(7.4-7.9) Alpha, beta particles and gamma rays

What is radiation?

Energy transfer via electromagnetic waves

Why does radiation occur?

Due to imbalances in the forces within the nucleus, being too big or having too many or too few neutrons, some nuclei are unstable.

They can emit radiation to become more stable, in the form of a high energy particle or wave.

The radiation taken some energy with it as it moves away, reducing the energy of the nucleus and making it more stab;e.

This is called radioactive decay, a random process that cannot be predicted.

How does nuclear radiation occur?

When an unstable nuclei decays, the radiation it emits is called nuclear radiation.

What are the three types of nuclear ionising radiation?

Alpha (α)

Beta (β^-)

Gamma (γ)

Describe alpha particles in terms of:

• atomic make up (particle/ray, creation, structure, charge)

• range

• penetration

• ionisation

• effects on atomic number

• effects on mass number

• equation + explanation

• Alpha particle = helium nucleus (2 neutrons + 2 protons)

• charge of +2 - can be affected by electric field

• Range of a few cm

• Penetration stopped by paper

• High ionising power

When the alpha particle is emitted, mass no. decreases by 4, atomic no. decreases by 2. Charge also decreases by 2.

Describe beta particles in terms of:

• atomic make up (particle/ray, creation, structure, charge)

• range

• penetration

• ionisation

• effects on atomic number

• effects on mass number

• equation + explanation

• Beta particles are fast moving particles which are produced when a neutron becomes a proton and an electron

• The electron is emitted, proton stays in the nuclei

• Charge of -1, can be affected by electric field

• Penetration stopped by aluminium

• Medium ionisation

• mass number stays the same

• atomic number increases by one - proton

Describe gamma rays in terms of:

• atomic make up (particle/ray, creation, structure, charge)

• range

• penetration

• ionisation

• effects on atomic number

• effects on mass number

• equation + explanation

• A ray is emitted from an unstable nucleus

• the nucleus becomes less energetic but does not change its structure

• An infinite range

• Penetration reduced by lead

• Low ionisation

• the mass and atomic number remain the same

Describe neutron emission in terms of:

• atomic make up (particle/ray, creation, structure, charge)

• effects on atomic number

• effects on mass number

• Small number of isotopes can decay through neutrons

• The proton number does not change.

• The nucleon number decreases by 1.

Detail the experiment to investigate the penetration powers of different types of radiation.

1. Measure background radiation with a Geiger-Muller counter for 1 minute. Repeat 3 times and average.

2. Place a radioactive source a fixed 3 cm from the tube and take readings of 1 minute.

3. Now take absorbers: paper, thicknesses of aluminium and thicknesses of lead.

4. One at a time, place these between the source and the tube and take another reading over a 1 minute period.

5. Repeat the experiment for other radioactive sources and measure against background noise and difference in counter.

What is a Geiger-Muller counter?

An electronic instrument used to measure ionising radiation through detecting ionised atoms. Counted in Becquerels.

How does photographic film detect radiation?

It becomes barker when it absorbs radiation and is used to monitor radiation exposure.