Wikijunior:How Things Work/Nuclear Bomb

Who invented it?
When Enrico Fermi and colleagues studied the results of bombarding uranium with neutrons in 1934, people started to realize that nuclear energy could be used to create a bomb &mdash; any fast energy release can be turned into a bomb. It took the Second World War to push scientists into actively pursuing the idea into reality. The Germans, under the rule of Hitler made several initial investigations into the field and were on the right path but never seemed to reach the ability to create a bomb. The allies knew about the Germans' efforts, and actively sabotaged and undermined them. This also prompted the United States of America, together with Britain and Canada and deliberately without the then Soviet Union ally, to create the Manhattan Project, under the leadership of Robert Oppenheimer, to specifically design and build the first nuclear bomb.

These independent efforts lead by the US were spied on by the Soviets almost from the start, it could be stated that this was the initial step for the future cold war, as the bomb would shift the geopolitical power balance. Of notice is that the Soviets had from the start been making large contributions to this specific field of physics and to a large degree managed to develop their own bomb, using only the spied data from the Manhattan Project as a verification and simplification tool to archive their goal.

What idea(s) and/or inventions had to be developed before it could be created?
A tentative listing would certainly include Fire, Tool Use, Science, Mechanics, Metallurgy, Mineralogy, Chemistry, Explosives, Mathematics (Geometry and Algebra), Physics, Radiology, Engineering, Economics, Politics and the Nation State, "Modern" Warfare (Post-Industrial Age).

The binding energy, which is how much energy is stored in the heavy nuclei such as uranium and plutonium, had to be discovered. The process of creating material capable of reaching critical mass is very difficult and represents a significant engineering challenge.

How does it work?
There are two types of nuclear bombs, fission bombs and fusion bombs. Fission means to break apart and fusion to merge.

The fission bomb works on the principle that it takes energy to put together a nucleus with many protons and neutrons. Sort of like rolling a heavy cart up a hill. Splitting the nucleus up again then releases some of that energy. Some atoms have unstable nuclei which means that they tend to break apart with little or no nudging.

You may have heard of uranium and plutonium and that they are radioactive elements. These two have such unstable nuclei which causes their radioactivity. When a nucleus breaks into two smaller nuclei, a couple of neutrons shoot out. This is the radiation. Naturally occurring uranium and plutonium have atoms constantly undergoing radioactive decay. These are spaced sufficiently far apart so that the neutrons rarely bump into other unstable nuclei.

When a neutron, however, does hit an unstable nucleus, just like someone bumping into a cart at the top of a hill, it causes that nucleus to break apart and send out another couple of neutrons. By increasing the concentration of these unstable atoms, the probability that a neutron from one decay causes another one increases. The concentration where the reaction sustains itself is called critical mass and the reaction then called a chain reaction.

With each step of the reaction, energy is released and another step or two is started, and so an avalanche of reactions and energy release continues until the fissile (unstable) material is spent.

Actually, any nuclei heavier than that of iron (Fe56 which has 56 nucleons, to be precise) will release energy when broken apart. Lighter nuclei on the other hand usually release energy when they merge, or fuse. The most energy is released when two hydrogen nuclei fuse into a helium nucleus. Unlike the radioactive elements, getting the two helium nuclei to merge already takes a good deal of energy. Sticking with the analogy of the cart, it is like it's sitting in a hole at the top of the hill and needs a considerable push before rolling down.

The fusion bomb initial energy is created by heating the hydrogen up to a tremendous temperature with a fission bomb as the first stage. In the split second between the initiating fission going off and the hydrogen being blown apart, the temperature causes it to fuse into helium, releasing many times more energy.

The special case of a dirty "nuclear" bomb
A dirty bomb can also be loosely defined as a nuclear bomb but does not require weapons graded fissionable material, it has more in common with chemical weapons. It uses a conventional explosive system to spread radioactive contaminants across an area. No bomb of this type has so far been used. Its effects would be similar to what occurs in large atmospheric nuclear disasters, like the one of Chernobyl.

How dangerous is it?
The bomb in its stored state isn't very dangerous, as it takes some effort to set it off. Once detonated, the explosion is extremely dangerous. Even those that survive the blast and the fires will be subject to varying levels of radiation (mostly depending on how close they were to the bomb) that can cause death, cancer, leukemia, or harm to reproductive organs resulting in a higher level of birth defects, or even complete sterility.

Only two nuclear bombs have been used in warfare. Toward the end of World War II, the United States dropped bombs on the Japanese cities of Hiroshima and Nagasaki. The death-toll from these bombings was in the hundreds of thousands.

In Hiroshima, the immediate effects of the blast killed about 70,000 people. In the aftermath, between 90,000 to 140,000 more people died from burns, radiation, and related disease.

