Exotic nucleus: A nucleus whose proton number (Z) and neutron number (N) are different from those nuclei in the valley of stability. The term is often used synonymously with “a nucleus far from stability” or “a rare isotope.” Such nuclei are unstable and hence decay to more stable configurations.
Fast breeder reactor and fast neutron reactor: The fast breeder reactor is a type of fast neutron reactor designed to produce more fissile material than it consumes. More generally, in fast neutron reactors, fast neutrons maintain the chain reaction. This kind of reactor requires no moderator; instead, it uses enriched fuel and has an efficient neutron “economy.” In the fast neutron reactor, excess neutrons can be used either to produce extra fuel, as in the fast breeder reactor, or to transmute long-half-life waste to less troublesome isotopes, or to do both.
Fission: A process in which the heavy nucleus rapidly divides into two lighter species of roughly equal mass, releasing energy.
Fragmentation: A nuclear reaction process in which the primary high-energy heavy ions irradiate targets of light materials such as lithium or carbon. The breakup of the heavy ion produces short-lived nuclear fragments that have approximately the primary beam velocity. Fragmentation is the opposite of the spallation reaction.
Gas catcher ion source: An apparatus used to provide high-quality beams of rare isotopes of any element except helium. In a gas catcher ion source, high-energy rare isotopes are decelerated by solid absorbers and finally slowed to rest in pure helium gas. Rare isotopes stopped in this way remain charged and can be extracted quickly from the helium gas by a combination of electric fields and gas flow.
Inertial fusion: The achievement of controlled fusion through the tailored implosion of small deuterium-tritium capsules driven by lasers, ion beams, or pulsed power. There are several schemes for carrying out inertial fusion, including direct drive, indirect drive, and “fast ignition,” depending on how the lasers (for instance) are used to deposit their energy and drive the capsule.
In-flight: A production method in which the fragmented exotic nuclei directly exit the production target at velocities similar to those of the primary beam and are isotopically separated and then directly used for experiments.