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WEAPONS OF MASS DESTRUCTION
THE EVOLVING THREAT IN THE 21ST CENTURY
Others pages in this series:
Introduction
What are WMD?
Nuclear Weapons
Atomic History
Biological Weapons
Chemical Weapons
NUCLEAR WEAPONS
Prepared by Laura Reed, Security Studies Program, MIT, Cambridge, MA,
USA
Today, a handful of nations possess an inventory of about 30,000 nuclear
weapons, roughly half the number that existed at the height of the Cold
War. On average, these weapons each possess an explosive power 20 times
greater than the nuclear weapons that destroyed much of Hiroshima and
Nagasaki in Japan and killed roughly 250,000 people during World War
II. Since 1945, no nuclear weapon has been used in a conflict, even though
combatants—including nuclear weapons states—have fought approximately
100 wars in the intervening 60 years.
Meanwhile, though, because nuclear weapons have been a part of state
arsenals for more than half a century, there is a tendency among policymakers
toward tacit acceptance about these weapons that can, in itself, be dangerous.
Manhattan Project scientist Wolfgang Panofsky noted recently in a presentation
commemorating the 60th anniversary of the first nuclear test, that nuclear
weapons have increasingly come to be seen by some as: “symbols
of strength and prestige, and tools for diplomatic bargaining. Some decision
makers are even searching for new missions where conjectured circumstances
might give advantages to nuclear weapons over conventional munitions.” Such
efforts, risk endangering the longstanding taboo against the use of nuclear
weapons.
How Nuclear Weapons Work
Nuclear weapons, like conventional bombs, are designed to cause damage
through an explosion that releases a large amount of energy in a short
period of time. In conventional bombs, the explosion is created by a
chemical reaction, which involves the rearrangement of atoms to form
new molecules. In nuclear weapons, however, the explosion is created
by changing the atoms themselves, either by splitting them or fusing
them together to create new atoms.
The amount of energy released in such a nuclear reaction is enormous—many
orders of magnitude greater than that released in a chemical reaction
resulting in the rearrangement of molecules. The amount of energy available
within an atom is given by Einstein's famous formula E=mc2, where E =
energy, m = the mass and c = the speed of light. Thus the energy available
equals the mass multiplied by 9,000,000,000,000,000,000 (or the square
of the speed of light represented in meters per second). As a result,
a nuclear bomb using one kilogram of plutonium could have the same explosive
force as approximately 15 million kilograms of the conventional explosive
TNT.
As indicated above, there are two main types of nuclear weapons: fission
weapons and fusion weapons.
Fission weapons: In fission weapons, atoms are split. The core of a
fission bomb is made of either plutonium or highly enriched uranium.
Plutonium and uranium atoms are both heavy, meaning they have a large
number of protons and neutrons in the nucleus. During fission, when the
heavy nucleus splits into two smaller nuclei, extra neutrons are released.
If these neutrons are absorbed by other nuclei, they can, in turn, split,
also releasing neutrons and setting off what is known as a chain reaction.
Plutonium or highly enriched uranium are the only materials known that
can, under carefully designed circumstances, achieve such a devastatingly
powerful, self-sustaining fissile chain reaction.
Fusion weapons: In fusion weapons—often known colloquially as
hydrogen bombs— deuterium and tritium, two isotopes of hydrogen,
are fused together to create heavier atoms. This is the same reaction
that occurs in the center of the sun. Fusion can only happen at extremely
high temperatures and pressure. In a fusion weapon, such a state is created
by using a fission explosion (i.e. an atom bomb) to trigger the fusion
reaction. There is no theoretical limit to the explosive force of a fusion
weapon. Typically, fusion weapons are 10 to 100 times as explosive as
the fission bombs dropped on Hiroshima and Nagasaki.
Effects of Nuclear Weapons
To understand the effects of a nuclear weapon, it is important to realize
that a nuclear explosion produces several distinct forms of energy that
each has its own devastating set of consequences: blast, thermal radiation,
electromagnetic pulse, direct nuclear radiation, and fallout.
Blast: The rapid release of energy in an explosion creates a shock wave
equivalent to several thousand pounds of pressure per square inch (psi),
enough many times over to crush most objects on earth. By way of comparison,
brick houses and human lungs can be crushed at about 30 psi pressure
or less.
