All revsion notes for p6

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P6 ­ Radioactive Materials
Atoms consist of a nucleus and orbiting electrons. The nucleus of an atom
contains protons and neutrons. It makes up most of the mass of the atom,
but takes up virtually no space.
The electrons that orbit the atom are really small. They whizz around the
outside of the atom. Their paths take up a lot of space, giving the atom its
overall size (though it's mostly empty space).
Every atom of a particular element has the same number of protons in its nucleus. However the
number of neutrons isn't fixed. Many elements have a few different isotopes ­ atoms with the same
number of protons but different numbers of neutrons.
Radioactive Atoms
Some elements emit ionising radiation all the time ­ these elements are radioactive. Radioactive
atoms are unstable as they break up (decay) to make themselves more stable. Unstable atoms can
decay at random meaning you can't predict when it will happen ­ it is completely unaffected by
physical conditions (temperature) or chemical processes (bonding).
When an atom does decay, it spits out one or more of three types of ionising radiation ­ alpha, beta
and gamma. During the decay process, the atom often changes into a new element.
Ionising radiation can transfer enough energy to break an atom or molecule into bits called ions ­ this
is called ionisation. These ions can then go on to take part in other chemical reactions.
There are 3 types of ionising radiation (alpha, beta and gamma) which are all emitted by radioactive
Alpha Radiation
Alpha particles are relatively big and heavy and fairly slow moving, meaning that they don't
penetrate far into materials as they're stopped quickly. They are realised by a heavy nuclei (uranium).
An alpha particle is a helium nucleus (He) which is made up of 2 protons and 2
neutrons. Alpha particles have a mass of 4 and a charge of +2. Their decay
always changes the element of the atoms that's decaying, since it loses
A typical alpha emission:
Beta Radiation

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Beta particles move quite fast and they are quite small. They penetrate moderately into materials
before they are stopped. Beta particles are released by nuclei that have too many neutrons.
During beta decay, a neutron in the nucleus turns into a proton, so the element
changes, and a beta particle is emitted.
A beta particle is identical to an electron, with virtually no mass and a charge of -1.…read more

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Ernest Rutherford
In 1909, Ernest Rutherford, Hans Geiger and Ernest Marsden tried firing positively charged alpha
particles at thin foil. Most of these particles just went straight through but the odd one came straight
back at them.
This meant:
Most of the mass of a gold atom was concentrated at the centre in a tiny nucleus. The rest of the
atom must be mainly empty space ­ as most of the alpha particles went straight through the foil.…read more

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Nuclear reactions release a lot more energy than chemical reactions. Splitting a gram of uranium
releases over 10,000times more energy than burning a gram of oil. You can calculate just how much
energy is released by using E = mc2.
Nuclear Power Stations
In nuclear reactors, a chain reaction is set up. A neutron splits a nucleus, realising more neutrons.
These can then go on to split more nuclei and release more neutrons and so on.…read more

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Danger from Radiation
Alpha, beta and gamma radiation are all ionising radiation ­ they can break up molecules into smaller
bits of ions. Ions can be very chemically reactive, so they go off and react with thing and generally
make nuisances of themselves.
In humans, ionisation can cause serious damage to the cells in the body. A high doses of radiation
tends to kill cells outright, causing radiation sickness. Lower doses tend to damage cells without
killing them, which can cause cancer.…read more

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Radioactive sources are considered to be safe when the radiation they are emitting is at about the
same level as the background radiation. The half-life of the source gives an idea of how long it will
take for this to happen.
Ionising Radiation
Ionising radiation can be useful for...
Treating Cancer
Since high doses of gamma rays will kill all living cells, they can be used to treat cancers.…read more


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