Episode 511: Absorption experiments
Lesson
for 16-19
- Activity time 40 minutes
- Level Advanced
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.
