Glossary

Safety Experiment
An experiment designed to confirm that a nuclear explosion would not occur in case of an accidental detonation of the chemical explosive associated with the device.
Scaling Law
A mathematical relationship which permits the effects of a nuclear (or atomic) explosion of given energy yield to be determined as a function of distance from the explosion (or from ground zero), provided the corresponding effect is known as a function of distance for a reference explosion (e.g., of 1-kiloton energy yield).
See; Blast scaling laws, Cube root law.
Seabed Treaty
Prohibits the placement of nuclear weapons or any other weapons of mass destruction on the seabed, the ocean floor, and in the subsoil of the ocean floor beyond a signatory's 12-miles coastal zone.
Sea Launched Cruise Missile (SLCM)
See; Cruise Missile.
Secondary
The component of a nuclear weapon that contains elements needed to initiate the fusion reaction in a thermonuclear explosion.
See; Fusion, Fusion Bomb.
Seismic Calibration
A test conducted to evaluate seismic effects of an underground explosion.
Seismic Monitoring
Seismic monitoring offers virtually the only technique for determining occurrence and magnitude of underground tests. Seismic techniques have been extensively developed, and all treaties rely heavily on an array of detection stations.
Shaft
A type of underground test in which a nuclear device exploded at the bottom of a drilled or mined vertical hole. Some safety tests were set off at the bottom of unstemmed drilled holes.
Shock Wave
A continuously propagated pressure wave in the surrounding medium which may be air, water, or earth, initiated by the expansion of hot gases produced by a nuclear explosion.
See; Overpressure.
Sievert (Sv)
The modern unit of radiation does, incorporating quality factors for the biological effectiveness of different types of ionizing radiation (implying that alpha particles are 20 times more dangerous than X-rays depositing the same amount of energy in tissues).
See; Ionizing Radiation.
Silo
Hardened underground facility for housing and launching a ballistic missile and designed to provide pre-launch protection
Simultaneous
Two or more underground nuclear explosions (detonations) conducted within an area delineated by a circle having a diameter of 2 kilometers (1.24 miles) and conducted within a total period of time that did not exceed 0.1 second.
Single Integrated Operations Plan
Single Integrated Operational Plan (or SIOP) is a blueprint that tells how American nuclear weapons would be used in the event of war.
Site W: Hanford
To produce the needed plutonium, three reactors were constructed at Hanford, Washington. The reactors eventually produced several hundred grams of plutonium a day.
The plutonium for the Trinity and Fat Man bombs were produced here. Hanford continues to produce plutonium for the United States nuclear weapons.
See; Manhattan Project, Trinity Test.
Site X: Oakridge
Oakridge was designed specifically for the separation of uranium. The separation was pursued in two methods; electromagnetic and gas diffusion.
The uranium used in the Hiroshima bomb came from the Oak Ridge plant.
See; Manhattan Project.
Site Y: Los Alamos
Built atop a mesa in northern New Mexico, this was where the atomic bombs were designed and tested. Los Alamos continues to develop nuclear weapons.
See; Manhattan Project.
Slant Range
The distance from an explosion to an observer is called the slant range. For a burst height, h, and a distance, d, from ground zero to a given point, the slant range, D, is from the Pythagorean theorem.
Southeast Asian Nuclear-Weapon-Free-Zone
See; Treaty of Bangkok.
South Pacific Nuclear-Weapon-Free-Zone
See; Treaty of Rarotonga.
Special Engineering Detachment (SED)
An Army program that identified enlisted personnel with technical skills, such as machining, or who had some science education beyond high school. Those identified were organized into the Special Engineer Detachment, or SED. SED personnel began arriving at Los Alamos in October 1943. By August 1945, 1800 SED personnel worked at Los Alamos. These troops worked in all areas and activities of the Laboratory, including the Trinity Test, and were involved in overseas operations on Tinian.
Spent Fuel
Uranium fuel that has been used and then removed from the reactor.
Spontaneous Fission
The natural decay of a nucleus by splitting apart (fissioning).
See; Fission.
Star Wars
See; Strategic Defense Initiative.
