Study material
The effects of nuclear weapons
The effects of a nuclear explosion are what makes nuclear weapons such a devastating weapon, setting them apart from any conventional weapon (which means regular weapons, not of mass destruction).
A conventional bomb causes its greatest damage through blast and heat and their indirect effects. A nuclear explosion causes the same kind of death and destruction, but a thousandfold more of it. In addition to that, nuclear weapons kill through radiation. A nuclear war would also have great indirect effects, not only for the countries at war but for the population of other parts of the world as well.
Direct effects of nuclear weapons
When a nuclear weapon detonates, the gigantic forces inside the atomic nuclei are set free. During the explosion, an intense, blinding light as from a tremendous lightning-bolt is seen. Within a certain radius, everything is burnt to ashes. There is no chance of escaping this thermal radiation unless you have advance warning.
Everything at the site of explosion is pulverized and burnt away. All that is left is smoke, gas and small particles rising into the air. These form a mushroom-like cloud.
Just as quickly, you are hit by ionising initial radiation which causes radiation illness, together with an electromagnetic pulse that destroys electrical equipment. Neither of these forms of radiation can be seen. Next, the blast reaches you. It is violent enough to smash houses and crush humans at a distance of several kilometers.
These immediate effects are followed by a radioactive fall-out, making large areas lethally dangerous to be in for a long time to come.
Initial radiation
Initial radiation is the first radiation to appear after a nuclear weapon has detonated. It consists of gamma and neutron radiation emitted at the moment of explosion, lasting for at most a minute. This radiation causes damage to humans, animals, the environment, electronics etc.
The neutron bomb is a form of hydrogen bomb which delivers a very high amount of initial radiation. You might say that this bomb kills humans, but leaves houses and other buildings. Most of the energy comes in the form of radiation and only a slight part is turned into shock and heat.
Elektromagnetic pulse (EMP)
EMP is caused by gamma radiation hurtling through the air, knocking electrons out of the atoms of air molecules. These electrons combine to form a strong pulse of electric current, generating an electromagnetic field. This field then expands as a very short-lived wave, the electromagnetic pulse. EMP causes disturbances and damage in electronic equipment.
EMP is a serious threat to our modern society, since a major part of the infrastructure is constructed around electronics. There are numerous items that can catch and pass on electromagnetic energy, such as aerials and other antennae, telephone wires, railway tracks and so on. This energy can end up in computers and other sensitive equipment and cause damage to vital systems, like those supplying water or electricity, or telecommunications. Without these systems, our society is extremely vulnerable.
Thermal radiation
The nuclear explosion produces an enormous fireball, which generates an intense heat, grows at a tremendous speed and then rises with the hot air. As it gains altitude, the fireball cools down, forming the mushroom-shaped cloud that characterises a nuclear explosion.
Mushroom shaped cloud after a nuclear detonation
This heat, the thermal radiation, causes severe burns on humans. Other material can be ignited and start raging fires.
Blast
The blast is caused by the great pressure within the fireball. The amount of energy released at a nuclear explosion is enough to raise the temperature to tens of millions of degrees centigrade. The very matter of the bomb is transformed into a ball of fiery gasses. The great pressure boost of this scalding gas causes the fireball to expand in a blast that spreads faster than the speed of sound.
First you feel the shock like a giant slap in the face (the static overpressure), next in the form of a gust of wind reaching hurricane strength (the dynamic overpressure). Since air rushes out from the point of explosion at the same time as the fireball rises into the air, a vacuum is formed at the centre of the explosion. Because of this, the gale turns after some ten seconds, blowing back towards the centre again. The blast affects buildings and other structures, crushing them or tossing them about, as well as causing deaths and severe damage to people.
Radioactive fall-out
The radioactive matter that’s left of the nuclear weapon eventually falls to the ground, condensed on or into particles. This is called radioactive fall-out and comes on three different scales: local, intermediate or global fall-out.
In local fall-out, the radioactive particles are spread downwind and fall to the earth within a day. In some of the affected areas, the radioactive doses can be directly lethal to exposed humans.
The particles destined to become intermediate fall-out go directly into the troposphere (the layer of air closest to the earth) after the explosion. They quickly orbit the Earth a few times and then fall down during the span of some weeks. This fall-out can lead to damage in humans and, in the long run, to an increase in the numbers of cancer cases and genetic damage. The short-term are discussed in the section Radiation damage".
The global fall-out is not thought of as any direct threat to humans. But when humans eat food or breathe air contaminated by radioactive particles, this may cause damage. After the explosion, the particles are taken up into the stratosphere (the upper atmospheric layer) and spread across the entire globe. It will slowly fall down after months or years have passed. Since the radioactivity will have largely decayed after all that time, this fall-out is not considered very harmful to us humans.
Updated September 25, 2005
Quick review (Click to read the answers)
- What is the term for the radiation that first occurs from a nuclear detonation?
- What damage is caused by the electromagnetic pulse?
- A nuclear detonation gives rise to a fireball that grows at an enormous speed, and then rises.What happens when the fireball rises and gets cooled off?