Uses of Radiation — AQA GCSE Combined Science Trilogy 8464 - Physics Revision Notes & Topical Questions

Section 1 of 9Choosing a source (Extended)

Choosing a source (Extended)

Type of radiation and half-life

• Type of radiation and half-life together they decide which isotope suits a job.

Alpha

• Alpha must be in the open since almost anything stops it.

Gamma

• Gamma suits uses where the radiation must pass through material.

Short half-life

• Short half-life preferred for tracers and medical uses so the activity does not stay in the patient.

Long half-life

• Long half-life chosen for sources that must stay reliable for years.

Section 2 of 9Smoke detectors

1

A source of americium-241 emits alpha particles into a small chamber.

2

The alpha particles ionise the air, so a small steady current flows between two electrodes.

3

Smoke absorbs the alpha particles, so the current falls.

4

A microchip detects the fall and triggers the alarm.

Why alpha

• Why alpha it ionises air strongly but is stopped by the casing, so it is harmless outside.

Why beta or gamma not

• Why beta or gamma not they would pass straight through the smoke and the alarm would not sound.

Half-life

• Half-life a long half-life means the detector works for many years.
  • (about 430 years)

Section 3 of 9Thickness control

Setup

• Setup a material moves across a radiation source and a detector on the other side monitors the particles that pass through.

Thicker material

• Thicker material more particles are absorbed, so the count falls.

Thinner material

• Thinner material the count rises and the machine adjusts to keep the thickness constant.

Beta

• Beta used for thin materials such as paper, plastic film and aluminium foil because it is partially absorbed.

Gamma

• Gamma used for very thick materials.

Half-life

• Half-life many years (10–20 years) so the count rate stays steady.

Section 4 of 9Sterilisation and food irradiation

Sterilising equipment

• Sterilising equipment gamma rays sterilise medical equipment,
  • and the most penetrating radiation reaches all sides through the packaging without making it radioactive.

Irradiating food

• Irradiating food gamma radiation kills bacteria, so the food lasts longer and the risk of food-borne infection falls.

Radura

• Radura the symbol carried by irradiated food.

Half-life

• Half-life the gamma source has a half-life of about 5 years.
  • (such as cobalt-60)

Section 5 of 9Diagnosis and treatment of cancer

Radiotherapy

• Radiotherapy beams of gamma rays are directed at a tumour from several directions to kill cancer cells while minimising harm to healthy tissue.

Gamma

• Gamma it penetrates the body to reach the tumour, and the source has a half-life of about 5 years.

Tracer

• Tracer a radioactive isotope that tracks the movement of substances such as blood around the body.

PET scan

• PET scan it detects emissions from a tracer to diagnose cancer and locate a tumour.

Tracer half-life

• Tracer half-life several hours, long enough for a scan and short enough that the radiation soon leaves the body.

Section 6 of 9Other uses

Leak detection

• Leak detection a gamma tracer in the fluid of an underground pipe collects at leaks, which a detector at the surface finds.

Radioactive dating

• Radioactive dating the proportion of carbon-14 in once-living remains falls with a half-life of about 5700 years, giving the age of the sample.

Power

• Power heat from fission in reactors, or from the decay of plutonium-238 in space probes, can be converted to electricity.

Weld inspection

• Weld inspection gamma sources and photographic film reveal cracks in pipes and aircraft parts.

Section 7 of 9More from the specification

More from the specification

Radiation sorting in magnetic fields

• Radiation sorting in magnetic fields passing mixed emissions through transverse magnetic fields separates alpha and beta particles by opposite trajectory curvature.

Atomic Nuclear Structure

• The atomic nucleus contains nucleons, surrounded by orbital electrons with equal negative charge.
  • (positively charged protons and neutral neutrons)

Radioactive Isotopes in Industrial Thickness Gauges

• Beta radiation emitted from unstable radioisotopes passes through manufactured paper or metal sheets,
• regulating thickness by monitoring count rates.

Medical Tracers and Nuclear Diagnosis

• Gamma-emitting isotopes with short half-lives are introduced into the body, emitting penetrating radiation detectable outside while minimizing tissue damage.
  • (e.g. technetium-99m)

Correcting for Background Count Rates

• Natural background radiation from environmental rock formations and cosmic rays must be subtracted from measured activity to evaluate true sample emissions.

Decay equation

• An equation in nuclide notation with balanced nucleon and proton numbers.

Kinetic energy

• K = ½mv², energy of motion.

Nucleus

• Small, dense, positively charged centre of the atom.

Neutron

• Neutral particle in the nucleus, relative mass 1.

Proton

• Positive particle in the nucleus, relative charge +1 and relative mass 1.

Charge

• Quantity of electricity in coulombs, Q = It.
  What the symbols mean: Q = charge (C) · I = current (A) · t = time (s)

Background radiation

• Radiation that is always present in the environment.

Unstable nucleus

• A nucleus with an imbalance of protons and neutrons that may decay.

Electric field

• Region of space in which a charge experiences a force.

Magnetic field

• Area around a magnet where its effects can be detected.

Section 8 of 9Key terms

Term	Meaning
Tracer	Radioactive isotope used to follow substances around the body or a pipe.
Radiotherapy	Treating cancer with radiation.
Smoke detector	Alarm using alpha particles that ionise air.
Half-life	Time for half the nuclei in a sample to decay.
Radura	Symbol on irradiated food.

Section 9 of 9Exam technique

1

Choosing an alpha source for thickness testing — alpha would not pass through the material.

2

Saying a tracer should have a long half-life — it should be short.

3

Thinking sterilising with gamma makes the object radioactive — it does not.

4

Saying carbon dating works for objects that were never alive.