Radioactive decay and half-lifeEdexcel International A Level Physics: Flashcards

What these 13 flashcards ask

What does it mean to say that nuclear decay is spontaneous?
What does it mean to say that nuclear decay is random?
What is activity and what is its unit?
State the equation linking activity and the number of nuclei.
What is the decay constant?
State the differential equation for radioactive decay.
Give the equations for N and A as functions of time.
Define half-life.
What is the relationship between λ and half-life?
State the log form of the decay equation.
What does a graph of ln A against t look like?
How can you find the half-life from an activity-time graph?
Why do count readings from a steady source vary?

Exam questions on Radioactive decay and half-life

A student sets up a Geiger–Müller tube and counter close to a long-lived source, whose half-life is many years, so its activity is effectively constant during the experiment. She records the number of counts in each of five successive 10 s intervals: 52, 47, 58, 44 and 55.
Explain why the counts in the five intervals are different even though the activity of the source is constant.2 marks
Iodine-131 is a radioactive isotope with a half-life of 8.0 days. A hospital stores a sample of iodine-131 whose activity is 640 kBq. Use 1 day = 86 400 s.
Calculate the number of undecayed iodine-131 nuclei in the sample when its activity is 640 kBq.2 marks
A student measures the corrected activity of a sample of a radioactive isotope at regular intervals and obtains the following values: 480 Bq at 0 s, 340 Bq at 40 s, 240 Bq at 80 s, 170 Bq at 120 s and 120 Bq at 160 s.
Determine the half-life of the isotope from these results.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).