Disaster was avoided when the United States agreed to an offer made by Soviet leader Nikita Khrushchev to remove the Cuban missiles in exchange for the United States promising not to invade Cuba. Many Americans became concerned about the health and environmental effects of nuclear fallout—the radiation left in the environment after a nuclear blast—in the wake of World War II and after extensive nuclear weapons testing in the Pacific during the s and s.
The antinuclear movement emerged as a social movement in at the height of the Cold War. During Women Strike for Peace demonstrations on November 1, co-organized by activist Bella Abzug , roughly 50, women marched in 60 cities in the United States to demonstrate against nuclear weapons.
The antinuclear movement captured national attention again in the s and s with high profile protests against nuclear reactors after the Three Mile Island accident—a nuclear meltdown at a Pennsylvania power plant in In , a million people marched in New York City protesting nuclear weapons and urging an end to the Cold War nuclear arms race. It was one of the largest political protests in United States history. The United States and Soviet Union took the lead in negotiating an international agreement to halt the further spread of nuclear weapons in Nuclear weapons states included the five countries that were known to possess nuclear weapons at the time—the United States, the U.
According to the treaty, nuclear weapons states agreed not to use nuclear weapons or help non-nuclear states acquire nuclear weapons. They also agreed to gradually reduce their stockpiles of nuclear weapons with the eventual goal of total disarmament.
Non-nuclear weapons states agreed not to acquire or develop nuclear weapons. When the Soviet Union collapsed in the early s, there were still thousands of nuclear weapons scattered across Eastern Europe and Central Asia. Many of the weapons were located in Belarus, Kazakhstan and Ukraine. These weapons were deactivated and returned to Russia. Some countries wanted the option of developing their own nuclear weapons arsenal and never signed the NPT.
India was the first country outside of the NPT to test a nuclear weapon in Pakistan has a known nuclear weapons program. Israel is widely believed to possess nuclear weapons, though has never officially confirmed or denied the existence of a nuclear weapons program.
South Sudan is not known or believed to possess nuclear weapons. North Korea initially signed the NPT treaty, but announced its withdrawal from the agreement in Of the energy produced, 93 percent is the kinetic energy of the charged fission fragments flying away from each other, mutually repelled by the positive charge of their protons. This initial kinetic energy imparts an initial speed of about 12, kilometers per second.
Here, their motion is converted into X-ray heat, a process which takes about a millionth of a second. By this time, the material in the core and tamper of the bomb is several meters in diameter and has been converted to plasma at a temperature of tens of millions of degrees.
This X-ray energy produces the blast and fire which are normally the purpose of a nuclear explosion. Boundless vets and curates high-quality, openly licensed content from around the Internet. This particular resource used the following sources:. Skip to main content. To detonate the bomb, the explosives were ignited, releasing a shock wave that compressed the inner plutonium and led to its explosion.
Browse our collection of oral histories with workers, families, service members, and more about their experiences in the Manhattan Project. Skip to main content. Science Behind the Atom Bomb. History Page Type:. Thursday, June 5, Fission The isotopes uranium and plutonium were selected by the atomic scientists because they readily undergo fission. Criticality In order to detonate an atomic weapon, you need a critical mass of fissionable material.
The Difference Between the Bombs Little Boy and Fat Man utilized different elements and completely separate methods of construction in order to function as nuclear weapons. Fat Man Powered by plutonium , Fat Man could not use the same gun-type design that allowed Little Boy to explode effectively - the form of plutonium collected from the nuclear reactors at Hanford, WA for the bomb would not allow for this strategy. Atomic Glossary Atom : building blocks of matter; made up of a small, dense nucleus surrounded by a cloud of electrons negatively-charged particles Nucleus : makes up the center of the atom; consists of a number of positively-charged protons and a neutral no charge neutrons.
An atom is classified by the number of protons and neutrons in its nucleus. The number of protons determines which chemical element the atom is e. If the circle of marbles are spread too far apart -- subcritical mass -- a smaller chain reaction will occur when the "neutron marble" hits the center.
If the marbles are placed closer together in the circle -- critical mass -- there is a higher chance a big chain reaction will take place. Keeping the fuel in separate subcritical masses leads to design challenges that must be solved for a fission bomb to function properly.
The first challenge, of course, is bringing the subcritical masses together to form a supercritical mass, which will provide more than enough neutrons to sustain a fission reaction at the time of detonation.
Bomb designers came up with two solutions, which we'll cover in the next section. Next, free neutrons must be introduced into the supercritical mass to start the fission. Neutrons are introduced by making a neutron generator. This generator is a small pellet of polonium and beryllium, separated by foil within the fissionable fuel core.
