Physics 2 (P2) Radiation

Note I did not make this resource, I think others should be able to access it to aid revision

P2 radiation notes, EDEXCEL specification; Could still be relevant to other exam boards; Foundation and Higher Tier

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Ionising radiation (P2- topic 11) Putting radiation to use
The more ionising a radiation is, the less penetrating it is. Particles that are strongly ionising collide with atoms and
knock off electrons. It means they give up their kinetic energy faster, and so cannot penetrate far into materials.
Ionisation is where atoms gain or lose electrons, turning them into charged particles called ions.
Alpha (Helium Nuclei) Beta (Electrons) Gamma rays (Short wavelength
EM waves)
Big, heavy & slow moving (10% Small and fast moving (half the Travels at the speed of light
of the speed of light) speed of light)
+ 2 charge -1 charge 0 charge
Strongly ionising Moderately ionising Weakly ionising
Do not penetrate far (0-10cm) Penetrate moderately before Pass through rather than collide
Used in smoke detectors. colliding (10cm-3m) For every penetrate far into materials.
particle emitted a neutron turns
to a proton in the nucleus
Alpha particles are blocked by paper
Beta particles are blocked by thin aluminium (skin will not block beta)
Gamma rays are blocked by thick lead
X rays and gamma rays come from different sources. Gamma rays are produced naturally from the nuclei of atoms
when they decay. But on earth, x rays are artificially produced in special x ray machines. X rays and gamma rays have
similar frequencies, so you can only tell them apart if you know where they came from.
Ionisation from alpha sources can be detected using a cloud chamber. The air inside is saturated with alcohol and is
cooled by dry ice underneath. Alpha particles ionise air molecules as they pass through. These ions will cause droplets
of alcohol to form and leave a trail. Beta trails are harder to see because they are less ionising, and gamma rays are
too weak to form trails.
Gamma radiation can be used to detect leaks underground in pipes. To do this, you need a small amount of a material
that release gamma radiation for a small amount of time. The gamma source is placed on the pipe. Where there is
fluid leaking, gamma radiation becomes concentrated, the gamma rays penetrate through the ground to the surface.
The leak can be pinpointed and repaired.
Background radiation
Background radiation comes from many sources
1. Naturally occurring in unstable isotopes. In the air, food, building materials and rocks.
2. Radiation from space. Known as cosmic rays. They come mostly from the sun, but we are protected by the
earth's atmosphere. Also the earth's magnetic field deflects cosmic rays away from earth.
3. Human activity e.g. fallout from nuclear explosions or dumped nuclear waste, but this is only a tiny amount
of background radiation.
The levels of background radiation can change depending on where you are
It increases at higher altitudes because of more exposure to cosmic rays
Underground in mines ­ because of the rocks underground
Underground rocks like granite can cause higher levels of radiation at the surface, if they release radioactive
radon gas this can get trapped inside people's houses.

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Radioactivity is completely random and is not affected by chemical bonding or temperature changes. Uranium- 238
decays firstly by alpha. And carbon-14 decays by beta.
Uses of radiation
Smoke detectors
1. A weak source of alpha radiation is placed in the detector, close to two electrodes (americium-241)
2. The alpha source causes ionisation and the current flows
3. When there is a fire, smoke will absorb the radiation. Current stops and the alarm sounds.
Tracers in medicine
1.…read more

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Radioactive safety
Outside the body, beta and gamma sources are the most dangerous because they can get inside your body and your
organs but alpha cannot penetrate the skin
Inside the body, alpha sources are the most dangerous because they cannot get out and do damage in a localised
In a school lab
1. Always use tongs
2. Hold the source t arms length
3. Keep the source away from you and don't look directly at it
4.…read more

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1. A slow moving neutron is fired at the uranium-235 atom. This neutron is absorbed by the nucleus, this makes
the atom unstable and causes it to split
2. When the uranium-235 splits it forms two new lighter elements (daughter nuclei). There are lots of different
pairs which uranium can be split into. E.g. krypton-91 and barium-143, but they are all radioactive because
they have the `wrong' number of neutrons in them
3.…read more

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The fission reactions make the fuel rod hot. However a single fuel rod loses neutrons from its edges, so the
fuel rods are put close together in the reactor core. Meaning more neutrons are absorbed; and increasing
the amount of fission reactions. The temperature of the rods is over 500 degrees.
3. If the fuel rods become too hot, engineers slow down the chain reaction by lowering control rods between
the fuel rods. When demand is high, the control rods are raised. And vice versa.…read more

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Scientists have actually had some success with fusion reactors called tokomaks. It takes more power to run than it
produces so it is not yet a viable source of energy, but scientists are working on improvements to fusion.
A tokomak has a doughnut shaped ring of magnets to hold the intensely hot hydrogen under pressure without
touching the sides.
Electric shocks
Some materials, like nylon, will pick up extra electrons when they are rubbed.…read more

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Aircraft fuelling
1. As fuel flows out of the fuel pipe, the fuel gains electrons from the pipe giving it a (-) charge and the pipe a
(+) charge.
2. The voltage between the pipe and the fuel can easily cause a spark. Which would ignite the fuel and cause an
3. To solve this, the plane fuel tank needs to be connected to earth with a metal strap so that the charge is
conducted away, rather than building up.…read more


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