Fusion reactions

All of today’s reactors are based on nuclear fission. At the same time, the energy of the Sun and the devastating power of a hydrogen bomb are both the result of fusion reactions.
 
Fusion is a nuclear reaction during which two atoms of smaller masses join together into a heavier nucleus. This process can be both endothermic and exothermic depending on the initial nuclei’s atomic masses. Iron and nickel are the most stabile of all elements (they have the highest binding energy).  If the elements that take part in the fusion are lighter than iron, the process is accompanied by energy release, otherwise energy needs to be invested. This reaction takes place in the stars and the hydrogen bomb. The fusion of elements heavier than iron (because of them being endothermic) require extreme conditions, like in the case of a supernova explosion.

All the elements existing in nature were produced during supernova explosions.
The simplest fusion reaction which could be used as energy source is the joining of deuterium and tritium - two isotopes of hydrogen - into helium. Tritium can be easily produced, while deuterium can be found in the seas in great quantities. The problem is that these reactions need 100-300 °C to start and because no material can support this heat, the fuel has to stay far off the reactor’s wall.
In the 1990s, the Joint European Torus, during a research with an experimental fusion instrument showed that this technology could be used very well in practice.

Nuclear weapons
A nuclear weapon’s energy originates from some kind of nuclear transformation. These weapons are extremely destructive: one of the kind can destroy a whole city. They were used twice in history apart from experimental explosions: in the Second World War, when the United States of America threw them onto two Japanese cities, Hiroshima and Nagasaki.
Nuclear weapons are also called fusion or fission weapons, depending on the source of their power. The differences often vanish between the two types because almost in all modern nuclear weapons they are used together: with the help of a smaller fission bomb are the conditions, the temperature and pressure, assured to start the fusion; on the other hand, fission bombs are more effective if a fusion nucleus sets afloat the energy of the respective bomb.  Because both fission and fusion bombs release their energy by altering the nucleus, the most precise denomination for them is ‘nuclear weapon’.
Fission bombs
Fission bombs obtain their energy from nuclear fission: heavy nuclei (uranium or plutonium) fissure into lighter elements through neutron injection (these produce new neutrons, which bombard further nuclei, resulting in a chain reaction). Due to historical reasons, they are called atomic bombs. The naming is not precise because the chemical reactions release energy by the joining of nuclei, while the fusion (the joining of nuclei) is no less of atomic nature than the fission (the separation of nuclei). Thus this misunderstanding, the expression atomic bomb is widely spread and used especially for fission bombs but also for any kind of nuclear weapons.

Fusion bombs
The basis of fusion bombs is the joining of nuclei, when lighter nuclei join into heavier ones, like helium or hydrogen. The process is accompanied by a great release of energy. The most common name for them is hydrogen bomb because of their basic material; or thermonuclear weapon, because the temperature has to be very high to start the chain reaction.

What purposes does each nuclear weapon serve?
Tactical nuclear weapons are not that powerful (from the smallest, 0.3 kilotons, to the largest, a few hundred kilotons) and are used on battlefields.
They can be:

• Artillery weapons
• Anti-submarine bombs

• Classic (gravitational) bombs
• Ground-air missiles (against aircrafts and intercontinental missiles)
• Anti-satellite bombs

Strategic nuclear weapons are very powerful (from a few kilotons to the theoretically 100 megatons of a hydrogen bomb). Their targets are inimical towns (which they can destroy completely), launch pads or general staff air-raid shelters. They are often fixed on intercontinental rockets to raise their range with thousands of kilometres. A submarine equipped with such a weapon can destroy a target on any corner of the world.
 What are the effects of a nuclear detonation?
The energy released during the fission can manifest itself in more ways:

• Blast (40-60%)

• Electromagnetic impulse (40-60%). Beginning from heat radiation and visible light, to X-rays, every frequency is to be found in its spectrum.
• Radioactive radiation (10-20%). Mostly neutron- and gamma radiation. The nuclear fallout has to be mentioned too.

The energy distribution shows that nuclear weapons do not differ in many things from classic bombs: only the blast and heat radiation have significant destructive effects. In many cases the radioactive radiation can be irrelevant. But there is significant difference considering the amount of released energy: an atomic bomb releases a lot more energy in much shorter time. Therefore the power of a nuclear weapon is measured in the power of the equivalent amount of TNT. An ordinary atomic bomb has the power of 10-1,000 kilotons TNT. The bomb dropped on Hiroshima had 15 kilotons while the biggest, the soviet Tsar bomb was appreciated to 50-100 megatons.

In the case of a detonation, the temperature can raise to more hundred millions Kelvin. If so, atoms transmit their energy mainly in the form of X-rays. In just a few meters, the air absorbs the radiation completely and therefore warms up. When the detonation happens in the air, a fireball is formed which starts to widen and raise. If a one megaton bomb explodes, after the