Radioactivity

Radioactivity

• Radioactivity usually occurs when the nucleus of an atom becomes unstable, causing them to decay. Atoms can decay into 3 different types of particles - an alpha particle, a beta particle, or a gamma particle (ray).
• The amount of radiation given off can be detected through the use of a Geiger counter. The number of Nuclei that decay, which in turn gives off radiation, in a second is the activity of the material. This number is measured in Becquerals (Bq).

Alpha Decay

• Alpha Decay removes 4 off the atomic mass number and 2 off the atomic number atom by decaying the atomic mass number by 4, and the atomic number by 2. This creates a new substance whilst emitting an alpha particle, which has atomic mass number 4 and atomic number 2.
• The alpha particles are the most ionising particle. This means that it will decay an atom the most of any particle, which makes it very dangerous to the human body. However, this atom can only travel a short distance, and can be stopped by substances as thick as paper. This means that it can mostly only harm the body if swallowed.
• Alpha particles can be used in smoke detectors, as if the smoke blocks the emitter from the reciever, it will sound off the alarm.
• Ionising - Radiation that has enough energy to cause other atoms to lose electrons and form ions (Definition from BBC Bitesize)

Beta Decay

• Beta Decay changes a neutron into a proton and an electron. This electron is then shot out the atom, which is then known as a beta particle. This means that the atomic mass number remains the same, bu the atomic number increases by 1 due to gaining another proton.
• Beta Particles have moderate ionisation. They can still be dangerous, but they are not as harmful as alpha particles.They are able to pass through paper, but are stopped by things as thick as alluminium.
• This means that Beta Particles are used to make sure that paper stays at its proper thickness. This is because if the paper becomes too thick. beta particles will stop passing through it, which will make the reciever adjust the paper to be thin enough.

Gamma Decay

• Gamma Decay emits an energy wave that can pass through paper and alluminium, but it can be stopped by things thick lead. Gamma Decay does not affect the atom at all, so the atomic mass number and mass number remain the same.
• Gamma rays are the least ionising particles. They are mostly unable to harm the human body, and usually just pass straight through us without any damage to our bodies.
• Gamme Rays are able to be used to clean medial equipment. This is because they are unable to damage the medical equipment, but they also destroy any and all bacteria that is on the equipment, so that it can be used for the next person.

Nuclear Fission

• Nuclear power reactors use a reaction known as nuclear fission as an energy source. Two isotopes in common use as nuclear fuels are uranium-235 and plutonium-239. These atom have large nuclei that can easily be split when hit by a neutron.
• When either of these nucleus' are hit by a neutron:
• The nucleus splits into two smaller nuclei, which are known as daughter cells. These are radioactive.
• Two or three more neutrons gets released
• Some energy is released
• These extra neutrons may also hit other uranium or plutonium nuclei, causing them to split as well. This can start a chain reaction where more and more nuclei split due to neutrons constantly being released. Chain reactions are controlled so that it does not use up all the energy too quickly.
• All nuclear reactors produce radioactive waste. The most dangerous of this waste gets sealed in glass-like blocks, buried in deep rock. Careless disposal of radioactive waste has led to pollution.

Nuclear Reactors

• As well as producing heat, the nuclear reactor can make other matierials radioactive. If a matierial is put into a reactor, some of the neutrons released by the chain reactions will be absored by the matiels nuclei. This makes an atom's nucleus unstable, making it radioactive. These matierials are often used as tracers in hospitals for diagnosis and treatment, or industry to detect leaks in pipes.
• The Nuclear Reactors are also designed to allow controlled chain reactions to happen. Each time a uranium nucleus splits, it releases energy and three neutrons. If all of these neutrons are allowed to be absored by other uranium nuclei, the chain reaction will spiral out of control, which will create an explosion. To control the energy. moveable control rods are placed between the fuel rods. These rods are made of boron, which elps to absorb some of the neutrons which meanfs fewer neutrons are avalaible to split uranium nuclei. These rods are raised to increase and lowered to decerase the number of free neutrons.

Nuclear Fusion

• Nuclear Fusion involves a deuterium and a tritium nucleus colliding and being forced together. Both nuclei have a positive charge, so this make them repel. This is known as electrostatic repulsion. The nuclei must get very close in order to collide. This is roughly a million millionth of a millimetre. If the nuclei are moving fast they can overcome the electrostatic repulsion. The nuclei will move faster if its molecule is hotter, which will increase the chance of collision.
• For a nuclear fusion reactor to work, the temperature and pressure must be very high, which is difficult to reproduce and costs a lot to do. This makes nuclear fusion a bad energy source to use.

Credits

• Many facts recorded from BBC bItesize
• http://www.bbc.co.uk/schools/gcsebitesize/science/add_edexcel/fission_fusion/fissionfusionrev1.shtml