Since 1945, when the first nuclear bomb was exploded by the Manhattan Project team in the US, nuclear weapons have proliferated across the globe. Currently, the US has about 7,000 warheads and the nations of the former Soviet Union have approximately 6,000. There are enough nuclear weapons in the world to destroy all civilization as we know it. They are perhaps the most powerful forces that man has ever wielded. Other countries that possess known nuclear capabilities are the United Kingdom, France, the People's Republic of China, Pakistan, and India. When first developed, nuclear weapons were completely strategic weapons. That is, they were not designed to destroy enemy weaponry; they were designed to destroy entire cities. However, there are now small, tactical nuclear weapons in addition to the others. Besides how powerful a nuclear weapon is, there are other differences between them. They can be either a fusion or a fission device, and they can be dropped from an airplane, fired from an artillery gun, or attached to various types of rockets.

The Fission Bomb:

A fission bomb uses an uncontrolled nuclear fission chain reaction to release an enormous amount of energy in a small amount of time. Previously, you read about different ways that a fission chain reaction is controlled in a nuclear reactor. In a bomb all those safeguards are removed. There are no control rods and when uranium is used as the fuel, it is much more enriched than the 4% 235U in nuclear fuel rods. This means that there is less 238U and thus less neutrons are captured.

The fissile material (plutonium or uranium) in the bomb is usually surrounded by conventional explosives (non-nuclear). When the bomb is detonated, the conventional explosives are ignited. These explosives are designed to blow inwards, crushing the fissile material they surround. This compaction of the uranium or plutonium increases the chance that a stray neutron will strike a nucleus, inducing fission and the result runaway chain reaction. Once the nuclear material is compressed to the point of criticality (able to undergo a runaway nuclear reaction), a neutron "gun" fires. This "gun" shoots extra neutrons into the critical mass of fuel. This adds a lot of extra neutrons, which increase the chain reaction. As the chain reaction begins to grow exponentially, the inside of the bomb gets hotter and hotter. At a certain point, the pressure and heat are too intense for the casing, and it is ripped apart. Then the bomb explodes into the surrounding area and atmosphere, releasing fall-out and radioactivity into the environment. Additionally, the shock wave from the blast can level immense areas around the bomb. However, this area depends on the strength of the bomb. When the bomb explodes, the particles that made up the bomb are vaporized and enter the atmosphere as a fall-out cloud. The radioactive fall-out that is released consists of the fission products and the transuranic neutron-capture products, just like those in spent fuel rods. The difference is that the reaction in a bomb occurs at a much, much faster rate than that in a power plant.

Thermonuclear Fusion Bombs:

Fusion bombs have two main stages. These are called the "primary" and the "secondary". The primary reaction is a regular fission chain reaction. The radiation from this reaction is used to heat the interior of the bomb to temperatures where a fusion reaction can be sustained. Also, the neutrons produced from the fission reactions are used in the secondary (fusion) part of the reaction. The secondary is composed of lithium-deteuride (deuteride is basically deuterium, which is 2H). The lithium deteuride, under intense heat, splits apart into lithium (6Li) and deuterium ions. The neutrons produced from the primary (fission) reaction react with the 6Li to produce 4He and 3H. This reaction can be expressed in the following equation:

1 neutron + 6Li 4He + 3H
3H + 2H 4He + 1 neutron

A thermonuclear fusion bomb is generally a lot more powerful than a fission bomb. Interestingly, the harmful fall-out from a fusion bomb is generated mostly from the products of the primary (fission) reaction. These are the fission products and the transuranic products, just like in the fall-out of a standard fission bomb.

Aftermath:

If all the nuclear weapons in the world were used, then all of humanity would most like be destroyed. This is for several reasons. Firstly, most major cities would be destroyed by incoming warheads. However, this would leave some areas untouched. Thes e areas would most likely be reached by radioactive fall-out blown by the wind. These would be the immediate repurcussions.

Later, the world would go into what is called "Nuclear Winter". Global temperatures would drop significantly, as well as the amount of sunlight received by the earth. This is very similar to what is believed happened to the dinosaurs. It is believed th at a large asteroid collided with the earth, and stirred up a lot of dust into the atmosphere. This blotted out the sun, and plants died. With very few plants to eat, the dinosaurs (and many other animals) went extinct. Nuclear winter would be a lot like this. The only difference is that there the dust would be raised up by impacting nuclear warheads and their explosions. Additionally, the dust would be radioactive. The combination of radioactivity, lack of food, and lowering temperatures cause a Nuclear Holocaust, with the chances of humans surviving it very low.

Quiz time (feel free to re-look at the above material while completing the quiz):