edexcel P2 topic 5

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Topic 5 ­ nuclear fission and nuclear fusion
Radioactivity
Atoms are made up of sub-atomic particles which are protons,
neutrons and electrons. Electrons can be lost or gained and this
forms charged particles called ions.
Some materials are radioactive because the nucleus of each atom is
unstable and so can decay or split up by giving out nuclear radiation
in the form of alpha particles, beta particles or gamma rays. This is a
random process and the nucleus will often change into a new
element.
The radiation can be detected by using a Geiger counter. The
activity of the material is the number of nuclei that decay and give
off radiation every second. This is measured in Becquerel (Bq). The
activity of the radioactive material will decrease with time and this
can be shown by the falling count rate, measured using a Geiger
counter.
An unstable nucleus gives out:
Alpha particles
Beta particles
Gamma rays
Ionisation is when an atom loses or gains electrons and turns into
an ion. Alpha, beta and gamma are all ionising radiation which
means they can cause the ionisation of other atoms.
The nucleus of an atom can be represented as:
Where A = atomic mass (protons + neutrons), Z = atomic number
(protons) and X = chemical symbol.

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Alpha particles
An alpha particle has 2 protons and 2 neutrons. When an alpha
particle is emitted from a nucleus, the nucleus loses 2 protons and 2
neutrons therefore the atomic mass decreases by 4 and the atomic
number decreases by 2. A new element is formed.
Alpha particles have a big mass and are slow-moving therefore
increases the chance of ionisation.…read more

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A gamma ray is a high energy electromagnetic radiation. It can
transfer energy to electrons orbiting an atom and if it gets enough
energy, it can break free from the atom. Gamma rays are the least
ionising however the most penetrating (can be stopped by thick
lead)
Nuclear fission
Nuclear fission is a reaction used in nuclear power reactors and it is
a source of energy for generating power. The two common isotopes
used as nuclear fuel are uranium-235 and plutonium-239.…read more

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Electricity goes to the transformers via national grid to
produce the correct voltage.
The difference between fossil fuel and nuclear power stations is the
way the water is heated. Fossil fuel power stations burn their fuel
while nuclear power stations use fission to generate heat.
All nuclear reactors produce radioactive waste. The most dangerous
waste is sealed in glass-like blocks buried within rocks. Careless
disposal of waste leads to pollution of land, rivers and the ocean.
The nuclear reactor can make other materials radioactive.…read more

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Nuclear fusion is when to small atomic nuclei join (fuse) to create a
large nucleus (e.g. 2 hydrogen = helium). Energy is released
therefore it can be used as a source of energy.
The sun and other stars use nuclear fusion to release energy and it's
when hydrogen nuclei join to form helium nuclei.
Fusion doesn't leave behind a lot of waste and hydrogen is
renewable unlike uranium (non-renewable)
Fusion only happens when the temperature and pressure is high.…read more

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