Use of Radioactive Isotopes (SQA National 5 Chemistry): Revision Note

Using isotopes

• Radioisotopes have a wide range of uses in medicine and industry

• You need to be able to look at information about an isotope and evaluate its suitability for a particular job

• To do this, two key properties should be considered:

  • The type of radiation emitted

  • The half-life of the isotope

Choosing the right type of radiation

• The choice of alpha, beta, or gamma depends on the job

• The main consideration is penetrating power

Alpha (α)

• Alpha radiation has low penetrating power

• It is stopped by paper

  • It cannot pass through skin

• It is only useful if the source is very close to the target and in the open air

  • A good example of using alpha radiation is inside a smoke detector

Beta (β)

• Beta radiation has medium penetrating power

• It is stopped by aluminium

  • It can penetrate skin but not dense bone

• It is useful for monitoring the thickness of materials like paper or aluminium foil

Gamma (γ)

• Gamma radiation has the highest penetrating power

• It is stopped by thick lead or concrete

• It is used for tasks that require the radiation to pass through objects or the human body, such as:

  • Sterilising equipment

  • Treating internal tumours

Choosing the right half-life

• The choice of half-life depends on how long you need the source to be active

Long half-life (years)

• This is needed for jobs where the source must work reliably for a long time without being replaced

• Examples include smoke detectors and industrial thickness gauges

Short half-life (hours or days)

• This is essential for medical tracers that are put inside the human body

• This is because the isotope needs to:

  • Last long enough for the scan to be completed

  • But, decay quickly afterwards to minimise the radiation dose to the patient