N-weapons for dummies

The fission or atom bomb is the cruder assembly and uses either Plutonium-239 or the less productive Uranium-235. These are highly unstable elements whose nuclei undergo spontaneous decay, releasing neutrons which then destabilise neighbouring atoms, which release more neutrons, which move the reaction on to other atoms. In the normal state, this reaction cannot sustain itself because too many neutrons escape. It becomes a chain reaction only at critical mass when neutrons strike fresh nuclei at a high enough rate.

The classic fission bomb works on the principle of dividing a critical mass of nuclear fuel, keeping the components separate during flight, then propelling them together cataclysmically at the moment of explosion by a high-explosive gun8217;.

The modern bomb uses a single core of fissile material lower than critical mass. To initiate the explosion, shaped charges of conventional highexplosive are set off around it. An inward-travelling blast wave causes the core to implode8217;. As it collapses in on itself its density increases by up to three times, and it reaches critical mass. Thereafter, the explosion proceeds. Such implosion devices require precision machining; hence the large number of tests conducted by the nuclear powers.

The fuse of a hydrogen bomb is lit by an atom bomb. In other words, enough energy to devastate a city the size of Ahmedabad or Bangalore is needed just to start the reaction. The fuel is either the hydrogen isotopes Tritium and Deuterium both as liquefied gases, and hence difficult to handle or the solid precursor Lithium-6 deuteride. The reaction can proceed only at the temperatures and pressures of the core of the sun 8212; which, incidentally, also burns by fusion. On earth, such conditions exist only in the fireball of an atom bomb, whose temperature may by as high as 100 million degrees Kelvin, seven times the solar temperature. Themost popular hydrogen bomb remains the Teller-Ulam configuration, the original device which was tested at Bikini.

The cloud is preceded by a rapidly-expanding fireball. The exploding core emits low-energy X-rays, which ionise the surrounding air, making it transparent to light. The fireball becomes, as the Bhagavad Gita puts it, brighter than a thousand suns.

Then the core begins to cool. X-radiation slows down, to be replaced by ultraviolet and visible light, then by infrared. The speed of the shock wavefront slows down to the speed of sound, and turns incandescent. Then the explosion vanishes, because its light cannot penetrate the air superheated by the shock wave. It is seen again when the temperature starts to fall. This double flash8217; is what surveillance satellites look for 8212; the final confirmation that Armageddon has begun.

The mushroom cloud is seen last of all, when the radiation has fallen sufficiently for the vaporised 8212; andradioactive 8212; dirt sucked up by the explosion to become visible.

At ground zero 8212; graphically termed the vaporisation point8217; 8212; only two out of every 100 people may survive the explosion. But it is a very temporary reprieve. They will die in a matter of hours, if not minutes, of shock and flash radiation burns. The blast will raise the local air pressure by about 25 pounds per square inch, about the pressure needed to inflate a truck tyre. Wind speeds cross 500 kmph, enough to flatten a city of highrises into a level plain.

A 20 megaton fission explosion causes devastation over a radius of 55 km. Even at the edge of the zone, energy equivalent to that of a powerful tornado is released, destroying buildings and hurling people into the air. Thermonuclear devices tend to be considerably more powerful.

High-yield weapons are launched in Intercontinental or Intermediate Range Ballistic Missiles ICBMs and IRBMs.They may be launched at sea from submarines, or from silos on land. Cruise missiles can be launched from 747 aircraft. Low-yield weapons may be launched in standard ordnance shell casings, or may be carried to the battlefield by hand.

Attempts at disarmament predate the nuclear age. In 1932 and 1934, there were abortive attempts at conventional arms limitation at the Disarmament Conference of the League of Nations. The UN8217;s Disarmament Commission began the first talks on banning nuclear weapons in 1955. In 1957, the Russians walked out in disgust at the lack of progress. The first success was achieved through conventional diplomatic mechanisms in 1963 with the Partial Test Ban Treaty, to which India was a signatory. In a nutshell, it banned surface testing.

India chose not to join the Non-Proliferation Treaty of 1968, because it discriminated in favour of the five nuclear weapons states8217; who had conducted tests before 1967. Signatories have promised not tomanufacture or receive weapons and to open their facilities to full-scope8217; inspection by the UN-affiliated International Atomic Energy Agency. It is the latter clause that got Iraq, a signatory, into trouble recently.

Finally, there is the Comprehensive Test Ban Treaty CTBT, banning all testing, which India may now sign.

The most publicised treaties, the Strategic Arms Limitation Treaties SALT and SALT II were bilaterally negotiated between the US and the USSR in 1969-79. The Reagan administration abandoned SALT and renewed its dialogue under the optimistically named START 8212; Strategic Arms Reduction Talks 8212; in 1982. But real progress began only in the unipolar world and culminated in the SSD Safe, Secure Dismantlement programme in the former USSR, funded by the US under the Nunn-Lugar legislation. At the same time, the CTR Cooperative Threat Reduction programme was also launched.

Delivery systems are regulated by the Missile Control Technology Regime MTCR and there are treaties banningtesting in the air, at sea and on the seabed. Treaties also establish Latin America, Antarctica, Africa and outer space as nuclear-free zones.

The noteworthy point is that all the successful treaties were inter-governmental initiatives, and in every case, the trigger was public anxiety.

Yes, exactly 30 years ago this month in Paris, in the student demonstrations that sparked off the biggest general strike in France. The provocation was the wide disparity between government spending on education and that on defence, specifically independent nuclear deterrence. It is noteworthy that France remained vigorously active in nuclear testing even after that, until it signed the CTBT. But equally noteworthy is a line found scrawled on the wall of the Sorbonne after the rising: 8220;It isn8217;t over yet.8221; Its prophecy of a worldwide consensus against nuclear weapons is slowly coming true.