LV Physics - Radioactivity

Atomic number

Number of protons

Mass number

Number of neutrons and protons combined

Radioactivity

The property possessed by some elements or isotopes of spontaneously emitting energetic particles by the disintegration of their (unstable) atomic nuclei

Alpha properties

Alpha particles are the nuclei of helium atoms and is formed from two protons and two neutrons. Alpha decay is a type of radioactive disintegration in which an alpha particle is emitted from a nucleus and it causes the nucleus to change into another nucleus with a smaller mass and atomic number than the original one: 92 238 U --> 90 234 Th + 2 4 He. Alpha radiation's ionisation powers are very strong but it can be stopped by paper.

Beta properties

Beta particles are electrons. When a neutron turns into a proton and an electron a beta particle is made and ejected. When the electron is ejected it does not change the mass however it carries away a negative charge so the atomic number of the element increases by 1: 6 14 C --> 7 14 N + -1 0 e. Beta radiation's ionising power is medium and can be stopped by aluminium.

Gamma properties

When some nuclei decay by emitting an alpha or beta particle they also emit a gamma ray which are electromagnetic waves like light. They carry away a lot of energy from the nucleus and leaves it in a more stable state. Gamma rays have no mass or charge so there is no change to the atomic or mass number when one is emitted. Gamma radiation has the weakest ionisation power but can only be stopped by thick lead.

What is the name of the photographic film that can detect ionising radiation?

Geiger-Muller

Sources of Background Radiation

Soil, ground, rocks containing radioactive isotopes

What does the activity of a radioactive source do over time?

Decreases

What is radioactivity measured in?

Becquerels (Bq)

Half-Life

The time taken for the number of unstable nuclei within a sample to halve

Uses of Alpha radiation in industry and medicine

It can provide heat for a spacecraft and is used in smoke detectors.

Uses of Beta radiation in industry and medicine

It is used for tracers and monitoring the thickness of materials.

Uses of Gamma radiation in industry and medicine

It is used in the treatment of cancer and sterilising medical instruments.

Contamination

Radioactive material has been introduced into or onto an object. Eg: Injecting an apple with radioactive material

Irridation

Object has been exposed to radiation. Eg: Shining gamma rays onto an apple

Dangers of Ionising Radiation

• Radiation can cause mutations in living organisms

• Radiation can damage cells and tissue

Nuclear Fission

Splitting of a large nucleus into smaller nuclei with the release of energy

Nuclear Fusion

Joining of light nuclei to form heavier nuclei with the release of energy

What are nuclear reactions a source of?

Energy

What does the fission of U-235 produce?

Two radioactive daughter nuclei and a small number of neutrons

Role of Control rods in the fission process

Absorb neutrons and slow the rate of the reaction

Role of the Moderator in the fission process

Slows down the neutrons

Slow neutrons are more easily absorbed

Role of shielding of a nuclear reactor

Prevents radiation from escaping so to not damage organisms

What is nuclear fusion the energy source for?

Stars

Why does nuclear fusion not happen at low temperatures and pressures?

For fusion to occur, the particles must overcome the strong electrostatic forces of repulsion which requires very high temperatures and pressures.