Wikijunior:How Things Work/Nuclear Bomb

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The B43 was a nuclear bomb made by the United states between 1961 and 1965.

Who invented it?[edit]

For many years, people had the idea that a nuclear bomb could be made. It took the Second World War to push scientists into turning the idea into reality. The United States of America, with British help, ran the Manhattan Project, under the leadership of Robert Oppenheimer, to design and build the first nuclear bomb.

What idea(s) and/or inventions had to be developed before it could be created?[edit]

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?[edit]

This diagram shows the different parts of a fission nuclear weapon.

The nuclear bomb works by releasing an enormous amount of energy, released as heat. The energy heats up the air around it, causing it to expand. This creates a shock-wave so strong that it can level entire cities. The heat also causes fires, but most notorious is the radioactivity that unleashes terrible suffering on those nearby, not killed by the shock-wave or the fires.

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 just 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.

In a fusion bomb, this 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 fission bomb going off and the hydrogen being blown apart, the temperature causes it to fuse into helium, releasing many times more energy.

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

How dangerous is it?[edit]

The city of Hiroshima before it had been destroyed by a nuclear bomb.
The city of Hiroshima after it had been destroyed by a nuclear bomb.

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.

Nagasaki, before (top) and after the atomic bomb.

What does it do?[edit]

The size of the explosion is dependent on the yield (strength) of the bomb, and that depends on its makeup. The energy release capability is so great that it is one of the strongest explosions mankind is capable of setting off. As any explosion it generates kinetic energy (force), that accounts also for the sound, heat and light. The explosion is so strong that a vacuum is created in its center, so that after the energy expansion the air is pulled back into the detonation point.

Depending on the bomb's yield (strength) 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 killing people. The heath causes a massive fireball that can burn people to death even if they are miles away from the point of explosion. The light may be several times stronger than that of the sun.

It can vary from a fairly small explosion from a "battlefield" nuclear weapon to an explosion big enough to destroy a very large city. But the major devastation and impact is that these bombs releases radiation that can poison and kill and cause genetic defects for many years afterwards.

How has it changed the world?[edit]

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.


Nuclear explosions that took place from 1945 up to 1998 in a time-lapse video mapNuclear explosions that took place from 1945 up to 1998 in a time-lapse video map, by Japanese artist Isao Hashimoto. Since the U.S unleashed the first nuclear bombs on Hiroshima and Nagasaki back in 1945 there have been a staggering 2056 nuclear tests recorded worldwide.
It took almost a year until the next major tests took place, but by the mid-50s and 60s, nuclear tests were being recorded across the globe on almost a monthly basis.

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 — the head of the USSR government, who had been allies during WWII — 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 — and of its pre-war Empire that was then ending — 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.

Who has "The bomb"?[edit]

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, 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.