GCSE AQA Physics - Atomic Structure

(history of the atom covered in chemistry)

Alpha radiation

When an alpha particle is emitted from the nucleus

Alpha particle

Two neutrons and two protons (helium nucleus)

Alpha particle penetration and ionising power

• Travel a few cm in air, and are absorbed by paper

• Strongly ionsing

Beta particle

Fast- moving electron

What happens for every beta particle emitted from the nucleus?

A neutron in the nucleus turns into a proton.

beta particle penetration and ionising power

• few metres in air, absorbed by a sheet of aluminium

• moderately ionising

Gamma rays

Waves of electromagnetic radiation released by the nucleus.

Gamma ray penetration and ionsing

• Penetrate far into materials (lead or concrete) and have a long distance through air

• Weakly ionsing

How do unstable isotopes become more stable?

By decaying into other elements and giving out radiation.

Ionising radiation

Radiation that can knock electrons off an atom.

Count-rate

The number of radiation counts reaching the Geiger-Muller tube per second.

Describe the nature of radioactive decay

It is entirely random and unpredictable.

Activity

The rate at which a source decays

What is activity measured in?

becquerels, Bq

Half-life

The time taken for the number of nuclei of a radioactive source to halve.

What will happen to the activity each time a radioactive source decays?

It will decrease.

Background radiation

Low-level radiation that is around us all the time.

Give 3 examples of background radiation

• Radioactivity of naturally occurring unstable isotopes (radon gas in rocks)

• Radiation from space (cosmic rays)

• Radiation due to human activity (fallout, nuclear waste)

Irradiation

Exposure to radiation.

Contamination

When a radioactive source gets onto or into an object.

How can we protect against irradiation and contamination?

• Maintaining distance from the radioactive source

• Limiting time near the source

• Shielding from the radiation using gloves, tongs and protective suits

Why are beta and gamma radiation the most dangerous outside the body?

Because they can penetrate the body and get to delicate organs.

Why are alpha sources most dangerous inside the body?

Because they do all of their damage in a very localised area.

Why should studies on radiation be peer-reviewed?

Because they are important for human health

Why is radiation dangerous?

It can lead to tissue damage, by entering living cells and ionising atoms and molecules.

How are radioactive sources used as medical tracers?

They are injected into the body and their progress around the body can be detected using an external detector.

Why are isotopes used as medical tracers need a short half-life?

So the radioactivity inside the patient quickly decreases.

Why is gamma radiation used for medical tracers?

So the radiation passes out of the body without causing much ionisation.

Describe radiotherapy

Gamma rays are carefully directed at the right dosage to kill cancer cells without causing much harmer to normal cells.

Describe how radio-emitting implants are used

They are placed next to or inside tumours to kill them.

How may the positives of radiotherapy outweigh the negatives?

Whilst the exposure to radiation poses future risks and side effects, it can get rid of the cancer entirely.

Nuclear fission

A nuclear reaction which releases energy from large unstable nuclei by splitting them into smaller nuclei.

Spontaneous fission

Fission that occurs without any external trigger.

Induced fission

Fission that occurs when the nucleus absorbs a neutron

What are the products of nuclear fission?

• 2 new lighter elements

• 2 or 3 neutrons

• Energy

What do all of the products of fission have?

Kinetic energy

How can a chain reaction occur?

If a neutron released when an atom splits goes onto be absorbed by another nucleus, this can cause more fission to occur.

How is the energy from fission used to generate electricity?

It heats water, making steam to turn a turbine which turns a generator.

How can we control fission in a nuclear reactor?

By lowering control rods inside the reactor, which absorb neutrons and control the chain reaction.

Nuclear fusion

A nuclear reaction in which two light nuclei join to form a heavier nucleus, releasing a large amount of energy.

What happens to some of the mass of the lighter nucleus in fusion?

It is converted into energy and released.