Physics GCSE 3 aqa

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Physics ­ Atomic structure, Ionising radiation, Half-life, radiation safety and nuclear radiation
Atomic structure
The Rutherford scattering experiment
John Dalton, in 1804, thought that matter was made up of time spheres, `atoms,' that couldn't be broken up
­ but he reckoned that each element was made up of a different type of atom
Nearly 100 years later J J Thompson discovered that electrons could be removed from the atom (disproving
Dalton's theory that atoms `couldn't be broken'). Thomas thought that atoms were spheres of positive
charge with tiny electrons stuck in them ­ the plum pudding theory
In 1909 Rutherford and Marsden tried to prove the plum pudding theory.
1. A beam of alpha particles was aimed a very thin gold foil ­ and their passage through the foiled was
detected. They expected that the alpha particles would pass straight though the foil, and maybe
produce a hole in the foil
2. However something else happened ­ some of the particles emerged from the foil at different
angles and some even bounced of the foil and came back
3. This must mean that the positive alpha particles were being repelled by tiny positively charged in the
atom
4. As a result of this experiment the plum pudding model was rejected and replaced by the nuclear
model of the atom.
5. The reason for this is the vast majority of the alpha particles go strait. Some of the alpha particles are
deviated through small angles because the nucleus and the alpha particles have the same charge
(positive).
6. 1 in 8000 alpha particles rebounded meaning the nucleus must be small and they must be positively
charged because it repelled the alpha particle sit also must be concentrated into a small area, he
knew that the electrons had very little mass thus creating the nuclear model of the atom. It also
shows that most of the atom (gold particles) is just an empty space.
Radioactivity and background radiation
Isotopes are different forms of the same element.
Same protons but different amount of neutrons-same atomic number but different mass number.(carbon ­ 12
and carbon ­ 14 are good examples of isotopes )
Most elements have different isotopes but there are usually only 1 or 2 stable ones
The other isotopes tend to be radioactive so decay to form other elements and give out radiation.
Radioactivity is a totally random process
Radioactive substances give out radiation from the nuclei of there atoms this process is entirely random you
don't know which nuclei is going to decay and you can't do anything to make them decay, it is completely
unaffected by physical conditions e.g. Temperature
Radioactive substance spit out one or more of the three types of radiation, alpha, beta and gamma
Background radiation
Background radiation is always present around us ­ it comes from:
Unstable isotopes which are all around us (in the air, food, in
building materials and rocks)
Radiation from space ­ known as cosmic rays come mostly from
the sun

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Radiation from man ­made sources e.g.…read more

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The Nuclear and Uranium miners get 10 times as much radiation as the average person ­ they have
special suits
o Radiographers (X- ray people) ­ they wear lead aprons and stand behind lead screens to protect
themselves
o Cabin crew and flight crew ­ they have more exposure to the sun's rays
o Miners get exposed because of the rocks
Half Life
Radioactivity of a particle always decreases over time
As the unstable nuclei continue to disappear the less radioactive it becomes
The problem…read more

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Unfortunately they do kill some normal cells which can be quite damaging to the patient (that's why
it is considered slightly risky)
Sterilization of food and surgical instruments
o Uses gamma rays
o High dose of gamma rays which will kill any microbes in them
o It is called irradiation
o Good because it sterilizes plastic instruments without high temperatures (which could cause them
damage)
Radioactivity Safety
Marie Curie discovered radium in 1898
o No one knew of its dangerous and so it was used…read more

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