Teaching Resources

Episode 511: Absorption experiments

This gives students the opportunity to work with radioactive sources.

Summary

Student experiments: Absorption of radiation + 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

TAP 511-1: Use a spark counter. 

Range of beta radiation

TAP 511-2: The range of beta particles in aluminium and lead

Range of gamma radiation

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

TAP 511-3: Absorption in a liquid

Absorption of gs 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.)

TAP 511-4: Absorbing radiations

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.

TAP 511-5: Absorption in biological materials

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 as, bs and gs emitted. Challenge students to use absorbers to establish that all three radiation types are being emitted.  (The maximum energies are: a = 7.7 MeV, b = 3.3 MeV, g = 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.

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.

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