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"Plum Pudding" theory
· J Thomson discovered that electrons could be removed from atoms.
· He suggested that atoms were "tiny spheres" of a positive charge, and
negatively charged electrons dotted around inside it.
· Like plums scattered in a plum pudding.…read more

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Rutherford's Scattering
experiment
· Rutherford fired positively charged alpha particles at gold foil.
· Most passed through the foil and some were deflected.
· But the plum pudding theory suggests that all alpha particles should have
been deflected as like charges repel.…read more

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Background Radiation
· Most background radiation is from natural sources.
· Cosmic rays- radiation from space that reach the Earth.
· Radon gas- rocks and soil that are radioactive give off radon gas.
· Food- plants absorb radioactive materials which gets into food chains.
· Others are man made.
· Power- nuclear waste from creating energy.
· Medical- x-rays and radiotherapy.…read more

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Structure of an Atom
Rutherford concluded that that most of the mass is concentrated in the centre of the atom
and that the centre has a positive charge. The centre/ nucleus is surrounded by negatively
charged electrons with spaces between them.
Particle Charge Mass
+ Nucleus=
+ proton 1+ 1
protons and
neutrons neutron 0 1
electron 1- 1/1800
electron
space…read more

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Alpha Radiation
· Is the most ionising type of radiation. (Up to 2000 ionisations per
decay).
· easily blocked by matter.
· Is the same as a helium nucleus: 2 protons and 2 neutrons.
· Elements emit alpha particles to become more stable.
· Biggest and heaviest
Alpha decay:
6 electrons
Gamma
4 neutrons
4 protons radiation
Alpha particle…read more

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