Glossary

Land-based Missile Systems
Missile systems located on land in hardened bunkers and underground silos or on mobile launchers, which are more vulnerable to first-strike attacks. The mobile land-based missile systems are less vulnerable to first-strike because the positions of the missiles can be changed.
Laser Isotope Separation (LIS)
An isotope separation technique in which specific uranium isotopes are excited and ionized by lasers. Also suitable for separating specific plutonium isotopes.
Latin American Nuclear-Weapon-Free Zone
See; Treaty of Tlatelolco.
Layered BMD system
A ballistic missile defense system that consists of several sets of weapons that operate at different phases in the trajectory of a ballistic missile. Thus, there could be a first layer (e.g. boost phase) of defense with remaining targets passed osucceeding layers (e.g., midcourse and terminal).
Lethal Dose (50/30)
The dose of radiation expected to cause death within 30 days to 50% of those exposed without medical treatment. The generally accepted range from 400-500 rem received over a short period of time.
Light-Water Reactor
A reactor that uses natural water as a moderator and coolant, and low-enriched uranium as fuel. The most common type of power reactor currently in use. Must be shutdown to change fuel.
See; Boiling-Water Reactor, Pressurized-Water Reactor, Reactor.
Limited Test Ban Treaty (LTBT)
Another name for the Partial Test Ban Treaty.
See; Partial Test Ban Treaty.
Lisbon Protocol
The protocol was opened for signature in 1992 by Belarus, Kazakhstan, Russia and Ukraine, it made these states parties to the 1991 Strategic Arms Reduction Treaty as successors to the former Soviet Union. Belarus, Kazakhstan, and Ukraine also committed themselves in that protocol to adhere to the nuclear Nonproliferation Treaty (NPT) as non-nuclear weapon states.
See; Strategic Arms Reduction Treaty
Lithium Deuteride
Used as the fuel for the fusion bomb. A neutron is added to the lithium, producing tritium which is in turn fused with the deuteride.
See; Deuterium, Tritium, Hydrogen Bomb.
Little Boy
A 12.5 kiloton fission bomb dropped on Hiroshima, Japan on August 6, 1945. It killed 80,000 people and injured over 120,000 more.
See; Hiroshima, Fission Bomb, Fission, Gun-Type Weapon, Manhattan Project.
Lop Nur
The People's Republic of China tests its nuclear weapons at Lop Nor. The first Chinese-made atom bomb (a fission device) was tested there on October 16, 1964; the first guided missile on October 27, 1966; and the first thermonuclear (fusion) device on December 28, 1966.
Los Alamos National Scientific Laboratory
Los Alamos National Scientific Laboratory, a research center devoted to the applications of nuclear energy and to national defense, occupies a 199 sq km (77 sq mi) site in the Jemez Mountains in north central New Mexico. The laboratory, founded in 1943 as the Atomic Research Laboratory, is operated by the University of California and funded by the U.S. Department of Energy. Scientists at Los Alamos developed the first atomic bomb and the first U.S. hydrogen bomb. The laboratory program has now extended to the peaceful uses of atomic energy and basic research in such fields as physics, biology, chemistry, geothermal energy, and medicine.
Low-enriched uranium (LEU)
Uranium in which the naturally occurring U-235 isotope is increased, to less than 20 percent and usually between two and four percent. LEU is used in nuclear fuel for reactors using natural (light) water as a moderator and coolant.
Low-level waste
Radioactive waste not classified as high-level waste, transuranic waste, spent nuclear fuel or byproduct material.
Lucky Dragon
The Fukuryu Maru (Lucky Dragon) was a small Japanese tuna boat, fishing about 90 miles east of Bikini at the time of the BRAVO test. About two hours after the explosion a 'snow' of radioactive ash composed of vaporized coral began to fall on the ship. Within hours, the crew members began to experience burning and nausea. Upon returning to Japan, many were hospitalized and one eventually went into a coma and died. Though the U.S. denied responsibility, it sent the widow a check for 2.5 million yen "as a token of sympathy."
See; BRAVO Test.
Mach Stem
The shock front formed by the merging of the incident and reflected shock fronts from an explosion. The term is generally used with reference to a blast wave, propagated in the air, reflected at the surface of the earth. The Mach stem is nearly perpendicular to the reflecting surface and presents a slightly convex (forward) front. The Mach stem is also called the Mach front.
Manhattan Project
The Manhattan Project was the code name for the U.S. effort during World War II to produce the atomic bomb. The program was under the leadership of Gen. Leslie Groves, and theoretical physicist J. Robert Oppenheimer. The main laboratory was built on an isolated mesa at Los Alamos, New Mexico.
The first atomic bomb was tested at Alamogordo, New Mexico, on July 16, 1945.