In this generator:. Finally, the design must allow as much of the material as possible to be fissioned before the bomb explodes. This is accomplished by confining the fission reaction within a dense material called a tamper , which is usually made of uranium The tamper gets heated and expanded by the fission core. This expansion of the tamper exerts pressure back on the fission core and slows the core's expansion.
The tamper also reflects neutrons back into the fission core, increasing the efficiency of the fission reaction. The simplest way to bring the subcritical masses together is to make a gun that fires one mass into the other. A sphere of U is made around the neutron generator and a small bullet of U is removed.
The bullet is placed at the one end of a long tube with explosives behind it, while the sphere is placed at the other end. A barometric-pressure sensor determines the appropriate altitude for detonation and triggers the following sequence of events:. Little Boy , the bomb dropped on Hiroshima, was this type of bomb and had a That is, 1.
The second way to create a supercritical mass requires compressing the subcritical masses together into a sphere by implosion. Fat Man , the bomb dropped on Nagasaki, was one of these so-called implosion-triggered bombs.
It wasn't easy to build. Early bomb designers faced several problems, particularly how to control and direct the shock wave uniformly across the sphere. Their solution was to create an implosion device consisting of a sphere of U to act as the tamper and a plutonium core surrounded by high explosives. When the bomb was detonated, it had a kiloton yield with an efficiency of 17 percent. This is what happened:. Designers were able to improve the basic implosion-triggered design.
In , American physicist Edward Teller invented the concept of boosting. Boosting refers to a process whereby fusion reactions are used to create neutrons, which are then used to induce fission reactions at a higher rate. It took another eight years before the first test confirmed the validity of boosting, but once the proof came, it became a popular design. In the years that followed, almost 90 percent of nuclear bombs built in America used the boost design.
Of course, fusion reactions can be used as the primary source of energy in a nuclear weapon, too. In the next section, we'll look at the inner workings of fusion bombs. Fission bombs worked, but they weren't very efficient. It didn't take scientists long to wonder if the opposite nuclear process -- fusion -- might work better. Fusion occurs when the nuclei of two atoms combine to form a single heavier atom.
At extremely high temperatures, the nuclei of hydrogen isotopes deuterium and tritium can readily fuse, releasing enormous amounts of energy in the process. Weapons that take advantage of this process are known as fusion bombs , thermonuclear bombs or hydrogen bombs. Fusion bombs have higher kiloton yields and greater efficiencies than fission bombs, but they present some problems that must be solved:.
Scientists overcome the first problem by using lithium-deuterate, a solid compound that doesn't undergo radioactive decay at normal temperature, as the principal thermonuclear material. To overcome the tritium problem, bomb designers rely on a fission reaction to produce tritium from lithium.
The fission reaction also solves the final problem. The majority of radiation given off in a fission reaction is X-rays , and these X-rays provide the high temperatures and pressures necessary to initiate fusion.
So, a fusion bomb has a two-stage design -- a primary fission or boosted-fission component and a secondary fusion component. To understand this bomb design, imagine that within a bomb casing you have an implosion fission bomb and a cylinder casing of uranium tamper. Within the tamper is the lithium deuteride fuel and a hollow rod of plutonium in the center of the cylinder. Separating the cylinder from the implosion bomb is a shield of uranium and plastic foam that fills the remaining spaces in the bomb casing.
Detonation of the bomb causes the following sequence of events:. All of these events happen in about billionths of a second billionths of a second for the fission bomb implosion, 50 billionths of a second for the fusion events.
The result is an immense explosion with a 10,kiloton yield -- times more powerful than the Little Boy explosion. It's one thing to build a nuclear bomb. It's another thing entirely to deliver the weapon to its intended target and detonate it successfully.
This was especially true of the first bombs built by scientists at the end of World War II. Writing in a issue of Scientific American, Philip Morrison, a member of the Manhattan Project , said this about the early weapons: "All three bombs of -- the [Trinity] test bomb and the two bombs dropped on Japan -- were more nearly improvised pieces of complex laboratory equipment than they were reliable weaponry.
The delivery of those bombs to their final destination was improvised almost as much as their design and construction.
The components of the Fat Man bomb, carried by three modified Bs, arrived on August 2. A team of 60 scientists flew from Los Alamos, N. The Little Boy bomb -- weighing 9, pounds 4, kilograms and measuring 10 feet 3 meters from nose to tail -- was ready first. Paul Tibbets. The plane made the mile 1,kilometer trip to Japan and dropped the bomb into the air above Hiroshima, where it detonated at exactly a.
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