Thermal radiation: Thermal radiation includes heat and light. The heat
from a nuclear explosion is so intense that nearly all materials at the
center of the explosion (epicenter) are immediately vaporized. The thermal
radiation also creates a fireball which rapidly expands outward, consuming
oxygen and, combined with the blast effect, creating near total destruction
for some distance from the epicenter. Meanwhile, the light produced by
a nuclear explosion can be seen from hundreds of miles away. The radius
of the flash depends on the power of the weapon and the atmospheric weather
conditions. Generally, however, the light is so intense it can make sand
explode, blind people many miles away, burn shadows into concrete, ignite
flammable materials at large distances, and burn human skin.
Electromagnetic pulse: In addition to its other effects, a nuclear explosion
sends out an electromagnetic pulse, similar to the thermal pulse. Although
the electromagnetic pulse does not directly harm humans, it can increase
the devastation at the site of a nuclear explosion because it disables
all electrical devices in its path, including computers, communication
and medical devices.
Direct nuclear radiation: A nuclear explosion releases several forms
of radiation. Both gamma rays and neutrons easily penetrate solid objects
and can be deadly. Beta and alpha particles are generally less dangerous,
having much shorter ranges - several meters and several centimeters,
respectively. Alpha particles cannot penetrate human skin. If ingested,
however, alpha particles will cause the most damage to the human body.
Fallout: Fallout consists of large numbers of particles, from the earth,
buildings and other ground objects, which are propelled upward in the
blast and irradiated, mixing with the radioactive products of the explosion.
Some of this material will fall back to earth within a few minutes, and
radioactive fallout may continue its descent for about 24 hours. The
rising and descending debris forms the mushroom cloud that follows a
nuclear explosion. The distribution of fallout depends on the topography
of the land and weather conditions, especially the direction and speed
of winds. Radioactive fallout may travel and settle in areas hundreds
of miles from the explosion site.
Radioactive fallout may be the most insidious effect of a nuclear explosion
because the area of exposure to fallout is much wider and more unpredictable
than that of direct nuclear radiation. Its removal is a costly and dangerous
job. And, because there is no known way of neutralizing radioactive fallout,
it will remain dangerous until the individual radioactive particles have
decayed to such an extent that they no longer emit significant amounts
of radiation—a period that can last thousands of years.
Effects of Radiation on Humans
The effects of radiation on the human body vary, depending on the dosage
of radiation and whether exposure is slow and protracted or large and
instantaneous.
Radiation affects those cells in the human body that actively divide,
such as those found in hair, in the intestinal tract, in bone marrow,
and in the reproductive organs. A large, rapid dose of radiation causes
cell death, and effects are apparent within hours, days, or weeks. With
protracted exposure, however, cells can do some repair over the exposure
period. Radiation doses low enough to avoid cell damage can still induce
cellular changes that may be clinically detected sometime in the future,
and can potentially be passed on through mutated or defective genes.
The most serious delayed, long-term effect of radiation exposure is
a significantly increased incidence of leukemia and thyroid, lung, breast,
and bone cancers. The incidence of a particular type of cancer depends
on how the radiation exposure occurs. For example, uranium mine workers
display a high incidence of lung cancer from inhaling radioactive dust.
Workers who painted glow-in-the-dark radium onto watch faces at the turn
of the century licked their radioactive paintbrushes, leading to a high
incidence of bone cancer and radiation-induced anemia. There is also
a very high incidence of leukemia among Hiroshima survivors. These victims
also suffered from high incidences of cataracts and hair loss, as well
as increases in infertility and birth defects.
Note: The summaries above are compiled from the following sources where
additional information can be found.
For an introduction to atomic physics and nuclear weapons effects, see:
http://www.atomicarchive.com/sciencemenu.shtml
For information on nuclear weapons and weapons facilities worldwide,
see
The Nuclear Notebook, which includes updates of global nuclear arsenals
by Robert S. Norris and Hans Kristensen, suppoted by the Natural Resources
Defense Council (NRDC), an environmental NGO. http://www.thebulletin.org/nuclear_weapons_data/
For a description of types of nuclear weapons, their effects, and global
stockpiles, see:
http://www.nuclearfiles.org/menu/key-issues/nuclear-weapons/basics/index.htm
The Federation of American Scientists website offers a helpful overview
of nuclear weapons and technology. http://www.fas.org/nuke/intro/nuke/index.html
The Nuclear Weapon Archive, an offshoot of the Federation of the Atomic
Scientists website, provides information and technical data on the history
of nuclear weapons. http://nuclearweaponarchive.org/
For a discussion of the history of nuclear weapon-related accidents,
see the website of the Center for Defense Information, an independent
research organization based in Washington, D.C. http://www.cdi.org/Issues/NukeAccidents/accidents.htm
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