See; Fission Bomb, Fusion Bomb, CP-1, Hiroshima, Nagasaki, Gun-Type Weapon, Implosion Weapon, Trinity Test.
MARV
The maneuvering reentry vehicle (MARV) is one of the latest developments in nuclear weapons delivery systems. MARVs are designed either to deliver a nuclear warhead with pinpoint accuracy, or to enable the warhead to avoid enemy detection and destruction through evasive maneuvers.
MARVs are expected to have an accuracy of 36.6 m (120 ft) after a flight of 1,609 km (1,000 mi). MARVs designed for evasive maneuvers employ such techniques as small steering rockets, internal weight shifting, and movable flaps or fins.
Mass Defect
The mass of an atom's nucleus is less than the sum of its constituents' masses. This difference is called the mass defect. Mass Number
See; Nucleus.
Megaton
This is approximately the amount of energy that would be released by the explosion of 1,000 kilotons (1,000,000 tons) of TNT.
Metallurgical Laboratory (Met. Lab)
Located at the University of Chicago, and led by Enrico Fermi, began work towards a controlled chain reaction.
Chicago Pile Number One or CP-1 went critical on December 2, 1942. They continued to work on further investigation of nuclear reactions.
The most vocal protest over the bomb's use came from the Met. Lab and was led by Leo Szilard.
See; CP-1.
MeV
A unit of energy. It is equivalent to 1.6 x 10-6 erg. Approximately 200 MeV of energy are produced for every nucleus that undergoes fission.
See; Electron Volt.
Micron
One-millionth of a meter.
Microsecond
One-millionth of a second.
Midgetman
Recommended for development by the bipartisan Presidential Commission on Strategic Forces, Midgetman is a new, small, highly mobile, single-warhead intercontinental ballistic missile. While the development and eventual deployment of Midgetman is expected to strengthen the land-based segment of the U.S. nuclear defense triad, it is also expected to influence or alter arms control negotiations. The single-warhead Midgetman would be fully effective only if limitations were set on the total number of warheads.
Mid-phase (or midcourse phase)
That part of the ballistic missile's flight when the re-entry vehicle and warhead travel freely through space outside the atmosphere. For an ICBM, this stage lasts about 20 minutes.
The MIKE Test
On November 1, 1952 a 10.4 megaton thermonuclear explosion, code-named MIKE, at Eniwetok Atoll demonstrated the release of energy from nuclear fusion. The apparatus was an experimental device, not a weapon, that had been constructed on the basis of the principles developed by Edward Teller and Stanislaw Ulam. The island of Elugelab in the Eniwetok Atoll on which the test was conducted, was completely vaporized.
See; Hydrogen Bomb.
Milling
A process in the uranium fuel cycle by which ore containing only a very small percentage of uranium oxide (U3O8) is converted into material containing a high percentage (80 percent) of U3O8 often referred to as yellowcake.
See; Yellowcake.
Mill Tailings
The leftover crushed rock after the uranium (yellowcake) has been removed from uranium ore.
See; Yellowcake.
Minuteman Missile
Minuteman was one of the earliest intercontinental ballistic missiles (ICBMs) developed by the United States. Of the three versions of Minuteman that have been deployed, only Minuteman III is still in service.
The Minuteman III is susceptible to reduction under the terms of the 1991 START treaty, although the treaty does not specify the actual weapons by name. Cuts in the number of Minuteman III warheads are, therefore, anticipated.
Mixed-oxide fuel (MOX)
A nuclear fuel, made from a mixture of plutonium dioxide and uranium dioxide, used in nuclear-power reactors as an alternative to uranium dioxide fuel.
Moderator
A component of nuclear reactors that slows neutrons, thereby increasing their chances of being absorbed by a fissile material. Natural water, heavy water and nuclear-grade graphite are the most common moderators.
Molecular laser isotope separation
A method of uranium enrichment that uses a laser to excite and ionize uranium hexafluoride molecules so they can be selectively removed.
Multiple Independently Targetable Reentry Vehicle (MIRV)
A package of two or more warheads which can be carried by a single ballistic missile but are deliverable to separate targets.
Mutual Assured Destruction (MAD)
The present situation in which the superpowers have the ability to inflict an unacceptable degree of damage upon each other even after absorbing a first strike; a condition which deters both sides from initiating hostilities.
MX Missile
The United States MX (MX-missile experimental) program has had a long and controversial history. Beginning in the 1960s, U.S. military experts anticipated growing improvement in the accuracy and number of Soviet missile systems, to the point where they would be able to attack and destroy the concrete underground silos within which the land-based U. S. intercontinental ballistic missiles (ICBMs) were housed. It therefore seemed necessary that new missiles should be deployed in such a way that they would be invulnerable to Soviet attack.

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