Radioactive decay and half-lifeEdexcel A-Level Physics: Flashcards
What these 13 flashcards ask
- What does it mean that radioactive decay is random?
- What does it mean that radioactive decay is spontaneous?
- Define activity.
- State the equation linking activity and the number of nuclei.
- What is the decay constant?
- Write the differential equation for radioactive decay.
- State the exponential decay equations.
- Define half-life.
- State the equation linking half-life and decay constant.
- What is the log form of the decay equation?
- What does a graph of ln A against t show?
- What fraction of a sample remains after n half-lives?
- Why are late readings less reliable when finding a half-life?
Exam questions on Radioactive decay and half-life
- A student counts the radiation from a long-lived radioactive source using a GM tube. She records the number of counts in each of ten successive 10-second intervals: 46, 53, 49, 55, 44, 51, 48, 52, 47 and 55. The activity of the source can be taken as constant throughout.Explain why the counts differ from one interval to the next, and state what the student should do to make the count rate more precise.2 marks
- A sample of an iodine isotope contains undecayed nuclei at a particular time. The half-life of the isotope is 8.0 days. Take 1 day = 86 400 s.Calculate the activity of the sample 24 days later.2 marks
- Technetium-99m is used as a radioactive tracer in hospitals. A sample of it has an activity of 400 MBq at 09:00, and its half-life is 6.0 hours. A scan needs the activity of the sample to have fallen to 60 MBq.Calculate the decay constant of technetium-99m in s⁻¹.3 marks
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).