Ionising Radiation
Quantum and Nuclear

Episode 511: Absorption experiments

Lesson for 16-19 IOP TAP

This gives students the opportunity to work with radioactive sources.

Lesson Summary

  • Student experiments: Absorption of radiation and report back (40 minutes)
  • Demonstration: Absorption of radiation by living matter
  • Student experiment (optional)

Student experiments

Groups could work in parallel and report back to a plenary session.

Remind them to correct for the background count (taken at least twice – at the start and end of the main experiments and the two results averaged).

Range of alpha radiation

Episode 511-1: Use a spark counter (Word, 62 KB)

Range of beta radiation

Episode 511-2: The range of beta particles in aluminium and lead (Word, 38 KB)

Range of gamma radiation

An optical analogue for the absorption of γ particles by lead is the absorption of light by successive microscope slides.

Episode 511-3: Absorption in a liquid (Word, 54 KB)

Absorption of γ particles is an example of exponential decrease – check the data for a constant half thickness, thus suggesting the type of physics involved. (Each mm of absorber is reducing the intensity by the same fraction.)

Episode 511-4: Absorbing radiations (Word, 38 KB)

Demonstration: Absorption of radiation by living matter

To simulate the absorption of radiation by living matter use slices of different vegetables as absorbers, or a slice of bacon to represent human flesh.

Episode 511-5: Absorption in biological materials (Word, 53 KB)

Student experiments: Optional

The first requires a sealed radium-226 source. Because Ra-226 is the parent to a chain of radioactive daughters, granddaughters and so on, you get a mixture of αs, βs and γs emitted. Challenge students to use absorbers to establish that all three radiation types are being emitted. (The maximum energies are: E α  = 7.7 MeV E β  = 3.3 MeV E γ  = 2.4 MeV)

The second is an extension of the β absorption experiment. You could speculate that some β particles might be back-scattered (like Rutherford’s α particle scattering that first demonstrated the existence of the nucleus). A quick try shows that some β particles are indeed back-scattered.

Radioactive sources

Follow the local rules for using radioactive sources, in particular do not handle radioactive sources without a tool or place them in close proximity to your body. Deliberately placing a radioactive source in contact with the skin would increase your dose of ionising radiation unnecessarily and increase the risks to your health. This is a criminal offence.

Ionising Radiation
is used in analyses relating to Radioactive dating
can be analysed using the quantity Half-Life Decay Constant Activity
features in Medical Physics
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