Descriptionary

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.

quantum mechanics the physical laws and dynam­ics concerning particles, their electric charges, momen­tum, etc.

quantum theory a theory that states that energy is made up of pulsing quanta and that the amount of energy carried by photons is proportional to the fre­quency of the emitted electromagnetic radiation.

quark a fundamental particle and building block of protons, neutrons, and other elementary particles. There are six variations, or flavors, known as up, down, strange, charmed, bottom, and top.

rad a unit of radiation that is absorbed.

radiation any one of various emissions of energy, including gamma rays, X-rays, neutrons, alpha par­ticles, beta particles, etc.

radiation sickness a potentially fatal illness with such symptoms as nausea, bleeding, hair loss, diar­rhea, and a compromised immune system, caused by overexposure to radiation.

radioactivity emissions of particles or electromag­netic rays.

radioelement any radioactive element.

radioisotope any radioactive substance, whether natural or humanmade.

radiotherapy the use of radiation to treat disease, particularly cancer.

rem a unit used to measure the deleterious effects of ionizing radiation on living tissue, the equivalent of one roentgen of X-rays or gamma rays.

roentgen a unit of exposure of ionizing radiation, as that from X-rays.