Beta Decay - The decay process where an isotope emits an electron (called a beta particle), converting one neutron into a proton to conserve electrical charge. This causes the isotope to become a different element, for example, the beta decay of tritium ³H, with one proton and two neutrons, produces helium ³He, with two protons and one neutron.

Comprehensive Test Ban Treaty (CTBT) - .The CTBT prohibits any nuclear tests producing "yield," a definition which allows ICF research (reasonable), but which prohibits any rapid fission-energy releases that would be useful in developing new nuclear weapons. The CTBT proved impossible to implement during the Cold War, because neither the Soviet Union nor the U.S. seriously considered a CTBT to be in their best interest. Even after the Cold War the CTBT remains controversial, and unlikely to become legally binding since India wants to maintain its nuclear-weapons capability without accepting the responsibilities and costs of being a nuclear weapons state. A subset of the opposition arguments to the CTBT can be viewed here.

Critical Mass - The amount of a fissionable material , at a given density and mixed in a specified way with other material, where on average one neutron caused by a fission reaction will go on to cause another fission.

Cryogenic - Cryogenic conditions are conditions where temperatures are low enough for gases to condense to become liquids or solids. For IFE capsules, deuterium and tritium can be frozen to solid, cryogenic form by the boiling of liquid helium.

Deuterium - Deuterium is the isotope of hydrogen with one proton and one neutron, D = ²H. On average, one out of every 6700 hydrogen atoms found in nature is deuterium. Processes are well developed for separating water molecules containing deuterium atoms, or "heavy water," so that the deuterium fuel for fusion reactions is essentially free. For more information on hydrogen and its isotopes see the Los Alamos periodic table

Electron Volt (eV) - A unit of energy that is convenient to use on the atomic scale, equal to the amount of work required to move an electron, with its negative charge, through an electrical potential of one volt, 1.6 x 10^-19 joules. Chemical reactions at the atomic scale involve energies of a few eV, for example, combining two molecules of hydrogen (H₂) with a single molecule of oxygen (O₂) to make two molecules of water (H₂O) releases 5 eV. Nuclear reactions release much more energy. Fission of a uranium-235 nucleus by a neutron releases 200 MeV -- 200 million electron volts. The fusion of deuterium with tritium releases 17.9 MeV, which, because the mass of the deuterium and tritium are so small, is 500 times the energy released by fission, per kilogram of fuel, and 100-million times the energy released by burning coal.

Entropy - For parents, the concept of entropy is easy to understand, because children inevitably increase entropy, while parents struggle to reduce it. Entropy is a measure of disorganization, which children create when they spread their Happy Meal toys across a room (and perhaps the best measure of economic progress is whether we give our children these opportunities to create entropy). In the context of IFE, the entropy of deuterium and tritium are much lower for D-T ice than D-T gas at the same temperature. The practical result is that D-T gas, when compressed to a high pressure, reaches much higher temperatures than D-T ice, potentially a temperature high enough to initiate a fusion burn. Unfortunately, it takes a lot more energy to compress D-T gas to this temperature--thus the desire in IFE to start with most of the D-T fuel as easily-compressed D-T ice.

Fast Ignition - An advanced target concept where a very rapid burst of energy from a femtosecond (10^-15 laser, rapid pulse of ions, or even a rapid pulse of anti-protons, heats a small spot and ignites fusion fuel that has already been compressed using the conventional ICF method. The great attraction of fast ignition comes from a large reduction in the required driver energy, which in turn could substantially reduce IFE electricity cost.

Fission - The process where a neutron collides with a heavy element like ²³⁵U uranium, causing it to fission into two fission fragments, and release some two to three neutrons and approximately 200 MeV of energy. The fission fragments are radioactive, and create the primary concern for waste disposal and accident consequences.

Half Life - The period of time required for half of a given quantity of an isotope to undergo radioactive decay.

