Glossary

Facility agreement

Bilateral agreement between the CTBTO and the host country of an International Monitoring System station, which grants the former the legal and administrative authority to work on State territory to establish, upgrade or provisionally operate and maintain monitoring stations.

Facility agreements

Bilateral agreement between the CTBTO and the host country of an International Monitoring System station, which grants the former the legal and administrative authority to work on State territory to establish, upgrade or provisionally operate and maintain monitoring stations.

Fallout

The process of the descent to the earth's surface of particles contaminated with radioactive material from a radioactive cloud. The term is also applied in a collective sense to the contaminated particulate matter itself. The early (or local) fallout is defined, somewhat arbitrarily, as those particles which reach the earth within 24 hours after a nuclear explosion. The delayed (or worldwide) fallout consists of the smaller particles which ascend into the upper troposphere and stratosphere, to be carried by winds to all parts of the earth. The delayed fallout is brought to earth, mainly by rain and snow, over extended periods ranging from months to years.

Feedback Seismometer

A seismometer that measures output signal applying force to the seismometer’s masses to keep them from moving, rather than measuring how much they are displaced. Commonly used in broadband seismometers, the feedback loop works to improve stability and other characteristics of the output signal.

First strike

The launch of a surprise attack to considerably weaken or destroy an adversary's military installations or nuclear forces and thus severely reduce its ability to attack or retaliate (also called “pre-emptive strike”).

Fissile material

Contains elements whose nuclei are able to be split by neutrons of various speeds. Uranium-233, Uranium-235 and Plutonium-239 are all fissile materials. Fissile materials undergo fission more easily than other fissionable materials, and are more desirable for most reactor types and essential for nuclear explosives.

Fissile Material Cut-off Treaty

This proposed multilateral treaty will prohibit the further production of weapons-grade uranium and plutonium. The Treaty has been awaiting negotiations in the Conference on Disarmament since 1996. Also called the Fissile Material Treaty.

Fission

The splitting of the nucleus of a heavy atom into two lighter nuclei. The process is accompanied by the release of large amounts of energy in the form of electromagnetic radiation and kinetic energy of the fission products. Nuclear fission is used for the production of nuclear energy, but also for nuclear weapons.

Fission bomb

A nuclear bomb based on the concept of releasing energy through the fission (splitting) of heavy elements such as Uranium-235 or Plutonium-239. “Little Boy”, the fission bomb dropped on Hiroshima in 1945, was a relatively simple, straightforward, gun-triggered fission bomb that had a 14.5-kiloton yield (i.e. equal to 14,500 tons of TNT) with an efficiency of about 1.5% (i.e. only 1.5% of the material was fissioned before the explosion carried the material away).

Fission chain reaction

The splitting of the nucleus of a heavy atom into two lighter nuclei. The process is accompanied by the release of large amounts of energy in the form of electromagnetic radiation and kinetic energy of the fission products. Nuclear fission is used for the production of nuclear energy, but also for nuclear weapons.

Fission products

Chemical elements created during a nuclear chain reaction, the splitting of the nucleus of a heavy atom into lighter nuclei. Some of these resulting elements are stable, others are unstable and emit radioactivity. This process is called radioactive decay.

Fission weapon

Same as Fission bomb

Fission weapons

Same as fission bomb.

Fizzle

A nuclear explosion with a much lower-than-expected yield due to the chain reaction beginning prematurely.

Flying radionuclide laboratories

A concept of airborne surveillance proposed by the Russian Federation during the negotiations of the CTBT in 1994 as part of the CTBTO’s International Monitoring System. These specially designed aircraft could be called upon by the Technical Secretariat to make sampling flights over remote areas or for use during an on-site inspection and would thus reduce the number of ground-based radionuclide stations required. (This proposal was not adopted.)

FMCT

Same as Fissile Material Cut-off Treaty

Force structure

The configuration of a country's nuclear or conventional forces. In Russia and the United States, nuclear forces are structured in a triad, as nuclear warheads are deployed on bombers, land-based, and sea-based missiles.

Fuel cycle

The series of steps involved in supplying fuel for nuclear power reactors. It can include mining, milling, isotopic enrichment, fabrication of fuel elements, use in a reactor, chemical reprocessing to recover the fissionable material remaining in the spent fuel, re-enrichment of the fuel material, re-fabrication into new fuel elements, and waste disposal.

Full-scope safeguards

Safeguards that apply to all nuclear materials that could readily contribute to the development of nuclear weapons in a non-nuclear weapon state. Monitored by the International Atomic Energy Agency (IAEA).

Fusion

In physics and nuclear chemistry, nuclear fusion is the process by which multiple atomic particles join together to form a heavier nucleus, releasing energy.

Fusion bomb

A hydrogen bomb, also called a fusion bomb or thermonuclear bomb, is a nuclear weapon which utilizes hydrogen isotopes (deuterium and tritium) as a type of fuel. Hydrogen bombs can be many hundreds of times more powerful than fission bombs. The two main types of nuclear weapons are fission weapons (also known as "atomic bombs", "atom bombs" or "A-bombs") and fusion weapons (also known as "hydrogen bombs", "H-bombs" or "thermonuclear bombs"). A nuclear bomb is based on the fusing or burning of light elements (i.e. hydrogen, helium and lithium). Fusion bombs use fission bombs for ignition. See also Hydrogen Bomb and Thermonuclear weapon.