Nuclear Energy

Structure of an AtomWe have studied the structure of an atom previously and we know about the three main subatomic particles: protons, neutrons and electrons.

What makes the protons and electrons stay together in an atom?A force called the strong force opposes and overcomes the force of repulsion between the protons and holds the nucleus together. The energy associated with the strong force is called the binding energy. The electrons are kept in orbit around the nucleus because there is an electromagnetic field of attraction between the positive charge of the protons and the negative charge of the electrons.

Radioactivity

In most cases, elements like to have an equal number of protons and neutrons because this makes them the most stable. Stable atoms have a binding energy that is strong enough to hold the protons and neutrons together.

However, an additional neutron or two may upset the binding energy and cause the atom to become unstable. In an unstable atom, the nucleus changes by giving off a neutron to get back to a balanced state. As the unstable nucleus changes, it gives off radiation and is said to be radioactive.

All elements with atomic numbers greater than 83 are radioisotopes meaning that these elements have unstable nuclei and are radioactive. Elements with atomic numbers of 83 and less, have isotopes (stable nucleus) and most have at least one radioisotope (unstable nucleus).Examples of chemical elements with radioactive atoms include uranium, plutonium & radium. As atoms give out particles or rays they change into atoms of simpler elements. For example, uranium changes to thorium. This change is called radioactive decay. When there is a change in the nucleus and an element changes into another element, it is called transmutation. It happens at different speeds or rates for different radioactive elements.

changes to

Radioactivity can be dangerous since it harms living things. But under controlled conditions it is very useful in medicine and scientific research.

Nuclear FissionWhen alpha or beta particles (radiation) are emitted by a radioisotope, they collide with surrounding atoms and make them move faster. In other words, the temperature rises as nuclear energy is transformed into thermal energy (heat).

The diagram shows what can happen if a neutron strikes and penetrates a nucleus of uranium-235. The nucleus becomes highly unstable and splits into two lighter nuclei. This splitting process is called nuclear fission. If emitted neutrons go on to split other nuclei, the result is a chain reaction. Whenever particles penetrate and change a nucleus, this is called nuclear reaction.

During the process of fission, bits of matter cease to exist and become vast quantities of energy instead. The energy produced is given by ΔE = Δmc 2 where Δm is the lost mass in kg and c is the speed of light in m/s.

Albert Einstein postulated this theory that mass could be converted into energy.

Mass-Energy Equivalence

Nuclear ReactorsA nuclear reactor is a device or a furnace where controlled fission chain reaction is carried out and the energy released is used to generate electricity. The reactor uses Uranium rods as fuel, and the heat is generated by nuclear fission: neutrons smash into the nucleus of the uranium atoms, which split roughly in half and release energy in the form of

Carbon dioxide gas or water is pumped through the reactor to take the heat away, this then heats water to make steam. The steam drives turbines which drive generators. Modern nuclear power stations use the same type of turbines and generators as conventional power stations.

heat. In nuclear reactions, the energy released per atom is around a million times greater than that from a chemical change such as burning.

Nuclear FusionThe Sun and other stars are mostly made of Hydrogen. At the centre of the Sun, tremendous temperatures and pressures make the hydrogen nuclei collide at such high speeds that they join together (fuse) to form helium nuclei. As this happens, huge amounts of energy are released as heat and light. The energy travels up to the Sun’s glowing surface and then passes through space to reach Earth.

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