P6 - The Atom and Nuclear Fusion

THE ATOM AND NUCLEAR FUSION

In 1909, Ernest Rutherford tried firing alpha particles (which are + charged) at thin gold foil.

Most of the alpha particles went straight through the foil, but the odd one came straight back at him.

Rutherford realised that 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 empty space as most of the alpha particles went straight through the foil"

"The nucleus had to have a + charge otherwise the positively charged alpha particles wouldn't be repelled by the nucleus and wouldn't scatter"

Electrostatic Force - The force between particles that are caused by their electric charges

Strong force - The short range attractive force between protons and neutrons

The nucleus contains + charged proton particles which repel (drive/force back/resist) eachother

The nucleus is held together by the "strong force"which is much stronger than the electrostatic force between the protons.

The strong force only has a short range - it can hold protons and neutrons together when they're seperated by tiny distances

At larger seperations, the strong force is so weak that it practically dissappears 

Nuclear Fusion - When 2 nuclei fuse together to create a large nucleus and by doing so, release energy

Example: Hydrogen nuclei fuse together to make helium nuclie.

Nuclei can only fuse togetehr if they overcome the repulsive electrostatic force and get close enough for the strong force to hold them together. You need a lot of energy for this

NUCLEAR FISSION AND NUCLEAR POWER

Nuclear Fission - A reaction in which a heavy nucleus splits with another particle, with the release of energy.

Nuclear fission starts when neutrons are fired at the fuel causing some of its large, unstable nuclei to split into 2 smaller nuclei of roughly equal size

Each split nucleus also releases 2 or 3 more neutrons and lots of energy.

In nuclear reactors a chain reaction is set up.

1. Uranium atoms split releasing energy so fuel becomes hot.

2. This heats the water turning it into steam.

3. The steam turns the turbine

4. The turbine turns a generator and electricity is produced

5. The electricity goes to the transformers to produce the correct voltage.

LOW LEVEL WASTE

• Slightly radioactive
• Comes from things like paper//gloves
• Can be disposed by burying it in landfill sites

INTERMEDIATE LEVEL WASTE

• Things like the metal cases off the fuel rods, waste from hospitals etc
• Will stay for tens of thousands of years
• Sealed into concrete blocks the put into steel canisters for storage

HIGH LEVEL WASTE

• Comes from nuclear power stations and generates lots of heat
• Sealed in glass and steel for about 50 years before moved to permanent storage

It's difficult to find suitable places to bury//store waste because the site needs to be geologically stable so most intermediate/high level waste is stored in nuclear power stations