Detailed Notes: 8. Nuclear Physics: Paper 2: Physics A Level AQA

Rutherford scattering

Rutherford scattering demonstrated the existence of a nucleus.

Most alpha particles passed straight through the foil with no deflection

This suggested that the atom is mostly empty space (and not a uniform density as suggested by the plum pudding model).

A small amount of particles were deflected by a large angle.

This suggested that the centre of the atom is positively charged, as positively charged alpha particles were repelled from the centre and deflected.

Very few particles were deflected back by more than 90°.

This suggested that the that the centre of the atom was very dense as it could deflect fast moving alpha particles, but also that is was very small as a very small amount of particles were deflected by this amount.

Radiation

Radiation is where an unstable nucleus emits energy in the form of EM waves or subatomic particles in order to become more stable.

Three types of radiation.

1. Alpha (α)

2. Beta (β)

3. Gamma (γ)

Sources of background radiation.

1. Radon gas

2. Artificial sources

3. Cosmic rays

4. Rocks

Radon gas

Released from rocks.

Artificial sources

caused by nuclear weapons testing and nuclear meltdowns.

Cosmic rays

Enter the Earth’s atmosphere from space.

Rocks

Containing naturally occurring radioactive isotopes.

Radioactive decay

Radioactive decay is a random process meaning you can’t predict when the next decay will occur.

Decay constant

The decay constant can be used to model the decay of a nuclei only when there is a large number of nuclei in a sample, this is because the decay constant models the number of nuclei decayed by statistical means.

Critical mass

The critical mass is the minimum mass of fuel required to maintain a steady chain reaction.

Moderator

This slows down the neutrons released in fission reactions to thermal speeds through elastic collisions between the nuclei of the moderator atoms and the fission neutrons.

Control rods

Absorb neutrons in the reactor in order to control chain reactions.

Coolant

Absorbs the heat released during fission reactions in the core of the reactor.