Resources: Class presentation and handout.
Handout: Make notes on the history of half-life experiments and links to alpha scattering experiment. Practice applying half-life definitions to maths-based questions involving fractions. Apply knowledge of half-life to deduce how information can be used to explore the best isotopes to use with living organisms.
Radioactive materials decay naturally and release alpha, beta or gamma radiation. What is the name given to the number of nuclei that decay each second? Use some examples of proportion in ratio to introduce the concept of half-life.
Use the handout to reinforce learning. Stress the connections between the scientific community of that time: Geiger and Marsden were assistants to Rutherford for the alpha scattering experiment. Discuss how that lead to the electrometer and then the Geiger-Muller Counter. Practice the calculations of half-life, time and sample remaining. Ask the students to collectively solve the problems and explain their calculations. Use all of the problems that provide data on this lesson’s handout to plot different graphs to practice plotting the data. Use graph data to make a comparison between the radioactivity of different isotopes. In the example, which isotope has the shortest half-life? Discuss the applications of different isotopes for medical treatments – in the example here, why is iodine 131 a better treatment for thyroid cancer?
Career Film: This is Billy Keywood. Billy works as a Graduate Scientist for National Nuclear Laboratory.
Expert Film: This is Billy Keywood. Billy works as a Graduate Scientist for National Nuclear Laboratory. and explains about the half-life of a radioactive isotope.
Use the handout to link the historical context to the alpha scattering experiment. Apply the definition of half-life to calculator based questions. Given half-lives, students can work out how much of a sample will be left. Given a count rate, they can deduce the half-life. Use the information on half-life to predict the safety and use of isotopes for living organisms.
Challenge Task: Complete the more challenging questions on the second handout sheet. Present students with information about Strontium 90. “Strontium 90 can be absorbed by bones if ingested. It has a half-life of 28years, it is a beta emitter.” Why is it such a health hazard? How long would it take for the activity level to fall to 5% or its original value?
Complete the summative quiz on the presentation to assess learning. Discuss the isotope technetium 99m. Explain that is a gamma emitter. Discuss the benefits of using a gamma emitter. Discuss what other factors would need to be considered when using a radioactive tracer in the body.