Physics: Structured Paper P2 - Topics 11 & 12

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Ionising Radiation

Alpha particles are Helium Nuclei.
- Big, Heavy and Slow Moving. 
- Strong positive charge.
- Big Mass & Charge - Strongly Ionising.

Beta Particles are Electrons.
- Between Alpha and Gamma. - Quite fast & Quite small.
- Negative charge.
- Moderatley ionising.
- For every one emitted, a neutron turns into a proton in the nucleus. 

Gamma Rays are a very short wavelength EM waves.
- Opposite of Alpha particles.
- Pass through, instead of collide.
- Weakly ionising. 

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Background Radiation

Comes from many sources.

- Unstable isotopes - air, food, rocks. 
- Radiation from space - cosmic rays, from the sun.
- Human activity - Nuclear explosions

Changes depending on where you are.

- Increases at high altitudes because of exposure to cosmic rays.
- Increases under the ground, because of all the rocks.
- Places with RADON GAS.


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Atomic Structure

The nucleus contains protons and neutrons.

Most of the mass of the atom is contained in the nucleus, but is tiny.

The Electrons fly around the outside of the nucleus.

RM: Relative Mass
RC: Relative Charge 

Proton: RM: 1 / RC: +1
Neutron: RM: 1 / RC: 0 
Electron: RM: 1/2000 / RC: -1 

Isotopes are atoms with the same number of protons but a different number of neutrons.

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Uses of Ionising Radiation

Smoke Detectors: A weak source of alpha radiation is placed in the detector, close to two electrodes.
If there is a fire then smoke will absorb the radiation.

Tracers im medicine: GAMMA

Radiotherapy: GAMMA

Sterilisation of food: GAMMA

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Radioactive Safety

Radiation harms living cells.

Alpha, Beta and Gamma radiation enter living cells and collide with molecules.

These collisions cause ionisation - these damage/destroy molecules.

This can cause mutant cells to divide uncontrollably.

The Extent of harm depends on:
- How much exposure
- The energy and penetration of the radiation

Outside the body Beta and Gamma are most dangerous.
Whereas Alpha is more dangerous inside. 

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Splitting The Atom

Scientists use theories to make predictions.
One of these led to NUCLEAR FISSION. (The splitting of Uranium atoms)

1) A slow moving neutron is fired at uranium.
The neutron is absorbed by the nucleus.
2) When it splits is forms 2 new lighter elements. (Daughter nuclei)
3) Each uranium atom splits up, it spits out two or three neutrons. (Chain reaction)
4) Each nucleus splitting gives out a lot of energy.

Nuclear fission products are RADIOACTIVE. 

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Nuclear Power

Nuclear Power Stations are really glorified steam engines.

They are powered by nuclear reactors.
In the ractor, a controlled chain reaction takes place (Uranium splits up)

The fission releases lots of energy. (Thermal)
This heat is used to boil water to drive the steam turbine.


Free neutrons 'kick-start' the reaction.
The daughter products collide - causing temperature to rise.
Control rods limit the excess neutrons.
Carbon dixoide is pumped through to carry heat away.
The gas is put in a heat exchanger, where it is changed into water.
Water is the useful product.

Nuclear power is very clean, but there are few ways to dispose of the waste.
There is also risk of leaks. 

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Nuclear Fusion

Nuclear Fusion is the joining of small atomic nuclei.

This process is basically the opposite of Fusion.

Two light nuclei combine to create one big nuclei.

Fusion happens only at very, very high temperatures. - No material can withstand these kind of temperatures (10 000 000 C)

You have to contain products in a magnetic field.
There are few experimental reactors for this, the only one at the moment is JET
(Joint European Torus) 

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Static Electricity

The build up of static electricity is caused by Friction.

When two insulating materials are rubbed together, electrons will be scraped off one and dumped onto another.
One will have a positive charge and the other a negative charge.
Electrically charged objects attract small objects placed near them.

Only electrons move, only the positive charges.
A positive static charge is always caused by electrons moving away elsewhere.

Earthing - A charged conductor can be discharged safely by connecting it to earth with a metal strap.

Like charges repel, opposite charges attract.
As charge builds up, so does voltage. 

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Examples of Static Electricity

- Fingerprinting (dust sprinkled, positive charges attracted to this)

- Laser printing (laser beam scans accross positive charges)

- Clothing Crackles (electrons get scraped off, leaving positive charges)

- Car Shocks (charge built up between clothes and car seat)

- Lightning (raindrops and ice bump together, knocking off electrons)

- Aircraft Fuelling (voltage between fuel and pipe)

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