Strategic Air Command (SAC)
The Strategic Air Command (SAC), was formed in 1946 as the arm of the U.S. Air Force that controls its long-range nuclear strike force. SAC headquarters were at Offutt Air Force Base, Nebraska. SAC was deactivated on June 1, 1992 and replaced with STRATCOM.
See; Strategic Command (STRATCOM).
Strategic Command (STRATCOM)
Strategic Command (STRATCOM) is headquartered at Offutt Air Force Base, Nebraska. The command is responsible for both early warning of and defense against missile attack and long-range conventional attacks. The command is charged with deterring and defending against the proliferation of weapons of mass destruction. It replaces Strategic Air Command (SAC) in 1992.
Strategic Arms Limitations Talks (SALT I & II)
Strategic Arms Limitations Talks between the Soviet Union and the United State were aimed at limiting missile systems and other strategic armaments. The first round of talks (SALT I) was held from 1969-1972, and the second from 1972-1979. SALT I concluded on May 20, 1971, when the ABM Treaty and the Interim Agreement limiting strategic offensive arms were signed. The SALT II Treaty was signed but was not ratified by either country.
Strategic Arms Reduction Talks (START I & II)
This term refers to the negotiations between the United States and the Soviet Union/Russian Federation to limit and reduce the numbers of strategic offensive nuclear weapons in each country's nuclear arsenal. The talks resulted in the 1991 START I Treaty, and the 1993 START II Treaty. START I was originally negotiated between the United States and the Soviet Union, and now applies to the United States, Russian Federation, Belarus, Kazakhstan and Ukraine. Belarus, Kazakhstan, and Ukraine have all renounced their possession of nuclear weapons under the 1992 Lisbon Protocol to START I. START II, which calls for further reductions in the United States and Russia has been ratified by the two countries, but has not yet entered into force.
See; Lisbon Protocol.
Strategic Defense Initiative (SDI)
The Strategic Defense Initiative (SDI) is a U.S. research and development program designed to create an effective defense against nuclear-missile attack, initiated by President Reagan in 1983. As envisioned, the system uses a "layered" defense in which enemy missiles would come under continuous attack from the time they are launched to just before they reach their targets, a total of about 30 minutes.
See; Ballistic Missile Defense.
Strategic nuclear warheads
Warheads placed on long-range delivery systems, on land-based Intercontinental ballistic missiles (ICBMs), submarine-launched ballistic missiles (SLBMs), and long-range bombers.
See; ICBMs, SLBMs.
Subcritical mass
Having a mass of fissionable material that is less than that needed for a chain reaction.
See; Critical Mass.
Subcritical tests
Tests that are used to gather information about nuclear warhead design and performance. Although sub-critical tests use some fissile materials, the tests do not produce a lead to any release of radioactivity.
Submarine-launched ballistic missile (SLBM)
A ballistic missile deployed on a submarine.
See; Ballistic Missile.
Subsidence Crater
A depression that may form at the ground surface following an underground detonation. At the end of the dynamic phase of cavity growth, a pressurized standing cavity is present. As the cavity pressure and temperature decrease, the roof of the cavity becomes unstable and falls into the cavity. The top of the so-called “chimney,” now formed above the cavity, continues to fall into the void. A phenomenon known as “bulking” results in the fallen material having decreased density from its normal state, hence increased volume. If the bulking fills the chimney, collapse stops without reaching the surface. Such a subsurface collapse can also be caused by the chimney's intercepting a high-strength geologic structure. When the chimney reached the surface, a subsidence crater was formed. The size of the subsidence crater depends on the yield of the device, the depth of emplacement, and the geological characteristics of the surrounding soil.

A throw-out crater (see crater) is formed by a totally different mechanism than a subsidence crater.
Surface
A type of atmospheric test in which a nuclear device was placed on or close to the earth's surface, but no more than 10 ft off the ground.
Surface elevation
The vertical distance from mean sea level to a point on the earth’s surface; generally refers to the surface ground zero of a nuclear device test/detonation.
Supercritical
A term used to describe the state of a given fission system when the quantity of fissionable material is greater than the critical mass under existing conditions. A highly supercritical system is essential for the production of energy at a very rapid rate so that an explosion may occur.
See; Critical Mass.