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FACTS ABOUT NUCLEAR WEAPONS |
We will take the word weapon to mean an explosive weapon, such as a bomb, the warhead of a missile or an artillery shell. All weapons contain explosive material which explode when suitably triggered. In conventional weapons, the explosive material is something that can undergo some chemical reaction that proceeds very fast and releases a lot of energy. Basically it can `burn' so fast that it explodes. The first explosive material used in weapons was gunpowder, nowadays more powerful explosives like TNT and RDX are used.
The explosive material in a nuclear weapon can undergo a nuclear reaction at a very fast rate. What a nuclear reaction is and why it releases so much energy is explained later.
An important difference between a chemical and a nuclear reaction is that the latter releases about a million times more energy than a chemical reaction. This difference makes nuclear weapons much more powerful than conventional ones.
One measure of the power of a weapon is given by the total amount of energy released in the explosion. This is called the yield of the weapon. The yield of nuclear weapons is usually expressed in terms of the equivalent amount of TNT which would release the same amount of energy. So a single `small' nuclear weapon whose yield is ten kilotons releases the same amount of energy as ten kilotons, i.e. 10,000,000 (one crore) kilograms of TNT.
To get a better idea of what these numbers mean, let us see how many conventional bombs would release the same amount of energy as one such small nuclear bomb. A 10 kiloton nuclear bomb weighs about 500 kg whereas a conventional bomb of the same weight contains about 250 kg of explosives. So a single small nuclear bomb releases as much energy as about 40,000 conventional bombs. The explosion of such a bomb is then like forty thousand conventional bombs exploding simultaneously at the same point.
Nuclear weapons are tremendously more powerful than conventional ones. They cause death and destruction on a much larger scale. They are indeed weapons of mass destruction.
The second major difference is that a nuclear explosion produces large amounts of ``radioactive" material that give out deadly rays of nuclear radiation. (This is also called the fallout.) A large dose of radiation can kill a human instantly. Exposure to a somewhat smaller amount can have even worse consequences. It can cause severe illness leading to slow death after days or even years of suffering. Radiation can cause genetic damage leading to babies being born deformed. It contaminates large areas of land, making it useless for agriculture for years or even decades. These aspects of nuclear weapons thus introduce a new dimension of horror. The poisoning of humans and their environment by radiation makes the process of recovering from a nuclear attack a long and painful one.
These are the reasons why a large section of informed and sensible people in the world consider nuclear weapons to be unacceptable, much more so than biological and chemical weapons, which are already banned by international agreement.
Two types of nuclear reactions are used in nuclear weapons. The nuclei of some heavy elements like uranium or plutonium can split into two roughly equal sized nuclei with the release of energy. Such a process is known as nuclear fission. On the other hand, two light nuclei can undergo nuclear fusion to combine and form a single nucleus, again with the release of energy. These reactions are explained in detail later. All nuclear weapons use fission and fusion reactions in different combinations.
From the point of view of military usage, the weapons fall into two classes. The first are called tactical weapons. These are meant to be used in the battlefield against military formations and are typically low-yield weapons. The second class are called strategic weapons. These are high-yield weapons designed to kill civilian populations in cities. The different types of weapons that have been built or thought of are described below.
Weapons in which only the fission reaction takes place are called pure fission weapons or simply fission weapons. Such were the bombs dropped on Hiroshima and Nagasaki. These are the simplest nuclear weapons to design and build. They form the basis for developing other types of weapons. Their yield can range from a few tons to about a few hundred kilotons. They can be both tactical and strategic weapons. The largest pure fission weapon tested is believed to be a 500 kiloton bomb called Mk-18 which was tested by the USA on the 15th November 1952.
The efficiency of a fission weapon can be dramatically increased by introducing a small amount of material that can undergo fusion. Such weapons are called boosted fission weapons. In boosted weapons, the fission reaction takes place first and produces the required temperatures and densities for the fusion reaction. The fusion in turn accelerates the fission reaction. The fusion only serves to help the fission process go faster and makes the weapon more `efficient'. It contributes to only about 1% of the yield. Since boosted fission weapons are more efficient than pure fission weapons, they can be made lighter for the same yield. So most of the strategic fission weapons deployed today are boosted fission weapons.
Thermonuclear weapons, also called hydrogen bombs, get most of their yield from the fusion reaction. As in the case of boosted fission weapons, they require a fission explosion (called the primary stage) to trigger the fusion (the secondary stage). However, unlike the boosted weapons, thermonuclear weapons contain a substantial amount of fusion fuel and most of their yield comes from fusion. These are the most powerful nuclear weapons, often with yields of a few megatons (a megaton is a million tons). A third fission stage can also be added to produce very high yield weapons. The most powerful nuclear weapon to have been tested so far is the Tsar Bomba, a 50 megaton three-stage weapon exploded by the USSR on 30th October, 1961. However it is not necessary for a thermonuclear weapon to have such high yields. The B61 (Mk-61) class of tactical thermonuclear weapons deployed by the USA have yields which can be adjusted to be as small as 0.3 kilotons (300 tons).
Enhanced radiation weapons, also called neutron bombs, are small thermonuclear weapons which are designed to produce intense nuclear radiation. These are tactical weapons designed to kill soldiers protected by armour (for example, inside tanks). The radiation produced by the neutron bombs can easily penetrate the armour of tanks and kill the humans inside.
Salted nuclear weapons, or cobalt bombs, are thermonuclear weapons which are designed to produce a large amount of long lasting radioactive fallout. This would result in large scale radioactive contamination of the area they are dropped in. The fallout from salted weapons is much more intense and lasts much longer than from unsalted weapons. The long term effects of such weapons would therefore be much worse. These weapons are called `Doomsday Devices' since they could possibly kill everyone on earth. Fortunately, though these weapons have been conceived of and discussed, none have been built or tested (as far as we know).
These are fusion weapons that would not need a fission trigger for the thermonuclear explosion. Active research is going on in the US to develop these weapons, but with no success so far. Since there is no fission trigger, pure fusion weapons could be made with very low yields. Yet, the lethality of these weapons due to nuclear radiation and explosive force would still be great. For instance, a pure fusion weapon with an explosive force equivalent to one ton of TNT would kill people in an area nearly a hundred times larger than a conventional bomb with the same explosive force.
Another feature of these weapons is that since they do not use fissile material, their development would not be restricted by the FMCT (FMCT is discussed later).
Nuclear reactors harness the energy produced in nuclear reactions to generate electrical power. They are also used to power the motors of ships and submarines. In order to do this, reactors are designed to precisely control the rate of the nuclear reactions taking place in them. The energy is then released at a controlled rate and can be used to run turbines which generate electricity or run motors. The reactors at Kalpakkam, for instance, produce electricity in this manner.
Although nuclear reactions take place in a reactor just as they do in weapons, the crucial difference is that the rate of the nuclear reaction is controlled in a reactor whereas in a weapon, once triggered, the reaction proceeds in an uncontrolled way leading to the explosion.
As an analogy, in a car engine petrol is burned in a controlled way inside the cylinder to drive the motor. On the other hand if a lighted matchstick is dropped into the fuel tank the same petrol will burn in a completely uncontrolled way and could lead to an explosion.
As can be visualized from the analogy, a nuclear reactor is a complex mechanism compared to a bomb.
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