What does it do?
The nuclear bomb explosion, like any explosion, releases an enormous amount of energy in the form of heat and kinetic energy (force), that accounts also for the sound, heat and light. The size of an explosion is dependent on the yield (strength) of the bomb, and that depends on its makeup. It can vary from a fairly small explosion from a "battlefield" nuclear weapon to an explosion big enough to destroy a very large city. The energy release capability of nuclear devices is so great that it is one of the strongest explosions mankind is capable of setting off.

The energy released from a nuclear weapon exploded in the air is split four ways:


 * Blast—40-50% of total energy
 * Thermal radiation—30-50% of total energy
 * Ionizing radiation—5% of total energy
 * Residual radiation—5-10% of total energy

Depending on the bomb's yield and on the environment of the blast. It can generate ground shock waves that are even stronger than the strongest naturally occurring earthquake, that energy and the sound waves alone can reach considerable distances and alone flatten buildings and kill people. The explosion is so strong that a vacuum is created in its center; so that after the energy expansion dissipates the air is pulled back into the detonation point.

The huge force generates not only a light that may be several times stronger than that of the sun (due to the high energy collision of matter) but will push away the air around, forcing it to expand, this acceleration creates a shock-wave so strong that is able to level entire cities by itself. The kinetic energy will also be turned into heat, creating a massive fireball. The heat alone will burn people to death and cause fires miles away from the point of explosion. But the major devastation and impact is the radiation that unleashes terrible suffering not only on those nearby that may miraculously survive but also those living at range of the ensuing radioactive contamination, poisoning and causing genetic defects for several generations (lifetimes).

Unlike any other type of bomb that have simply a tactical destructive purpose of life or installations, the nuclear arsenal has so far been solely been under the control of nation states and primarily served as a deterrent and political tool to avoid prolonged and open conflict. Note that special attention is given to the delivery system of the devices. From a "crude" bomb that was intended to be dropped from a plane it evolved into technologically advanced payload for intercontinental missiles, since the first shot will be strategically the deciding factor of who suffers less form the outcome of a nuclear conflict, where there are no victors.

How has it changed the world?
The nuclear bomb is one of the most destructive weapons ever created. But it was not its development that changed the world but the realization that nations would consider using such weapons. Toward the end of the second world war, the United States dropped two nuclear bombs on the Japanese cities of Hiroshima and Nagasaki. This was done mainly to make Japan surrender sooner, so the US would not have to invade Japan itself and the USSR would not start to invade the Japanese territories. The reckless destruction and immediate and long-term effects of the bombings have created a strong sentiment against the use of nuclear weapons.

After its use against Japan, there was a major shift in world political power towards the US, that permitted the US to block, even dismiss, previous understandings with Stalin &mdash; the head of the USSR government, who had been allies during WWII &mdash; about territory and areas of influence. This new unbalance was the start for the nuclear arms race and greatly increasing nuclear tests with drastic effects on the environment.

Soon after the end of WWII, the US, with support of the previous major power and principal ally, the United Kingdom &mdash; and of its pre-war Empire that was then ending &mdash; took steps to block the advance of the Soviets (USSR) expansion into Europe. This led, for decades, to a gridlocked power struggle known as the Cold War. Both sides had enough nuclear bombs to completely destroy each other, which would also do terrible damage to the entire world population. This gave everyone a very strong reason to avoid starting a war, creating a strategy called mutually assured destruction (MAD), which influenced world politics during the Cold War and defined the balance between Super-powers.

Nuclear De-escalation
The principal goal of nuclear de-escalation is intended to preserve a balance of power between all opposing poles of the geopolitical nuclear table, like the United States versus Russia or Pakistan versus India and to a lesser degree China or even in a near future Israel, Iran and Saudi Arabia. This is also the central point of the continual ransom game North Korea plays with the US, South Korea and Japan.

While treaties alone saves those nations resources in a continual power struggle for world or regional influence where economic and technology might then takes prominence over the capability of mass production of nuclear weapons. At the same time this mutually agreed strategy has its flaws or is clearly skewed to favour one side, for example with the ban on nuclear tests the nation that has a better technological capability to advance nuclear armament through simulations and related technologies like delivery systems (distance, stealth and miniaturization) and improved detonation systems gains an advantage, this and the creation of abilities to intercept and disable intercontinental delivery vehicles puts pressure in having not only more weapons but develop capabilities to influence (social-economically) the opposition and be able to detect and monitor nuclear weapons stockpiles and movements.

Who has "The bomb"?
The United States, United Kingdom, France, India, Pakistan, Russia, North-Korea, and China all admit that they have a nuclear arsenal. Israel does not admit it but is believed to also have nuclear weapons; this is also supported by an unclaimed test done near South-Africa/Antarctica (the Vela Incident), and Israel having bought elements for nuclear weapons.

The South African government dismantled all of its nuclear weapons in 1990, the first nation in the world to voluntarily give up all nuclear arms it had developed itself.

There are many other states that may have nuclear weapons created in secret or maintained by some sort of accord with a nuclear nation. For example, by November 2009, Belgium, Germany, Italy, the Netherlands and Turkey were still hosting US nuclear weapons as part of NATO.