Hohlraum - A metal container that holds a ICF capsule. For more information on hohlraum and capsule manufacture, see Woodworth and Meier (1997). By selecting a high-atomic-weight metal like lead, gold, or tantalum, radiation energy has difficulty penetrating into the metal, and instead primarily heats the inside surface of the hohlraum. This in turn heats the outside surface of the capsule, which sees the hot hohlraum walls.

Ion - An atom which has had one or more of its electrons removed, leaving the atom with a net positive electrical charge equal and opposite to the charge of the electrons which have been removed.

Isotope - All atoms are made up of protons, neutrons, and electrons. Each element has a fixed number of protons: one proton for hydrogen, two for helium, three for lithium, and so on. Elements can have different numbers of neutrons. Isotopes of elements are atoms with the same number of protons, but different numbers of neutrons. Isotopes are defined by the total number of protons and neutrons, for example, deuterium has one proton and one neutron, and is an isotope of hydrogen, D = ²H; and tritium is an isotope of hydrogen with one proton and two neutrons, T = ³H.

Joule (J) - A unit of energy, equal to the work required lift a one kilogram mass a distance of 0.101 meters, or to lift a one pound mass 8.8 inches. For IFE the unit megajoules (MJ), or millions of joules, is convenient. For comparison, the detonation of one kilogram (2.2 pounds) of high explosive releases roughly 4.2 MJ, the combustion of a kilogram of coal releases just over 30 MJ of energy, and the National Ignition Facility's lasers will deposit 1.8 MJ of laser energy into ICF targets. Units of kilojoules (kJ), or thousands of joules; and gigajoules (GJ), or billions of joules, are also used.

Kinetic Energy - Energy associated with the motion of an object, equal to one half times the object mass times the object speed squared.

Kilogram - The kilogram is a unit of mass, equal to 2.2 pounds, or 1,000 grams.

Kilowatt hour - The amount of electrical energy required to provide power at one kilowatt (1000 watts) for one hour. A typical person, working relatively hard, can generate around 200 watts of energy. Such a person would take 5 hours to generate one kilowatt hour, and at current typical electricity costs, would earn from 2 to 10 cents for their five hours of effort.

Lithium - The third element in the periodic table, lithium has three protons and either three (⁶Li) or four (⁷Li) neutrons. The isotope ⁶Li provides the source of tritium for fusion power plants. For more information on lithium see the Los Alamos periodic table

Magnetic-Confinement Fusion (MFE) - In magnetic-confinement fusion, magnetic fields are used to keep moving ions from touching the chamber wall, allowing sufficiently high temperatures and densities to be reached to allow fusion reactions to occur. For more information on MFE, visit the Princeton Plasma Physics Laboratory web site.

Megawatt (MW) - A megawatt is a million watts, sufficient power to light 10,000 100-watt bulbs, or enough electricity for around 3,000 households. The watt is a unit of power, equal to one joule per second. Sometimes the unit MWe, or "megawatt electric" is used to distinguish the electrical power produced by a plant from the larger amount of heat (MWt, or megawatt thermal) required to make that electricity, due to the inherent limitation on the efficiency of converting heat to electricity.

Neutron - Neutrons, which have no electrical charge, and protons, which have positive charge, are the particles which make up the nuclei of atoms.

National Ignition Facility - Located at Lawrence Livermore National laboratory, the National Ignition Facility, or NIF, will use 192 separate high-power lasers to heat ICF targets with a total of 1.8 megajoules of energy. More information about NIF can be found at the National Ignition Facility web site

Nucleus - The center of an atom, consisting of neutrons and protons.

Scientific Notation - Scientific notation provides a convenient way of writing very large and very small numbers. For example, 2.2 x 10⁴ is equivalent to 22,000, and 5.1 x 10^-6 is the same as 0.0000051.

Tritium - Tritium is the isotope of hydrogen with one proton and two neutrons, T = ³H. Tritium decays with a half life of 12.3 years, and thus occurs in nature in concentrations too small to recovered. Tritium, however, can be produced by neutron reactions with the lithium isotope ⁶Li. Tritium is radioactive, decaying by beta decay to the helium isotope ³He. For more information on hydrogen and its isotopes see the Los Alamos periodic table.