed by a body.
dosimeter a device containing photographic film, which darkens the more it is exposed to radiation. It is worn and monitored by people who work around radiation sources. Also known as a film badge.
electromagnetic force one of the four fundamental forces of nature, the interaction between particles caused by their electric and magnetic fields. Also known as electromagnetic interaction.
electron a negatively charged particle that moves around the nucleus of an atom.
electroweak force the combined effects of the electromagnetic and weak forces.
elementary particle any indivisible subatomic particle in a nucleus, such as a lepton, quark, weakon, or classon.
exclusion principle the law of physics that states that no two identical particles can have the same set of quantum numbers or occupy the same quantum state. More formally known as the Pauli exclusion principle.
fast neutron a neutron that can produce fission.
Fermilab the Fermi National Accelerator Laboratory in Batavia, Illinois.
fermion a subatomic particle with peculiar angular momentum or spin and which cannot exist in the same state simultaneously as any other fermion. Electrons, protons, neutrons, quarks, and leptons are all fermions.
film badge see dosimeter.
fissile fissionable. The isotopes uranium 235 and plutonium 239 are highly fissile.
fission a nuclear reaction through which an atom is split, releasing massive energy.
flavor designating any one of the types of quarks or leptons. in quarks, the flavors are up, down, charm, strange, top, and bottom. In leptons, the flavors are electron, muon, tau, electron neutrino, muon neutrino, and tau neutrino.
fundamental interaction any one of the four fundamental forces of nature—electromagnetic, weak, strong, and gravitational.
fusion a nuclear reaction through which two atoms combine to form another element, releasing massive energy. It is the primary energy of stars.
gamma ray electromagnetic radiation with a high penetration power, produced by nuclear reactions.
Geiger counter an instrument used to detect and measure the presence of ionizing particles.
gluon a massless subatomic particle that binds quarks through strong force to form hadrons, such as protons and neutrons.
grand unified theory the theory that strong, weak, gravitational, and electromagnetic forces are variations of the same force.
graviton a theoretical subatomic particle or string without mass or charge, a possible unit of gravity.
gravity one of the four fundamental forces of nature, the attractive force or pull created by any mass.
hadron a subatomic particle composed of quarks and antiquarks that interacts strongly with other particles.
heavy water in nuclear reactors, water with a high content of deuterium atoms.
half-life the time it takes half of the atoms in a radioactive substance to disintegrate or decay into another element.
isobars atoms having the same atomic weight but different atomic numbers.
isomers atoms having the same number of neutrons and protons but having different energy states.
isotones atoms with the same number of neutrons but different atomic numbers.
isotopes atoms with the same atomic number but different number of neutrons.
kaon an unstable meson produced in a high-energy particle collision. It contains a strange quark and an anti-up and anti-down quark or an anti-strange quark and an up or down quark.
k meson a kaon.
lamda particle an electrically neutral baryon.
lepton a subatomic particle involved in weak interactions with other particles. Electrons, muons, and neutrinos are leptons.
mass number the total number of neutrons and protons in a nucleus.
mass spectroscope a device that uses magnetic fields and electric fields to measure the mass of charged particles.
meltdown the overheating and melting of the core of a nuclear reactor, due to accidental loss of coolant.
meson an unstable particle composed of a quark and an antiquark that is subject to the strong force.
molecule two or more atoms bound together to form the smallest particle of any one element.
muon a subatomic particle created from a decayed, charged pion. It has a negative charge and itself decays into an electron.
neutrino a lepton with very little mass and no charge and that interacts only weakly. It exists in three flavors: the electron neutrino, the muon neutrino, and the tau neutrino.
neutrons electrically neutral particles, making up part of an atom's nucleus, along with protons.
nuclear physics the study of the atom's nucleus and its components.
nuclear force see strong force.
nuclear reactor a device in which atoms undergo fission and heat energy is created.
nucleon any particle in the nucleus of an atom; a proton or neutron.
nucleus the core of an atom, composed of protons and neutrons. Its plural form is nuclei.
nuclide any of a class of atoms having the same number of protons, neutrons, and energy content.
orbitals orbiting paths where one or two electrons will almost always be found around a nucleus.
particle a subatomic object with both mass and a charge.
Pauli exclusion principle see exclusion principle.
photon a massless subatomic particle, the quantum unit of electromagnetic radiation or light.
pi meson a pion.
pion part of the binding force of an atomic nucleus, any one of three types of mesons with a positive, negative, or neutral charge.
positron the antiparticle of the electron.
proton a positively charged particle, making up part of an atom's nucleus.