Radioactive decay and half-lifeEdexcel A-Level Physics: Mind map

Exam questions on Radioactive decay and half-life

1. 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
2. A sample of an iodine isotope contains $2.4 \times 10^{15}$ 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
3. 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