Episode 511: Absorption experiments

This gives students the opportunity to work with radioactive sources.

Geiger tube set up to measure absorption

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

Absorption of light by glass slides

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

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

Absorption of γs 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: α = 7.7 MeV, β = 3.3 MeV, γ = 2.4 MeV).

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

Radiation hazard symbol

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.

Download this episode
Episode 511: Absorption experiments (Word, 215 KB)